Change search
Refine search result
12345 101 - 150 of 216
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 101.
    Ignatowicz, Monika
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Melinder, Åke
    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.
    MEASUREMENTS OF STANDARD SEAWATER CALLS FOR MINOR ADJUSTMENTS OF SEAWATER ICE SLURRY PROPERTIES2016In: 11TH IIR CONFERENCE ON PHASE CHANGE MATERIALS AND SLURRIES FOR REFRIGERATION AND AIR CONDITIONING / [ed] Kauffeld, M, 2016, p. 162-170Conference paper (Refereed)
    Abstract [en]

    Seawater is the most common fluid on earth and ice generating machines are increasingly used on fishing vessels to produce ice slurry from the seawater with up to 60 % ice to be poured over the catch. In this study, new measurements of thermophysical properties of standard seawater have been carried out to complement a recent literature search made to establish thermophysical property data of seawater as function of salinity and temperature. These single-phase measurements have been made for salinity 20, 30 and 35 g kg(-1) (2.0, 3.0 and 3.5 % total salt content) and include measurements of freezing point, density, dynamic viscosity, thermal conductivity, specific heat capacity and specific enthalpy. The obtained experimental results generally confirm recent literature search and experimental results only call for minor adjustments of viscosity values. Hence, experimental results confirm the following published ice slurry properties: enthalpy, ice fraction and ice slurry density.

  • 102.
    Jarahnejad, Mariam
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Haghighi, Ehsan B.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Nikkam, Nader
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    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.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Experimental investigation on viscosity of water-based Al2O3 and TiO2 nanofluids2015In: Rheologica Acta, ISSN 0035-4511, E-ISSN 1435-1528, Vol. 54, no 5, p. 411-422Article in journal (Refereed)
    Abstract [en]

    This article investigates the influence of temperature, concentration, and size of nanoparticles, and addition of surfactants on dynamic viscosity of water-based nanofluids containing alumina (Al2O3) and titania (TiO2) nanoparticles. Two viscometers, a capillary and a falling ball, were used for the measurements in the temperature range of 20-50 A degrees C and the particle concentration of 3-14.3 wt.%. The results indicate that the viscosity of nanofluids is reduced by increasing the temperature, similar to their base fluids. Moreover, surfactants, which are used to improve the shelf stability of nanofluids, most likely increase their viscosity. The correlations derived from the linear fluid theory such as Einstein and Batchelor, especially for solid concentration above 1.5 wt.% are not accurate to predict viscosity of nanofluids, while the modified Krieger-Dougherty equation estimates viscosity of nanofluids with acceptable accuracy in a specific range of solid particle size to aggregate size.

  • 103.
    Jonsson, Hans
    et al.
    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.
    Experimental Comparison of Different Heat Sink Designs for Cooling of Electronics1996In: ASME HTD, 1996, Vol. 329, p. 27-34Conference paper (Refereed)
  • 104.
    Jonsson, Hans
    et al.
    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.
    Influence of Airflow Bypass on the Thermal Performance and Pressure Drop of Plate Fin and Pin Fin Heat Sinks for Electronics Cooