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  • 1.
    Abdi, Amir
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Ignatowicz, Monika
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Gunasekara, Saman Nimali
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Chiu, Justin NingWei
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Martin, Viktoria
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Experimental investigation of thermo-physical properties of n-octadecane and n-eicosane2020In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 161, article id 120285Article in journal (Refereed)
    Abstract [en]

    Reliable knowledge of phase change materials (PCM) thermo-physical properties is essential to model and design latent thermal energy storage (LTES) systems. This study aims to conduct a methodological measurement of thermo-physical properties, including latent enthalpy, isobaric specific heat, thermal conductivity and dynamic viscosity, of two n-alkanes, n-octadecane and n-eicosane. The enthalpy and isobaric specific heat of the materials are measured via differential scanning calorimetry (DSC) technique, using a pDSC evo7 from Setaram Instrumentation with a sample mass of 628.4 mg. The influence of the scanning rates, varying from 0.5 K/min to 0.025 K/min, in dynamic continuous mode within temperature range of 10-65 degrees C is investigated. The thermal conductivity and the dynamic viscosity are measured via Hot Disk TPS-2500S instrument and Brookfield rotational viscometer, respectively, up to 70 degrees C. The thermal analysis results via the pDSC show that the isothermal condition can be approached at a very low scanning rate, however at the cost of a higher noise level. A trade-off is observed for n-octadecane, achieving the lowest deviation of 0.7% in latent heat measurement at 0.05 K/min, as compared to the American Petroleum Table values. For n-eicosane, the lowest deviation of 1.2% is seen at the lowest scanning rate of 0.025 K/min. The thermal conductivity measured values show good agreements with a number of documented literature studies in the solid phase, within deviations of 2%. Larger deviations of 5-16% are found for the measurement in the liquid phase. The viscosity values also show a good agreement with the literature values with maximum deviations of 2.9% and 6.3%, with respect to the values of American Petroleum Tables, for n-octadecane and n-eicosane, respectively. The good agreements achieved in measurements establish the reliable thermo-physical properties contributing to the future simulations and designs. 

  • 2.
    Albernaz, Daniel L.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Do-Quang, Minh
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Simulation of a suspended droplet under evaporation with Marangoni effects2016In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 91, p. 853-860Article in journal (Refereed)
    Abstract [en]

    We investigate the Marangoni effects in a hexane droplet under evaporation and close to its critical point. A lattice Boltzmann model is used to perform 3D numerical simulations. In a first case, the droplet is placed in its own vapor and a temperature gradient is imposed. The droplet locomotion through the domain is observed, where the temperature differences across the surface is proportional to the droplet velocity and the Marangoni effect is confirmed. The droplet is then set under a forced convection condition. The results show that the Marangoni stresses play a major role in maintaining the internal circulation when the superheated vapor temperature is increased. Surprisingly, surface tension variations along the interface due to temperature change may affect heat transfer and internal circulation even for low Weber number. Other results and considerations regarding the droplet surface are also discussed.

  • 3.
    Ali, Rashid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Dryout Characteristics During Flow Boiling of R134a in Vertical Circular Minichannels2011In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 54, no 11-12, p. 2434-2445Article in journal (Refereed)
    Abstract [en]

    In this paper, the experimental results of dryout during flow boiling in minichannels are reported and analysed. Experiments were carried out in vertical circular minichannels with internal diameters of 1.22 mm and 1.70 mm and a fixed heated length of 220 mm. R134a was used as working fluid. Mass flux was varied from 50 kg/m(2) s to 600 kg/m(2) s and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 degrees C and 32 degrees C. Experimental results show that the dryout heat flux increases with mass flux and decreases with tube diameter while system pressure has no clear effect for the range of experimental conditions covered. Finally, the prediction capabilities of the well known critical heat flux (CHF) correlations are also tested.

  • 4.
    Anghel, Ionut Gheorghe
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Post-dryout heat transfer to high-pressure water flowing upward in vertical channels with various flow obstacles2012In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 55, no 25-26, p. 8020-8031Article in journal (Refereed)
    Abstract [en]

    Post-dryout heat transfer to high pressure water was investigated experimentally in vertical tubes and annuli containing various flow obstacles. The operational conditions during the experiments were as follows: mass flux from 500 to 1750 kg/m(2) s. pressure from 5 to 9 MPa, inlet subcooling from 10 to 40K and heat flux up to 1.5 MW/m(2). Five different test sections were used in experiments: three annular test sections with inner diameter 12.7 mm and outer diameter 24.3 mm, containing cylindrical and grid flow obstacles in the upper part, and two tubular test sections with inner diameter 24.3 mm with and without pin flow obstacles. The heated length in all test sections was 3650 mm. The wall temperature was measured with 88 thermocouples located along the inner rod and the outer tube surfaces. Due to the presence of flow obstacles, only developing post-dryout heat transfer was observed. Selected post-dryout heat transfer correlations were compared to the experimental data. It has been concluded that all tested correlations predict significantly higher wall temperatures than those obtained in the present experiment. A simple correction function to the Saha model has been suggested which significantly improves the agreement between the correlation and the present data.

  • 5.
    Attarzadeh, Reza
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Rovira, Marc
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Duwig, Christophe
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Process Technology.
    Design analysis of the "Schwartz D" based heat exchanger: A numerical study2021In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 177, article id 121415Article in journal (Refereed)
    Abstract [en]

    Triply Periodic Minimal Surfaces (TPMS) have promising thermophysical properties, which makes them a suitable candidate in the production of low-temperature waste heat recovery systems. A TPMS thermal performance is connected to the complex flow patterns inside the pores and their interactions with the walls. Unfortunately, the experimental study's design analysis and optimization of TPMS heat exchangers are complicated due to the flow pattern complexity and visual limitations inside the TPMS. In this study, three-dimensional steady-state, conjugate heat transfer (CHT) simulations for laminar incompressible flow were carried out to quantify the performance of a TPMS based heat exchanger. TPMS Lattices based on Schwartz D architecture was modeled to elucidate the design parameters and establishing relationships between gas velocity, heat transfer, and thermal performance of TPMS at different wall thicknesses. In this study, four types of lattices from the same architectures with varying wall thickness were examined for a range of the gas velocity, with one design found to be the optimized lattice providing the highest thermal performance. The results and methodology presented here can facilitate improvements in TPMSheat exchangers' fabrication for recycling the waste heat in low pitch thermal systems.

  • 6.
    Bandaru, S V Ravikumar
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Villanueva, Walter
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Konovalenko, Alexander
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Komlev, Andrei A.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Thakre, Sachin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Sköld, Per
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Bechta, Sevostian
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Upward-facing multi-nozzle spray cooling experiments for external cooling of reactor pressure vessels2020In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 163, article id 120516Article in journal (Refereed)
    Abstract [en]

    Cooling by water spray is a well-known technology that can reach significantly higher Critical Heat Flux (CHF) compared to other cooling methods. For the light water reactor safety, the in-vessel retention (IVR) by external reactor vessel cooling (ERVC) is a comprehensive severe accident management strategy to arrest and confine the corium in the lower head of the reactor pressure vessel. Heat fluxes up to 1.5 MW/m2 have already been assumed attainable in low-power nuclear reactors while cooling required in high-power reactors is expected to reach 2.5 MW/m2. Instead of reactor lower head flooding and relying on cooling due to natural convection, a viable and more efficient alternative is to spray the external surface of the vessel. Given all the advantages of spray cooling reported in the literature, a lab-scale experimental facility was built to validate the efficiency of multi-nozzle spray cooling of a downward-facing heated surface inclined at different angles up to 90o. The facility employed a 2×3 matrix of spray nozzles to cool the FeCrAl alloy foil with an effectively heated surface area of 96 cm2 using water as the coolant. Heat loads and surface inclinations were varied parameters in the test matrix. The results show that no significant variations in spray cooling performance concerning the inclination of the heated surface. A surface heat flux of 2.5 MW/m2 was achieved at every inclination of the downward-facing surface. The results also indicate that more uniform liquid film distribution could be obtained for some inclinations, which in turn leads to maintaining low surface temperature. The obtained surface heat flux margin by spray cooling indicates that it is feasible to adopt IVR-ERVC strategy for a large power reactor.

  • 7. Belyakov, Nikolay
    et al.
    Nosko, Oleksii
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Analytical solution of non-stationary heat conduction problem for two sliding layers with time-dependent friction conditions2016In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 98, p. 624-630Article in journal (Refereed)
    Abstract [en]

    In this article we conduct an overview of various types of thermal contact conditions at the sliding interface. We formulate a problem of non-stationary heat conduction in two sliding layers with generalized thermal contact conditions allowing for dependence of the heat-generation coefficient and contact heat transfer coefficient on time. We then derive an analytical solution of the problem by constructing a special coordinate integral transform. In contrast to the commonly used transforms, e.g. Laplace or Fourier transforms, the one proposed is applicable to a product of two functions dependent on time. The solution is validated by a series of test problems with parameters corresponding to those of real tribosystems. Analysis shows an essential influence of both time-dependent heat-generation coefficient and contact heat transfer coefficient on the partition of the friction heat between the layers. The solution can be used for simulating temperature fields in sliding components with account of this influence.

  • 8.
    Bergagio, Mattia
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Li, Haipeng
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering. Warsaw University of Technology, Poland.
    An iterative finite-element algorithm for solving two-dimensional nonlinear inverse heat conduction problems2018In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 126, p. 281-292Article in journal (Refereed)
    Abstract [en]

    It is often useful to determine temperature and heat flux in multidimensional solid domains of arbitrary shape with inaccessible boundaries. In this study, an effective algorithm for solving boundary inverse heat conduction problems (IHCPs) is implemented: transient temperatures on inaccessible boundaries are estimated from redundant simulated measurements on accessible boundaries. A nonlinear heat equation is considered, where some of the material properties are dependent on temperature. The IHCP is reformulated as an optimization problem. The resulting functional is iteratively minimized using a conjugate gradient method together with an adjoint (dual) problem approach. The associated partial differential equations are solved using the finite-element package FEniCS. Tikhonov regularization is introduced to mitigate the ill-posedness of the IHCP. The accuracy of the implemented algorithm is assessed by comparing the solutions to the IHCP with the correct temperature values, on the inaccessible boundaries. The robustness of our method is tested by adding Gaussian noise to the initial conditions and redundant boundary data in the inverse problem formulation. A mesh independence study is performed.

  • 9.
    Bergagio, Mattia
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Thiele, Roman
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Analysis of temperature fluctuations caused by mixing of non-isothermal water streams at elevated pressure2017In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 104, p. 979-992Article in journal (Refereed)
    Abstract [en]

    Temperatures were measured at the inner surface of an annulus between two coaxial tubes, where three water streams mixed. These temperatures were sampled at either 100 Hz or 1000 Hz. The acquisition time was set to 120 s. Two water streams at 549 K, with a Reynolds number between 3.56 × 105 and 7.11 × 105, descended in the annular gap and mixed with a water stream at 333 K or 423 K, with a Reynolds number ranging from 1.27 × 104 to 3.23 × 104. Water pressure was kept at 7.2 MPa. Inner-surface temperatures were collected at eight azimuthal and five axial positions, for each combination of boundary conditions. To better analyze these temperatures and mixing in the vicinity of the wall, scalars estimating the mixing intensity at each measurement position were computed from detrended temperature time series. Fourier and Hilbert–Huang marginal spectra were calculated for the time series giving rise to the highest values of a mixing estimator of choice. The relationship between temperature and velocity was explored by examining the results of an LES simulation using the same boundary conditions as in one of the experimental cases.

  • 10.
    Bian, Boshen
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Dovizio, Daniele
    bNuclear Research and Consultancy Group, the Kingdom of the Netherlands.
    Villanueva, Walter
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety. Nuclear Futures Institute, Bangor University, United Kingdom.
    Direct numerical simulation of internally heated natural convection in a hemispherical geometry2024In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 220, article id 124997Article in journal (Refereed)
    Abstract [en]

    Internally heated (IH) natural convection can be found in nature, industrial processes, or during a severe accident in a light water reactor. In this accident scenario, the nuclear reactor core and some internal structures can melt down and relocate to the lower head of the reactor pressure vessel (RPV) and interact with the remaining coolant. Subsequent re-heating and re-melting under decay and oxidation heat creates a transition from a debris bed to a molten pool. The molten pool, which can involve more than hundred tons of dangerously superheated oxidic and metallic liquids, imposes thermo-mechanical loads on the vessel wall that can lead to a thermal and/or structural failure of the vessel and subsequent release of radioactive materials to the reactor pit, and can possibly make its way to the environment. This study uses Direct Numerical Simulation (DNS) to investigate homogeneous IH molten pool convection in a hemispherical domain using Nek5000, an open-source spectral element code. With a Rayleigh number of 1.6 × 1011, the highest reached through DNS in this confined hemispherical geometry, and a Prandtl number of 0.5, which corresponds to a prototypic corium, the study provides detailed information on the thermo-fluid behavior. The results show a turbulent flow with three distinct regions, consistent with the general flow observations from the BALI experiments. The study also presents detailed information on turbulence, such as turbulent kinetic energy (TKE), turbulent heat flux (THF), and temperature variance. Additionally, the study provides 3D heat flux distributions along the boundaries. The heat fluxes along the top boundary fluctuate due to the turbulent eddies in the vicinity, while along the curved boundary the heat fluxes increase nonlinearly from the bottom to the top.

  • 11.
    Brethouwer, Gert
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Strong dissimilarity between heat and momentum transfer in rotating Couette flows2023In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 205, article id 123920Article in journal (Refereed)
    Abstract [en]

    Rotation influences flows and transport processes in many engineering applications, however, even in canonical flow cases, the effects of rotation are not fully understood. Here, we present the results of di-rect numerical simulations of heat transfer plane Couette and Taylor-Couette flows subject to rotation about the spanwise and axial axis, respectively. Temperature is a passive scalar since buoyancy is ne-glected. The Reynolds number Re and the rotation rate Rn are systematically varied to thoroughly inves-tigate the influence of rotation on heat and momentum transfer and the Reynolds analogy. We find that with increasing anti-cyclonic rotation, the Nusselt numbers for the momentum transfer Num and heat transfer Nuh both increase at first before declining and approaching unity at rapid rotation rates when the flow becomes fully laminar. The Reynolds analogy factor RA = N uh/N um is near unity for non-rotating Couette flows, but it grows significantly with increasing rotation rate. RA reaches a maximum of approx-imately 2 at low Re up to 6 and 8 near Rn = 1 at higher Re in plane Couette and Taylor-Couette flow, respectively. The simulations thus show that the Reynolds analogy between heat and momentum trans-fer breaks down and that the heat transfer can become much faster than moment transfer when plane Couette and Taylor-Couette flows are subject to anti-cyclonic rotation. This happens at low Re as well as higher Re when the flows are fully turbulent. The turbulent Prandtl becomes much smaller than unity and the mean velocity and temperature profiles differ when the Reynolds analogy breaks down. We also present empirical models for Num and RA , which agree reasonably well to very well with the data within a limited Rn range.

  • 12.
    Deng, Yucheng
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Guo, Qiang
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Xiang, Yan
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Fang, Heng
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Robotics, Perception and Learning, RPL.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    An experimental study on the effect of chemical additives in coolant on steam explosion2024In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 218, article id 124818Article in journal (Refereed)
    Abstract [en]

    In assessment of severe accident risk in light water reactors (LWRs), steam explosion is a nonnegligible phenomenon following a relocation of core melt (corium) into coolant, and thus various research efforts have been paid to steam explosion. There had been numerous studies showing that the occurrence of steam explosions is influenced by several factors such as melt and coolant temperatures, melt materials, non-condensable gasses, etc. However, most of the existing experiments used deionized (DI) water or tap water as coolant, with little consideration of the effect of chemicals (e.g. boric acid, sodium hydroxide, sodium phosphate) commonly applied in reactor coolant. To examine the effect of the chemical additives in coolant on steam explosion, the present study performs a series of molten Tin droplet-coolant interaction tests using DI water and different chemical solutions, including H3BO3 solutions, NaOH + H3BO3 neutral solutions, and Na3PO4 + H3BO3 neutral solutions. The experimental results show that adding NaOH and Na3PO4 in boric acid solution significantly affects the occurrence probability of spontaneous steam explosion, because of the presence of PO43− and H+ ions. When different solutions have equivalent concentrations of H3BO3, the peak pressure values of the spontaneous steam explosion of Sn droplets are similar among various solutions. Compared with those in DI water, steam explosion in the chemical solutions occurs predominantly within a narrow range of depth from 28 mm to 40 mm and produces a much higher peak pressure. This implies that more energetic steam explosions may occur in the chemical solutions.

  • 13.
    Dong, Shichang
    et al.
    Shanghai Jiao Tong Univ, Sch Nucl Sci & Engn, Shanghai, Peoples R China..
    Gong, Shengjie
    Shanghai Jiao Tong Univ, Sch Nucl Sci & Engn, Shanghai, Peoples R China..
    Zhang, Botao
    Shanghai Jiao Tong Univ, Sch Nucl Sci & Engn, Shanghai, Peoples R China..
    Xiong, Zhenqin
    Shanghai Jiao Tong Univ, Sch Nucl Sci & Engn, Shanghai, Peoples R China..
    Yuan, Yidan
    China Nucl Power Engn Co Ltd, Beijing, Peoples R China..
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Theoretical model for subcooled upward flow boiling heat transfer and critical heat flux for an inclined downward heated surface2023In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 213, article id 124351Article in journal (Refereed)
    Abstract [en]

    The in-vessel retention system and ex-vessel retention system are very important to the safety of nu-clear power plants under severe accidents. While the success of such safety systems relies on well un-derstanding the corresponding physical mechanisms of boiling heat transfer and critical heat flux (CHF). Challenges till remain in accurately predicting the subcooled flow boiling curve especially in the low-pressure and low-flow conditions due to its complex boiling phenomenon. The present study introduces a theoretical model to predict the boiling curve and critical heat flux for subcooled flow boiling in in-clined downward heated rectangular channel. The proposed model well estimates the transition from forced convection, isolated bubble nucleate boiling to fully developed boiling regime by considering the growth and interaction of bubbles. Through probability analysis of bubbles' interaction, the proportion of heat flux in different boiling regimes is determined. In addition, the flow boiling CHF is predicted based on the probability analysis of dry spots. The new model is validated by the subcooled flow boil-ing experiments with vertical single-side heated channel under low-pressure and low-flow conditions. The predicted boiling curves are consistent with experimental results corresponding to different thermal-hydraulic parameters, such as pressure, mass flux, inlet subcooling and wall wettability (hydrophilic and hydrophobic), and the prediction error of CHF is within & PLUSMN;15%. Furthermore, the inclination effect on CHF is validated by the subcooled flow boiling experiments in inclined channel with the inclination angle varying from 0 & DEG; to 90 & DEG;, which shows the good applicability of the developed model. 

  • 14. Dovic, D.
    et al.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Svaic, S.
    Generalized correlations for predicting heat transfer and pressure drop in plate heat exchanger channels of arbitrary geometry2009In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 52, no 19-20, p. 4553-4563Article in journal (Refereed)
    Abstract [en]

    Characteristics of the flow in chevron plate heat exchangers are investigated through visualization tests of channels with beta = 28 degrees and beta = 61 degrees. Mathematical model is then developed with the aim of deriving correlations for prediction off and Nu for flow in channels of arbitrary geometry (beta and 1511). Thermal and hydraulic characteristics are evaluated using analytical solutions for the entrance and fully developed regions of a sinusoidal duct adapted to the basic single cell. The derived correlations are finally adjusted so as to agree with experimental results from tests on channels with beta = 28 degrees and beta = 65 degrees. f and Nu calculated by the presented correlations are shown to be consistent with experimental data from the literature at Re = 2-10,000, beta = (15-67)degrees and b/l = 0.26-0.4.

  • 15.
    Fan, Wenyuan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Li, Haipeng
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering. Warsaw Univ Technol, Inst Heat Engn, 21-25 Nowowiejska St, PL-00665 Warsaw, Poland..
    A study of rewetting and conjugate heat transfer influence on dryout and post-dryout phenomena with a multi-domain coupled CFD approach2020In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 163, article id 120503Article in journal (Refereed)
    Abstract [en]

    In the present study, a multi-domain coupled computational fluid dynamics (CFD) approach is developed for the modeling of dryout and post-dryout heat transfer. For the fluid part, the thin film and gas core are modeled by the liquid film model and two-fluid model, respectively. For the solid part, the heating process is modeled by either using a constant heat source or solving the Joule heating problem. The fluid-solid conjugate heat transfer is calculated by using carefully designed coupling schemes which can automatically determine the operation mode for pre- and post-dryout regions. Unlike standalone simulations where only the inner wall temperature is predicted, coupled simulations are able to predict the outer wall temperature, allowing a direct comparison with experiments. Simulations were carried out for a wide range of flow conditions and validated against the corresponding steady state experiments. By newly introducing a film rewetting model, the current CFD code is capable of simulating the transient behavior of dryout. With the rewetting model, the coupled code successfully predicted the dryout hysteresis.

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  • 16. Fang, Xin
    et al.
    Ding, Qing
    Fan, Li-Wu
    Lu, Hai
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. Yunnan Electric Power and Research Institute (Group)Kunming, China.
    Yu, Zi-Tao
    Effects of inclusion size on thermal conductivity and rheological behavior of ethylene glycol-based suspensions containing silver nanowires with various specific surface areas2015In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 81, p. 554-562Article in journal (Refereed)
    Abstract [en]

    This work is concerned with the size effects of Ag nanowires on thermal conductivity and rheological behavior of EG-based suspensions. The influences of inclusion concentration and temperature on the thermophysical properties of specimens containing three types of Ag nanowires were also investigated. It was shown that the measured thermal conductivity of EG-based suspensions increased with the rising temperature and loading. Besides, the relative enhancement in thermal conductivity exhibited a linear relationship with respect to the specific surface area of Ag nanowires. A theoretical approach was developed to predict the effective thermal conductivity of suspensions containing nanowires by introducing liquid layer into account. The Ag nanowires/EG interface thermal resistances were extracted from the experimental results, which ranged from 2.0 x 10(8) to 5 x 10(8) m(2) K/W. Furthermore, a comparative study revealed the excellent performance of Ag nanowires used in present work on improving thermal conductivity compared with the reported studies. Finally, the presence of Ag nanowires with the highest aspect ratio (250) was concluded as the main explanation of a noticeable rise in dynamic viscosity and non-Brownian fluid behavior of EG-based suspensions at the highest loading (10 mg/mL).

  • 17.
    Ghalambaz, Mohammad
    et al.
    Ton Duc Thang Univ, Metamat Mech Biomech & Multiphys Applicat Res Grp, Ho Chi Minh City, Vietnam.;Ton Duc Thang Univ, Fac Appl Sci, Ho Chi Minh City, Vietnam..
    Mehryan, S. A. M.
    Islamic Azad Univ, Yasooj Branch, Young Researchers & Elite Club, Yasuj, Iran..
    Mozaffari, Masoud
    Islamic Azad Univ, Dept Mech Engn, Najafabad Branch, Najafabad, Iran..
    Zadeh, Seyed Mohsen Hashem
    Shahid Chamran Univ Ahvaz, Dept Mech Engn, Ahwaz, Iran..
    Saffari Pour, Mohsen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Shahid Bahonar Univ Kerman, Dept Mech Engn, Kerman, Iran..
    Study of thermal and hydrodynamic characteristics of water-nano-encapsulated phase change particles suspension in an annulus of a porous eccentric horizontal cylinder2020In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 156, article id 119792Article in journal (Refereed)
    Abstract [en]

    In this paper, the thermal and hydrodynamic characteristics of a suspension with water-Nano-Encapsulated Phase Change Material (NEPCM) in an annulus of a porous eccentric horizontal cylinder are investigated. The NEPCM particles have a core-shell structure and stability suspended in water. Hence, the particles, along with the liquid, could freely circulate inside the annuli of the horizontal cylinder due to the buoyancy forces. The cores of these particles are made from a Phase Change Material (PCM). Moreover, such cores are in a continuous exchange of heat transfer between the solid and liquid phases. The heat transfer is acting in a combination of absorption, storage, and release mechanisms. The governing equations for the fluid motions and conservation of energy could be written in partial differential forms and by using the appropriate non-dimensional variables converted into non-dimensional ones. Then, the numerical approach is applied by implementing the finite element method (FEM) to solve such equations iteratively. The impact of various non-dimensional parameters including the fusion temperature, Stefan number, Rayleigh number, Darcy number, the volume fraction of nanoparticles, and eccentricity of the inner cylinder is addressed on the flow and heat transfer. It is observed that the most favourable fusion temperature ranges for the maximum heat transfer rate vary as a function of the Rayleigh number. In addition, the heat transfer rate can be enhanced by applying the phase change core of nanoparticles.

  • 18. Gong, S.
    et al.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Wang, C.
    Mei, Y.
    Gu, H.
    An investigation on dynamic thickness of a boiling liquid film2015In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 90, p. 636-644Article in journal (Refereed)
    Abstract [en]

    Motivated by understanding the micro-hydrodynamics of boiling heat transfer and the mechanism of critical heat flux (CHF) occurrence, the present study is to investigate the boiling phenomenon in a liquid film whose dynamic thickness is recorded by a confocal optical sensor with the measurement accuracy of micrometres, while the bubble dynamics of the boiling in the film is visualized by a high-speed photography. This paper is focused on a statistical analysis of the measured thickness signals for the boiling condition ranging from low heat flux to high heat flux (near or at CHF). The dynamic thickness of liquid film appears oscillating with peak values, resulting from the liquid film movements due to nucleation of bubble(s) and its growth and rupture. The statistical analysis in a certain period indicates there emerge three distinct liquid film thickness ranges: 0-50 μm, 50-500 μm and 500-2500 μm, seemingly corresponding to the microlayer, macrolayer and bulk layer. With increasing heat flux to a specific extent, the bulk layer disappears, and then the macrolayer gradually decreases to ∼105 μm, beyond which the liquid film may lose its integrity and CHF occurs at 1.563 MW/m2.

  • 19. Gong, S.
    et al.
    Mei, Y.
    Amin, M. Y.
    Zhang, B.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Orientation effect on heat transfer coefficient of a downward surface for flow boiling in a rectangular channel under low flow rate2020In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 153, article id 119594Article in journal (Refereed)
    Abstract [en]

    Natural convection boiling in channel with Arc-Shaped will be encountered in the IVR-ERVC (In-Vessel Retention measure by External Reactor Vessel Cooling) system in nuclear power plant under severe accident. The flow and heat transfer characters in this situation is simulated by flow boiling of deionized water in an inclined rectangular channel under low flow rates. This paper aims to separate various parameters (such as orientation, mass flow rate and inlet quality, etc.) to investigate their individual effects on heat transfer coefficient (HTC) in a rectangular channel with cross section of 17 mm × 10 mm. By using a preheater at the inlet of the rectangular channel, the inlet quality could be controlled and the two-phase flow situation could be observed before the fluids entering into the main heater region on one side of the channel wall in downstream. Thus the characteristics of HTC on the main heater could be investigated at different flow patterns. The channel orientations vary from 15 to 90°, the mass flow rates vary from 110 to 288 kg/(m2s) and the qualities vary from 0.003 to 0.036, respectively. Experimental results show that the mass flow rate and quality effects on the HTC are very weak in this study. However, the orientation angle effect on HTC shows an transition region within 45°~60°, while it slowly changes when the orientation angle is smaller than 45° and bigger than 60°. Such tendency could be well formulated by the error function. Compared with different empirical formulas of saturated boiling HTC, it is found that the Liu & Winterton correlation can well predict the experimental HTC results in 90° orientation channel. Based on such correlation and coupled with the error function, a new model was developed by considering the orientation effect, which has an error of ±15% comparing with the experimental data.

  • 20.
    Gong, Shengjie
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Dinh, Truc-Nam
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    An experimental study of rupture dynamics of evaporating liquid films on different heater surfaces2011In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 54, no 7-8, p. 1538-1547Article in journal (Refereed)
    Abstract [en]

    Experimental data were obtained to reveal the complex dynamics of thin liquid films evaporating on heated horizontal surfaces, including formation and expansion of dry spots that occur after the liquid films decreased below critical thicknesses. The critical thickness of water film evaporating on various material surfaces is measured in the range of 60-150 mu m, increasing with contact angle and heat flux while decreasing with thermal conductivity of the heater material. In the case of hexane evaporating on a titanium surface, the liquid film is found resilient to rupture, but starts oscillating as the averaged film thickness decreases below 15 mu m.

  • 21. Gong, Shengjie
    et al.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Gu, Hanyang
    An experimental investigation on bubble dynamics and boiling crisis in liquid films2014In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 79, p. 694-703Article in journal (Refereed)
    Abstract [en]

    This paper presents an experimental study of boiling and boiling crisis in a liquid film on a heater surface. The critical heat flux (CHF) values obtained in the present experiment mirror that of pool boiling, irrespective of initial liquid film thickness and liquid supply rate in the liquid film boiling case. This observation reinforces to the "scale separation" concept that high-heat-flux boiling and burnout are governed by micro-hydrodynamics in the liquid film on the heater surface. In addition to the CHF data, evolutions of bubbles and dry spots in the boiling liquid film are captured by means of high-speed high-resolution video camera. The dry spots were observed over surface heat flux ranging from 0.3 MW/m(2) to CHF, typically covering an area less than 10% of the heater surface. Three types of dry spot evolution are observed: (1) under the low heat flux, dry spots are rewetted by receding water dam upon rupture of corresponding bubbles; (2) as the heat flux reaches 1.25 MW/m(2), dry spots rewetting is additionally aided by liquid flow driven by growth of bubbles nucleated in the vicinity; (3) upon approaching the CHF, dry spot(s) cannot be rewetted anymore and expand laterally, leading to boiling crisis (burnout of the heater surface). The richness of observations and characterization of micro-hydrodynamics in the present study further demonstrates that observations and measurements on boiling liquid films provide a paramount window for investigation and understanding of physical mechanisms of boiling and boiling crisis.

  • 22.
    Haugen, Nils Erland L.
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. SINTEF Energy Res, N-7465 Trondheim, Norway..
    Kruger, Jonas
    SINTEF Energy Res, N-7465 Trondheim, Norway..
    Aarnes, Jorgen R.
    Norwegian Univ Sci & Technol, Dept Energy & Proc Engn, Kolbjorn Hejes Vei 1B, NO-7491 Trondheim, Norway..
    Karchniwy, Ewa
    Norwegian Univ Sci & Technol, Dept Energy & Proc Engn, Kolbjorn Hejes Vei 1B, NO-7491 Trondheim, Norway.;Silesian Tech Univ, Inst Thermal Technol, Konarskiego 22, PL-44100 Gliwice, Poland..
    Klimanek, Adam
    Silesian Tech Univ, Inst Thermal Technol, Konarskiego 22, PL-44100 Gliwice, Poland..
    Thermophoresis and its effect on particle impaction on a cylinder for low and moderate Reynolds numbers2021In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 181, article id 121996Article in journal (Refereed)
    Abstract [en]

    The effect of thermophoresis on the impaction of particles on a cylinder is investigated for different particle sizes, particle conductivities, temperature gradients and for Reynolds numbers between 100 and 1600. This is the first such study performed using Direct Numerical Simulations (DNS), where all temporal and spatial scales of the fluid are resolved. Simulations are performed using the Pencil Code, a high-order finite difference code with an overset-grid method precisely simulating the flow around the cylinder. The ratio of particles impacting the cylinder to the number of particles inserted upstream of the cylinder is used to calculate an impaction efficiency. It is found that both the particle conductivity and the temperature gradient have a close to linear influence on the particle impaction efficiency for small particles. Higher Reynolds numbers result in higher impaction efficiency for middle-sized particles, while the impaction efficiency is smaller for smaller particles. In general, it is found that thermophoresis only has an effect on the small particles, while for larger particles the impaction is dominated by inertial impaction. An algebraic model is presented that predicts the effect of the thermophoretic force on particle impaction on a cylinder. The model is developed based on fundamental principles and validated against the DNS results, which are faithfully reproduced. As such, this model can be used to understand the mechanisms behind particle deposition due to the thermophoretic force, and, more importantly, to identify means by which the deposition rate can be reduced. This is relevant for example in order to minimise fouling on super-heater tube bundles in thermal power plants.

  • 23.
    Huang, Y.
    et al.
    School of Energy and Power Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, China.
    Ge, F.
    School of Energy and Power Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, China.
    Wang, Cong
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
    Hu, Z.
    School of Energy and Power Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, China.
    Numerical study on the heat and mass transfer characteristics of the open-type cross-flow heat-source tower at low ambient temperature2019In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 145, article id 118756Article in journal (Refereed)
    Abstract [en]

    The heat-source tower heat pump (HTHP) has the advantage in preventing frosting and efficiently absorbing heat from the air in winter. Due to the low air humidity in low temperature environment (less than 0 °C), the latent heat exchange between the antifreeze solution and air is a key factor affecting the performance of HTHP. In this paper, a mathematical prediction model is established to investigate the heat and mass transfer characteristics of the heat-source tower (HST) in low temperature environment. It is found that the air temperature can be lower than the corresponding solution temperature in certain areas of HST when the inlet air-solution temperature difference is very small. Under the condition of the average heat transfer temperature difference of 5 °C, there is no significant reduction in the heat transfer when the ambient temperature drops from 0 °C to −15 °C, and the latent heat ratio is 25% and 50% at the ambient temperature of −15 °C and 0 °C respectively. The relationships between the optimum liquid-to-gas ratio of HST and the operation parameters of air and solution are also studied. The results show that air temperature, solution temperature and solution mass concentration have influences on the optimal liquid-to-gas ratio, whereas air relative humidity has no effect. This paper concludes that the latent heat has a significant impact on the heat transfer. A great amount of heat can be transferred from the air to the solution in HST by adjusting and optimizing the operation parameters in low temperature environment.

  • 24.
    Jeon, Joongoo
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. Graduate School of Integrated Energy-AI, Jeonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju 54896, Republic of Korea.
    Lee, Juhyeong
    Department of Nuclear Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Republic of Korea.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Kim, Sung Joong
    Department of Nuclear Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Republic of Korea; Institute of Nano Science & Technology, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Republic of Korea.
    Residual-based physics-informed transfer learning: A hybrid method for accelerating long-term CFD simulations via deep learning2024In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 220, article id 124900Article in journal (Refereed)
    Abstract [en]

    While a big wave of artificial intelligence (AI) has propagated to the field of computational fluid dynamics (CFD) acceleration studies, recent research has highlighted that the development of AI techniques that reconciles the following goals remains our primary task: (1) accurate prediction of unseen (future) time series in long-term CFD simulations (2) acceleration of simulations (3) an acceptable amount of training data and time (4) within a multiple PDEs condition. In this study, we propose a residual-based physics-informed transfer learning (RePIT) strategy to achieve these four objectives using ML-CFD hybrid computation. Our hypothesis is that long-term CFD simulation is feasible with the hybrid method where CFD and AI alternately calculate time series while monitoring the first principle's residuals. The feasibility of RePIT strategy was verified through a CFD case study on natural convection. In a single training approach, a residual scale change occurred around 100th timestep, resulting in predicted time series exhibiting non-physical patterns as well as a significant deviations from the ground truth. Conversely, RePIT strategy maintained the residuals within the defined range and demonstrated good accuracy throughout the entire simulation period. The maximum error from the ground truth was below 0.4 K for temperature and 0.024 m/s for x-axis velocity. Furthermore, the average time for 1 timestep by the ML-GPU and CFD-CPU calculations was 0.171 s and 0.015 s, respectively. Including the parameter-updating time, the simulation was accelerated by a factor of 1.9. In conclusion, our RePIT strategy is a promising technique to reduce the cost of CFD simulations in industry. However, more vigorous optimization and improvement studies are still necessary.

  • 25.
    Kaern, Martin Ryhl
    et al.
    Tech Univ Denmark, Dept Mech Engn, Nils Koppels Alle Bygn 403, DK-2800 Lyngby, Denmark..
    Markussen, Wiebke Brix
    Tech Univ Denmark, Dept Mech Engn, Nils Koppels Alle Bygn 403, DK-2800 Lyngby, Denmark..
    Meyer, Knud Erik
    Tech Univ Denmark, Dept Mech Engn, Nils Koppels Alle Bygn 403, DK-2800 Lyngby, Denmark..
    Elmegaard, Brian
    Tech Univ Denmark, Dept Mech Engn, Nils Koppels Alle Bygn 403, DK-2800 Lyngby, Denmark..
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Experimental comparison and visualization of in-tube continuous and pulsating flow boiling2018In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 125, p. 229-242Article in journal (Refereed)
    Abstract [en]

    This experimental study investigated the application of fluid flow pulsations for in-tube flow boiling heat transfer enhancement in an 8 mm smooth round tube made of copper. The fluid flow pulsations were introduced by a flow modulating expansion device and were compared with continuous flow generated by a stepper-motor expansion valve in terms of the time-averaged heat transfer coefficient. The cycle time ranged from 1 s to 7 s for the pulsations, the time-averaged refrigerant mass flux ranged from 50 kg m(-2) s(-1) to 194 kg m(-2) and the time-averaged heat flux ranged from 1.1 kW m(-2) to 30.6 kW m(-2). The time-averaged heat transfer coefficients were reduced from transient measurements immediately downstream of the expansion valves with 2 K and 20 K subcooling upstream, resulting in inlet vapor qualities at 0.05 and 0.18, respectively, and covered the saturated flow boiling range up to the dry-out inception. Averaged results of the considered range of vapor qualities, refrigerant mass flux and heat flux showed that the pulsations at low cycle time (1 s) improved the time-averaged heat transfer coefficients by 5.6% and 2.2% for the low and high subcooling, respectively. However, the pulsations at high cycle time (7 s) reduced the time-averaged heat transfer coefficients by 1.8% and 2.3% for the low and high subcooling, respectively, due to significant dry-out when the flow-modulating expansion valve was closed. Furthermore, the flow pulsations were visualized by high-speed camera to assist in understanding the time-periodic flow regimes and the effect they had on the heat transfer performance.

  • 26.
    Li, Haipeng
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Prediction of dryout and post-dryout heat transfer using a two-phase CFD model2016In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 99, p. 839-850Article in journal (Refereed)
    Abstract [en]

    This study focuses on development of an integrated CFD model for diabatic high quality two-phase flow including tarns-dryout regions from annular-mist regime to mist regime. One unified three-field CFD model accounting for droplets, gas, and liquid film was developed to simulate both pre and post dryout regions, with local models to determine the dryout occurrence. The thin liquid film model was coupled to the gas core flow model, which is described using the Eulerian-Eulerian approach. For the post-dryout region, the various heat and mass transfer mechanisms between the wall, the gas phase, and the droplets were identified, including the wall-gas convective heat transfer, the droplet evaporation, the droplet-wall direct contact heat transfer and the thermal radiation, to calculate the temperature of the wall and the fluid. Of the most interests, dryout location and wall temperature measurements from a post-dryout heat transfer experiment have been used for the validation. Simulation results show that the dramatic temperature excursion could be well captured using current models. Nevertheless, more work will be continued to improve the accuracy of the results.

  • 27.
    Lupo, Giandomenico
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Duwig, Christophe
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Uncertainty quantification of multispecies droplet evaporation models2020In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 154, article id 119697Article in journal (Refereed)
    Abstract [en]

    Droplet evaporation is handled in general purpose simulations of dispersed flows with the standard semi-empirical zero-dimensional droplet evaporation model. It relies on a number of model parameters, which can be subject to uncertainty. To the knowledge of the authors, the present work is the first uncertainty quantification and sensitivity study of droplet evaporation models. We study the effect of the parameter uncertainties, by performing uncertainty analysis and Monte Carlo variance based sensitivity analysis. The important case of multispecies droplet evaporation is covered. The analysis of the distribution statistics allows us to identify the prevailing trends of the model output when subject to uncertain input parameters. The individual contributions of the model parameters to the variance are ranked in order of importance. Overall, the results provide useful guidelines for the use of the droplet evaporation model in calculations, under different conditions. The identification of evaporation regimes, where different sets of model parameters become important, is also valuable in aiding the design and execution of droplet evaporation experiments.

  • 28.
    Lupo, Giandomenico
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Gruber, Andrea
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Duwig, Christophe
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Direct numerical simulation of spray droplet evaporation in hot turbulent channel flow2020In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 160, article id 120184Article in journal (Refereed)
    Abstract [en]

    We perform a direct numerical simulation (DNS) of 14081 "cold" spherical droplets evaporating in a "hot" fully-developed turbulent channel flow. This effort is the first extensive computation that employs four-way coupling of the droplet motion with the turbulent carrier phase and interface-resolved evaporation dynamics, for a flow configuration that approaches conditions encountered in spray combustion applications. The complex interaction of momentum, heat, species transfer and phase change thermodynamics is explored. Large-scale droplet motion, modulation of the carrier phase turbulence, and influence of the mean and turbulent mass transport on the evaporation dynamics are observed and quantified. Based on the data set, phenomenological explanations of the shear-induced migration of the dispersed phase and of the effect of turbulent mass transport on the evaporation are provided. The transient nature of the DNS is exploited to generate a novel database that samples a range of turbulence and evaporation timescales, from which a model for the enhancement of the evaporation rate by the ambient turbulence is extracted. 

  • 29.
    Lupo, Giandomenico
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Niazi Ardekani, Mehdi
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. Norwegian Univ Sci & Technol NTNU, Dept Energy & Proc Engn, Stockholm, Sweden..
    Duwig, Christophe
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    An Immersed Boundary Method for flows with evaporating droplets2019In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 143, article id 118563Article in journal (Refereed)
    Abstract [en]

    We present a new Immersed Boundary Method (IBM) for the interface resolved simulation of spherical droplet evaporation in gas flow. The method is based on the direct numerical simulation of the coupled momentum, energy and species transport in the gas phase, while the exchange of these quantities with the liquid phase is handled through global mass, energy and momentum balances for each droplet. This approach, applicable in the limit of small spherical droplets, allows for accurate and efficient phase coupling without direct solution of the liquid phase fields, thus saving computational cost. We provide validation results, showing that all the relevant physical phenomena and their interactions are correctly captured, both for laminar and turbulent gas flow. Test cases include fixed rate and free evaporation of a static droplet, displacement of a droplet by Stefan flow, and evaporation of a hydrocarbon droplet in homogeneous isotropic turbulence. The latter case is validated against experimental data, showing the feasibility of the method towards the treatment of conditions representative of real life spray fuel applications.

  • 30.
    Lyu, Sixiang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Wang, Cheng
    Zhang, Chuanyu
    Royon, Laurent
    Guo, Xiaofeng
    Experimental characterization of a novel soft polymer heat exchanger for wastewater heat recovery2020In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 161, article id 120256Article in journal (Refereed)
    Abstract [en]

    Wastewater released from showers, sinks, and washers contains a considerable amount of waste heat that can be recovered by using a heat exchanger. Conventional metal heat exchangers for wastewater heat recovery have common problems of corrosion, fouling and clogging, which makes it necessary to develop a new type of heat exchanger for such low-grade thermal energy recovery applications. This study deals with a novel patented polymer heat exchanger (WO2020049233A1) made of soft polyurethane tubes that are capable of oscillation once subjected to external forces. Laboratory tests coupled with theoretical analyses show a stable global heat transfer coefficient of 100-110 W/m(2) K, achieving 67-92% of the performance of titanium-, aluminum-, and copper-made heat exchangers with the same configuration. It further reveals that the performance of the soft heat exchanger can be enhanced by 30% when it is under oscillation. In addition, the external convective thermal resistance appears to be the dominant one instead of heat conduction through the wall material. The special operating condition of heat recovery from a sewer pipeline makes the polymer heat exchanger particularly adapted with its equivalent thermal performance but advantages of high flexibility, modularity, and low cost. 

  • 31. Majlesara, M.
    et al.
    Abouali, O.
    Kamali, R.
    Niazi Ardekani, Mehdi
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Numerical study of hot and cold spheroidal particles in a viscous fluid2020In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 149, article id 119206Article in journal (Refereed)
    Abstract [en]

    The gravity-driven motion of rigid particles with a temperature difference with respect to the surrounding viscous fluid is relevant in many natural and industrial processes, yet this has mainly been investigated for spherical particles. In this work we study the influence of the Grashof number (Gr) on the settling velocity and the drag coefficient CD of a single spheroidal particle of different aspect ratios (1/3, 1 and 3). The discrete forcing immersed boundary method (IBM) is employed to represent the fluid-solid interaction in both momentum and temperature equations, while the Boussinesq approximation is used for the coupling of momentum and temperature. The simulations show that the drag coefficient of any spheroidal particle below the onset of secondary motion can be predicted by the results of the settling spheres at the desired Grashof number as the main effect of the particle shape at low Galileo number (Ga) and sufficiently small Gr/Ga2 is found to be the change in the frontal area of the particle. Furthermore, we identify the regions of stable sedimentation (vertical path) in the Ga−Gr/Ga2 plane for the 3 particle shapes, investigated in this study. We show that the critical Ga beyond which the particle exhibits the zigzagging motion, is considerably smaller for oblate particles in comparison to prolate ones at low Gr/Ga2. However, both spheroidal shapes indicate a similar behavior as Gr/Ga2 increases beyond 0.5. 

  • 32. Motahar, Sadegh
    et al.
    Alemrajabi, Ali A.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Experimental investigation on heat transfer characteristics during melting of a phase change material with dispersed TiO2 nanoparticles in a rectangular enclosure2017In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 109, p. 134-146Article in journal (Refereed)
    Abstract [en]

    This paper presents an experimental investigation on the melting process of n-octadecane as a phase change material (PCM) with dispersed titanium oxide (TiO2) nanoparticles. Experiments were performed in a rectangular enclosure heated at constant rates from one vertical side corresponding to Rayleigh numbers in the range 0.57 x 10(8)-43.2 x 10(8) and Stefan number in the range 5.7-23.8. The rheological behavior of liquid PCM/TiO2 at the mass fractions of 2 and 4% tended to Bingham fluids, thus the melting experiment was conducted for Bingham numbers in the range 0-31.1. Heat transfer during melting was characterized by visualizing the solid-liquid interface as well as recording the temperature distribution in the enclosure. Experimental results showed that at the initial stage of melting, heat transferred by conduction, and at later times, natural convection dominated heat transfer. Dispersing TiO2 nanoparticles led to increase in Bingham number and consequently the natural convection and melting rate deteriorated. Two correlations were proposed to predict the Nusselt number and melted volume fraction as a function of Fourier number, Rayleigh number, Stefan number, Bingham number and mass fraction of nanoparticles.

  • 33.
    Nilsson, Fritjof
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Moyassari, Ali
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Bautista, Angela
    E2F, Plaza Benjamin Palencia 2-3,Entreplata 5, Albacete 02006, Spain..
    Castro, Abraham
    E2F, Plaza Benjamin Palencia 2-3,Entreplata 5, Albacete 02006, Spain..
    Arbeloa, Ignacio
    Amayuelas SL, C Orense 27,Esc B 5 Drch, Madrid 28020, Spain..
    Jarn, Mikael
    RISE Res Inst Sweden, Div Biosci & Mat, Box 5607, SE-11486 Stockholm, Sweden..
    Lundgren, Urban
    RISE Res Inst Sweden, Div Safety & Transport, Elect, Brinellgatan 4,Box 857, SE-50115 Boras, Sweden..
    Welinder, Jan
    RISE Res Inst Sweden, Div Safety & Transport, Elect, Brinellgatan 4,Box 857, SE-50115 Boras, Sweden..
    Johansson, Kenth
    RISE Res Inst Sweden, Div Biosci & Mat, Box 5607, SE-11486 Stockholm, Sweden..
    Modelling anti-icing of railway overhead catenary wires by resistive heating2019In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 143, article id 118505Article in journal (Refereed)
    Abstract [en]

    Aggregation of ice on electrical cables and apparatus can cause severe equipment malfunction and is thus considered as a serious problem, especially in arctic climate zones. In particular, cable damage caused by ice accumulation on railway catenary wires is in wintertime a common origin for delayed trains in the northern parts of Europe. This study examines how resistive heating can be used for preventing formation of ice on metallic, non-insulated electrical cables. The heat equation and the Navier Stokes equations were solved simultaneously with FEM in 3D in order to predict the cable temperature as function of external temperature, applied voltage, wind speed, wind direction, and heating time. An analytical expression for the heat transfer coefficient was derived from the FEM simulations and it was concluded that the influence of wind direction can typically be neglected. Experimental validation measurements were performed on Kanthal cables in a climate chamber, giving temperature increase results in good agreement with the simulation predictions. The resistive heating efficiency, i.e. the ratio between applied electrical energy and resulting thermal energy, was found to be approximately 68% in this particular study.

  • 34.
    Ningegowda, Bittagowdanahalli M.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. Univ Perugia, Dept Engn, I-06125 Perugia, Italy..
    Ge, Zhouyang
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Mechanics.
    Lupo, Giandomenico
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Mechanics.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Mechanics. Norwegian Univ Sci & Technol NTNU, Dept Energy & Proc Engn, N-7491 Trondheim, Norway..
    Duwig, Christophe
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Mechanics.
    A mass-preserving interface-correction level set/ghost fluid method for modeling of three-dimensional boiling flows2020In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 162, article id 120382Article in journal (Refereed)
    Abstract [en]

    We present an efficient method for the direct numerical simulation of three-dimensional (3D) boiling flows. The liquid-vapor interface dynamics is captured using an interface-correction level set method, modified to account for the interface heat and mass transfer due to phase change. State-of-the-art computational techniques, such as the fast pressure-correction and ghost-fluid methods, are implemented to accurately solve the coupled thermo-fluid problem involving large density contrasts and jump conditions. The solver is thoroughly validated against four benchmark cases with increasing complexity, which show better mass conservation properties than traditional level set methods, thus allowing for coarser grid resolutions and lower computational costs. We further demonstrate our method by simulating two realistic 3D boiling flows in greater details. In the first case, a saturated film boiling of water vapor at near critical conditions over a horizontal hot flat plate is considered. The results are analyzed by comparing the transient evolution of the interface morphology, temperature distribution, space and time averaged Nusselt numbers obtained from numerical simulations with the semi-empirical correlation of Berenson and existing numerical literature. In the second case, we simulate the condensation and buoyancy-driven motion of a single spherical water vapor bubble at different subcooled liquid temperatures and saturation pressures. We find opposite trends of the condensation rate and the bubble rising velocity when the degree of subcooling is increased, and an increase of the condensation rate at lower saturation pressures, due to variation of the thermophysical properties.

  • 35.
    Nosko, Oleksii
    Saitama University, Japan .
    Partition of friction heat between sliding semispaces due to adhesion: deformational heat generation2013In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 64, p. 1189-1195Article in journal (Refereed)
    Abstract [en]

    Analytical expressions of heat-partition coefficient and contact temperatures for two sliding semispaces with account for adhesion-deformational heat generation and contact heat exchange have been obtained. The rate of deformational heat generation is assumed to decay exponentially with increase of distance from the interface. It has been shown that heat-generation configuration and the intensity of contact heat exchange have impact on heat partition only within a transient interval. The features of perfect thermal contact have been analyzed. Perfect thermal contact implies variation of heat partition in time. Heat partition and contact temperature for a semispace, sliding over a semispace with a constant temperature, have been studied. Adhesion-deformational heat generation results in a change of the direction of surface heat flow.

  • 36.
    Parvar, Saeed
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Univ Porto, CEFT, FEUP, Rua Dr Roberto Frias, P-4200465 Porto, Portugal.;INEGI, Campus FEUP,FEUP,Rua Dr Roberto Frias, P-4200465 Porto, Portugal..
    da Silva, Carlos B.
    Univ Lisbon, Inst Super Tecn, IDMEC, LAETA, Lisbon, Portugal..
    Pinho, Fernando
    Univ Porto, CEFT, FEUP, Rua Dr Roberto Frias, P-4200465 Porto, Portugal..
    Thermal boundary layer of laminar flow of dilute polymer solution2022In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 185, article id 122248Article in journal (Refereed)
    Abstract [en]

    The thermal boundary layer flow is a canonical flow with characteristics that are present in most natural and industrial convection flows. An approximate self-similar solution is proposed for the first time for the thermal boundary layer of steady laminar flow of viscoelastic fluids, described by the finitely extensible nonlinear elastic constitutive equation with Peterlin's closure (FENE-P model). This semi-analytical ther-mal solution is obtained by performing an order of magnitude analysis and ensuing simplifications of the governing equations by assuming that the fluid properties are independent of temperature therefore de-coupling the flow governing equations from the energy equation. The effects of viscoelasticity quantified with the Weissenberg number based on the streamwise coordinate (x) (W-ix) up to W-ix = 1 and viscous dissipation (results are presented for Brinkman numbers between-40 and + 40) on thermal boundary layer characteristics are investigated comprehensively for both constant wall temperature and constant wall heat flux. At low elasticity levels (Wi(x) < 0.01 ) the solution exhibits a global self-similar behavior in which flow and thermal quantities collapse on the corresponding Newtonian curves, and the polymer characteristics show a unique behavior if adequately normalized. However, by increasing flow elasticity the unique self-similar behavior of the approximate solution is lost, with the elasticity dependent results exhibiting local variations. In addition, the effects of elasticity are intensified by viscous dissipation. For the present study cases, it is observed that elasticity may change Nusselt numbers by more than 8%, and the thermal boundary layer thickens by up to 10%.

  • 37.
    Rastan, Hamidreza
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. KTH Royal Inst Technol, Dept Energy Technol, SE-10044 Stockholm, Sweden..
    Abdi, Amir
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Hamawandi, Bejan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Ignatowicz, Monika
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Meyer, Josua
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Heat transfer study of enhanced additively manufactured minichannel heat exchangers2020In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 161, article id 120271Article in journal (Refereed)
    Abstract [en]

    Three-dimensional (3D) printing, known as additive manufacturing, provides new opportunities for the design and fabrication of highly efficient industrial components. Given the widespread use of this technique by industries, 3D printing is no longer limited to building prototypes. Instead, small-to-medium scale production units focus on reducing the cost associated with each part. Among the various industrial components that can be developed with this manufacturing technology are heat transfer components such as heat exchangers. To this end, this study investigated the heat transfer characteristics of minichannel-based heat exchangers embedded with longitudinal vortex generators, both experimentally and numerically. Three enhanced prototypes with different vortex generator design parameters and a smooth channel as a reference case were printed with an aluminum alloy (AlSi10Mg) using direct metal laser sintering (DMLS). The rectangular minichannel had a hydraulic diameter of 2.86 mm. Distilled water was used as the test fluid, and the Reynolds number varied from 170 to 1380 (i.e., laminar flow). Prototypes were tested under two different constant heat fluxes of 15 kW m(-2) and 30 k m(-2). The experimental results were verified with a commercial simulation tool, Comsol Multiphysics (R), using the 3D conjugate heat transfer model. In the case of the smooth channel, the experimental results were also compared with well-known correlations in the field. The results showed that 95% and 79% of the experimental data were within 10% of the numerical simulation results and the values from the existing correlations, respectively. For the channel enhanced with the vortex generators, the numerical predictions agreed well with the experimental results. It was determined that the vortex generators can enhance the convective heat transfer up to three times with the designed parameter. The findings from this research underline the potential of additive manufacturing in the development of more sophisticated minichannel heat exchangers.

  • 38.
    Rönnberg, Kristian
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. ABB AB, Corp Res, SE-72226 Västerås, Sweden..
    Duwig, Christophe
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Process Technology.
    Heat transfer and associated coherent structures of a single impinging jet from a round nozzle2021In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 173, article id 121197Article in journal (Refereed)
    Abstract [en]

    The heat transfer arising from an impinging jet at a Reynolds number of 500 0 is studied through LargeEddy Simulation (LES), with special attention on the heat transfer dynamics. The obtained heat transfer and flow fields are decomposed and studied using proper orthogonal decomposition (POD) and extended proper orthogonal decomposition (EPOD). The heat transfer appear to be distributed according to a gamma distribution, in time, with location-dependent shape and scale parameters. The results obtained show that, over time, many locations on the impingement plate experience large over- and undershoots compared to the time-averaged Nusselt number distribution. The POD analysis show that the low order heat transfer modes, while having low relative intensity, are associated with distinct flow features. The flow features are identified by application of EPOD. The two dominant modes are associated with ring-like vortex structures organized concentrically around the impingement point. Reconstruction of the heat transfer field using the three first modes and the mean field show radially outward moving structures with a phase velocity of 0.23 U-b.

  • 39.
    Shen, Biao
    et al.
    Kyushu Univ, Int Inst Carbon Neutral Energy Res WPI 12CNER, Motooka 744, Fukuoka, Fukuoka 8190395, Japan..
    Liu, Jiewei
    KTH. Royal Inst Technol, Dept Mech, S-10044 Stockholm, Sweden..
    Shiomi, Junichiro
    Univ Tokyo, Dept Mech Engn, Hongo 7-3-1, Tokyo 1138656, Japan..
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Do-Quang, Minh
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Kohno, Masamichi
    Kyushu Univ, Int Inst Carbon Neutral Energy Res WPI 12CNER, Motooka 744, Fukuoka, Fukuoka 8190395, Japan.;Kyushu Univ, Dept Mech Engn, Motooka 744, Fukuoka, Fukuoka 8190395, Japan..
    Takahashi, Koji
    Kyushu Univ, Dept Aeronaut & Astronaut, Motooka 744, Fukuoka, Fukuoka 8190395, Japan..
    Takata, Yasuyuki
    Kyushu Univ, Int Inst Carbon Neutral Energy Res WPI 12CNER, Motooka 744, Fukuoka, Fukuoka 8190395, Japan.;Kyushu Univ, Dept Mech Engn, Motooka 744, Fukuoka, Fukuoka 8190395, Japan..
    Effect of dissolved gas on bubble growth on a biphilic surface: A diffuse-interface simulation approach2018In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 126, p. 816-829Article in journal (Refereed)
    Abstract [en]

    In this paper, we numerically study pool boiling of a binary (water and nitrogen) mixture on a surface endowed with a combination of hydrophobicity and hydrophilicity (i.e., the so called biphilic surface). Here we adopt a numerical approach based on the phase field theory, where the vapor-liquid interface is assumed to be of a finite thickness (hence diffusive in nature) and requires no explicit tracking schemes. The theoretical modeling of two-phase heat and mass transfer in water diluted with nitrogen demonstrates the signiant impact of impurities on bubble dynamics. The simulations show that locally high concentrations of nitrogen gas within the vapor bubble is essential to weakening the condensation effect, which results in sustained bubble growth and ultimately (partial) departure from the surface under the artificially enlarged gravity. Simply increasing the solubility of nitrogen in water, however, turns out to be counterproductive because possible re-dissolution of the aggregated nitrogen by the bulk water could deprive the bubble of vital gas contents, leading instead to continuous bubble shrinkage and collapse. Additionally, it is found that with the significant accumulation of nitrogen, the bubble interface is increasingly dominated by a strong interfacial thermocapillary flow due to the Marangoni effect.

  • 40. Shi, K. Z.
    et al.
    Bao, F. L.
    He, N.
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Near-field heat transfer between graphene-Si grating heterostructures with multiple magnetic-polaritons coupling2019In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 134, p. 1119-1126Article in journal (Refereed)
    Abstract [en]

    Near-field thermal radiation (NFTR) between two graphene-covered Si grating (G/Si grating) heterostructures consisting of multilayered G/Si grating cells is investigated, in comparison with that between single-G/Si-grating-cell structures. The calculations are based on the scattering theory utilizing rigorous coupled-wave analysis (RCWA). It is found that strong magnetic polaritons (MPs) can be induced in the single G/Si grating cell, and coupling of multiple MPs can be observed in multilayered G/Si grating heterostructures, which leads to a broader band of high photon-tunnelling probabilities in the phase space. As a result, when the thickness of each grating layer is fixed, the heat flux of the 4-G/Si grating heterostructures, with chemical potential μ = 0.1 eV and grating period L x = 80 nm, is 1.65- and 9.12-fold larger than those of the 1-G/Si grating and only Si grating structures at d = 100 nm, respectively. When the total thickness of the entire G/Si grating heterostructure is fixed, the 1-G/Si grating model performs better than 2- or 4-G/Si grating models because higher loss inherited from additional graphene sheets would reduce the momenta of the near-unity energy transmission coefficient in the k-space.

  • 41.
    Straub, Steffen
    et al.
    Karlsruhe Inst Technol, Inst Fluid Mech, D-76131 Karlsruhe, Germany..
    Forooghi, Pourya
    Karlsruhe Inst Technol, Inst Fluid Mech, D-76131 Karlsruhe, Germany..
    Marocco, Luca
    Politecn Milan, Dipartimento Energia, I-20156 Milan, Italy..
    Wetzel, Thomas
    Karlsruhe Inst Technol, Inst Thermal Proc Engn, D-76131 Karlsruhe, Germany..
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Stability, Transition and Control.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Vehicle Engineering and Solid Mechanics, Stability, Transition and Control.
    Frohnapfel, Bettina
    Karlsruhe Inst Technol, Inst Fluid Mech, D-76131 Karlsruhe, Germany..
    The influence of thermal boundary conditions on turbulent forced convection pipe flow at two Prandtl numbers2019In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 144, article id 118601Article in journal (Refereed)
    Abstract [en]

    Different types of thermal boundary conditions are conceivable in numerical simulations of convective heat transfer problems. Isoflux, isothermal and a mixed-type boundary condition are compared by means of direct numerical simulations (for the lowest Reynolds number) and well-resolved large-eddy simulations of a turbulent forced convection pipe flow over a range of bulk Reynolds numbers from Re-b = 5300 to Re-b = 37700, at two Prandtl numbers, i.e. Pr = 0.71 and Pr = 0.025. It is found that, while for Pr = 0.71 the Nusselt number is hardly affected by the type of thermal boundary condition, for Pr = 0.025 the isothermal boundary condition yields approximate to 20% lower Nusselt numbers compared to isoflux and mixedtype over the whole range of Reynolds numbers. A decomposition of the Nusselt number is derived. In particular, we decompose it into four contributions: laminar, radial and streamwise turbulent heat flux as well as a contribution due to the turbulent velocity field. For Pr = 0.71 the contribution due to the radial turbulent heat flux is dominant, whereas for Pr = 0.025 the contribution due to the turbulent velocity field is dominant. Only at a moderately high Reynolds number, such as Re-b = 37700, both turbulent contributions are of similar magnitude. A comparison of first- and second-order thermal statistics between the different types of thermal boundary conditions shows that the statistics are not only influenced in the near-wall region but also in the core region of the flow. Power spectral densities illustrate large thermal structures in low-Prandtl-number fluids as well as thermal structures located right at the wall, only present for the isoflux boundary condition. A database including the first- and second-order statistics together with individual contributions to the budget equations of the temperature variance and turbulent heat fluxes is hosted in the open access repository KITopen (DOI : https: //doi.org/10.5445/IR/1000096346).

  • 42. Utomo, Adi T.
    et al.
    Haghighi, Ehsan B.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Zavareh, Ashkan I. T.
    Ghanbarpourgeravi, Morteza
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Poth, Heiko
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Pacek, Andrzej W.
    The effect of nanoparticles on laminar heat transfer in a horizontal tube2014In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 69, p. 77-91Article in journal (Refereed)
    Abstract [en]

    Heat transfer coefficient in laminar flow of water-based alumina, titania and carbon nanotube nanofluids in a straight pipe with constant heat flux at the wall have been investigated independently by two universities. The nanoparticles affect the thermo-physical properties of the suspensions, however, nanopartides presence and movement due to Brownian diffusion and thermophoresis seemed to have insignificant effect on heat transfer coefficient. The Nusselt number of all investigated nanofluids followed standard heat transfer correlations developed for liquids within +/- 10% suggesting that all investigated nanofluids can be treated as homogenous fluids. Different methods of comparison between heat transfer coefficient in nanofluids and base fluid are also critically discussed.

  • 43.
    Vynnycky, Michael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Process. Univ Limerick, Dept Math & Stat, Math Applicat Consortium Sci & Ind MACSI, Limerick V94 T9PX, Ireland..
    On the local solute redistribution equation of macrosegregation, remelting and the formation of channel segregates2022In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 190, article id 122737Article in journal (Refereed)
    Abstract [en]

    In this paper, we reassess the local solute redistribution equation (LSRE) of macrosegregation which, since it first appeared in 1960s, has served as a cornerstone for understanding the composition variations that occur in the solidification of alloys. We highlight some anomalies in earlier literature, in particular as regards the prediction of remelting as a precursor to the formation of channel segregates (freckles, A-segregates and V-segregates) in casting processes. Also, we suggest extensions to the LSRE for situations where solute diffusion in the solid phase is not negligible, as well as when the mode of solidification is unconsolidated equiaxed dendritic, rather than columnar/consolidated equiaxed dendritic. In addition, the significance of the equation for latter-day numerical computations of macrosegregation is also discussed.

  • 44.
    Vynnycky, Michael
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Casting of Metals.
    Kimura, S.
    Can natural convection alone explain the Mpemba effect?2015In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 80, p. 243-255Article in journal (Refereed)
    Abstract [en]

    The Mpemba effect is popularly summarized by the statement that "hot water can freeze faster than cold water", and has been observed experimentally since the time of Aristotle; however, there remains no definitive explanation for the effect. Here, we consider experimentally and theoretically the freezing of water in a rectangular vessel, with a view to investigating natural convection as a possible mechanism. The experimental and theoretical results are, in general, found to agree well; however, in combination, the results suggest that, whereas natural convection gives the correct general timescale for freezing, supercooling adjusts the actual time required. Moreover, the effect of supercooling leads to a spread in the experimental freezing times, giving results that constitute evidence of the occurrence of the Mpemba effect, even though the model results by themselves do not.

  • 45.
    Vynnycky, Michael
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Kimura, Shigeo
    An analytical and numerical study of coupled transient natural convection and solidification in a rectangular enclosure2007In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 50, no 25-26, p. 5204-5214Article in journal (Refereed)
    Abstract [en]

    The transient process of the solidification of a pure liquid phase-change material in the presence of natural convection in a rectangular enclosure is considered both analytically and numerically. One vertical boundary is held at a temperature below the melting-point of the material, the other above; the horizontal boundaries are both assumed adiabatic. A nondimensional analysis of the problem, principally in terms of the Rayleigh (Ra) and Stefan (St) numbers, indicates that some asymptotic simplification is possible for materials often considered in the literature (water, gallium, lauric acid). This observation suggests a way to simplify the full problem when Ra >> 1 and St << 1, giving a conventional boundary value problem for the liquid phase and pointwise-in-space first-order ODEs for the evolution in time of the solidification front. The method is tested against full 2D finite-element-based transient numerical simulations of solidification. In addition, simpler approaches for determining the average thickness of the solid layer, based on boundary-layer and enclosure flow correlations, are also investigated.

  • 46.
    Vynnycky, Michael
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Casting of Metals.
    Zambrano, M.
    Cuminato, J. A.
    On the avoidance of ripple marks on cast metal surfaces2015In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 86, p. 43-54Article in journal (Refereed)
    Abstract [en]

    A mathematical model is derived for the purposes of predicting how to avoid unwanted defects, known as ripple marks, in the casting of metal ingots; the model is based around the momentum and heat transfer that occurs when a cooling molten metal meniscus rises between two parallel and vertical chill-mould walls. By using asymptotic techniques, the model is reduced systematically to a form that requires the numerical solution of a moving boundary problem involving just one partial differential equation. Numerical results are presented, and the significance of the model for predicting the depth and spacing of ripple marks in the casting of ingots and oscillation marks in continuous casting are discussed.

  • 47.
    Wiberg, Roland
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Faxén Laboratory.
    Lior, N.
    Heat transfer from a cylinder in axial turbulent flows2005In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 48, no 8, p. 1505-1517Article in journal (Refereed)
    Abstract [en]

    Local convective heat transfer coefficients were measured on a two-diameter long cylinder in axial flows of air at conditions unexplored so far, by using thermochromic liquid crystals (TLC) coated on an electrically heated strip-foil consisting bonded to the external surfaces. The Reynolds numbers (Re) based on the cylinder diameter were between 8.9 x 10(4) and 6.17 x 10(5), and the flow in front of the cylinder was modified in some cases by the use of a turbulence generating grid, or by circular disc inserts of two sizes placed upstream of the cylinder. These created a major change in the local convective heat transfer coefficient distribution on the cylinder. Increase of the turbulence intensity from Tu < 0.1% to Tu = 6.7% at the same Re increased the average calculated Nusselt number Nu over the cylinder by 25%, and decreased the Nu non-uniformity over the surface. One of the flow modification inserts also reduced significantly the Nu non-uniformity. The position of flow reattachment was measured using tufts. Our heat transfer data agree well with the small amount if data published of others, when extrapolated to their conditions. Correlations between the Nu and Re in the form Nu = CRee were established and presented for the average Nu on the front, middle and rear cylinder surfaces, and the variation of the local exponent e was shown along the cylinder. Introducing a new technique, a TLC-coated heated flat plate mounted in the flow above the cylinder in the meridional plane was demonstrated to help visualize the flow field above the cylinder. A track of maximum convective coefficients on this plate was found similar in position to the stream line dividing the forward and backward flows in a case measured for the separated flow in a past study.

  • 48. Yakush, S. E.
    et al.
    Kudinov, Pavel
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    On the evaluation of dryout conditions for a heat-releasing porous bed in a water pool2019In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, p. 895-905Article in journal (Refereed)
    Abstract [en]

    This work is motivated by the problem of restraining temperature escalation inside a porous heat-releasing media submerged in a pool of liquid coolant. When coolant temperature reaches saturation, boiling begins in the bulk of the porous bed, with void generation rate determined by the heating power. Amount of void determines hydrostatic pressure difference that drives natural circulation of two-phase flow through the porous material. At a certain critical value of the heat release rate, the driving head cannot overcome drag of the two phase porous media flow, which results in complete evaporation of coolant in some zone. Temperature of material in the dry zone increases significantly due to deterioration of heat exchange with single phase vapor flow in comparison with boiling flow heat transfer. The paper considers the problem of determining the critical conditions for onset of dryout in a heat-releasing porous bed of an arbitrary shape. The well-known one-dimensional problem for a flat top-flooded bed is revisited, and the functional form of the dryout boundary (expressed as the dryout heat flux, DHF) is derived using non-dimensional parameters. Asymptotic behavior of the solution is analyzed, and, by the method of asymptotic interpolation, a surrogate model is proposed consisting of three single-argument, non-dimensional functions. It is shown that such a model provides acceptable accuracy even in the cases where complete similarity of solutions is not achieved. The results obtained provide important insights into the physics of the problem, reduce the number of free parameters, and enable fast evaluation of dryout conditions without the need of numerical solution of algebraic equations involved in the exact formulation. The ultimate goal of the surrogate model development, i.e. its application to multidimensional configurations, is discussed.

  • 49. Yang, Z. L.
    et al.
    Dinh, Truc-Nam
    KTH, Superseded Departments (pre-2005), Physics.
    Nourgaliev, R. R.
    Sehgal, B. R.
    Numerical investigation of bubble growth and detachment by the lattice-Boltzmann method2001In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 44, no 1, p. 195-206Article in journal (Refereed)
    Abstract [en]

    A numerical study has been performed to investigate the characteristics of bubble growth on, and detachment from, an orifice. The FlowLab code, which is based on a lattice-Boltzmann model of two-phase flows, was employed. Macroscopic properties, such as surface tension (a) and contact angle (beta), were implemented through the fluid-fluid (G(sigma)) and fluid-solid (G(t)) interaction potentials. The model was found to possess a linear relation between the macroscopic properties (sigma, beta) and microscopic parameters (G(sigma), G(t)). The separate effects of the body force (gravity), gas injection rate, surface tension, and wettability were analyzed for both horizontal and vertical surfaces. It is shown that results of the lattice-Boltzmann modeling exhibit correct parametric dependencies of the departure diameter of bubbles generated on the horizontal surface on the above factors as previously established in experiments. For the case of bubble growth and departure on the vertical surface, the different effects of hydrodynamic parameters, except gas generation rate, were predicted.

  • 50. Yang, Z. L.
    et al.
    Palm, Björn E.
    KTH, Superseded Departments (pre-2005), Energy Technology.
    Sehgal, B. R.
    Numerical simulation of bubbly two-phase flow in a narrow channel2002In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 45, no 3, p. 631-639Article in journal (Refereed)
    Abstract [en]

    An advanced numerical simulation method on fluid dynamics - lattice-Boltzmann (LB) method is employed to simulate the movement of Taylor bubbles in a narrow channel, and to investigate the flow regimes of two-phase flow in narrow channels under adiabatic conditions. The calculated average thickness of the fluid film between the Taylor bubble and the channel wall agree well with the classical analytical correlation developed by Bretherton. The numerical simulation of the behavior of the flow regime transition in a narrow channel shows that the body force has significant effect on the movement of bubbles with different sizes. Smaller body force always leads to the later coalescence of the bubbles, and decreases the flow regime transition time. The calculations show that the surface tension of the fluid has little effect on the flow regime transition behavior within the assumed range of the surface tension. The bubbly flow with different bubble sizes will gradually change into the slug flow regime. However, the bubbly flow regime with the same bubble size may be maintained if no perturbations on the bubble movement occur. The slug flow regime will not change if no phase change occurs at the two-phase interface.

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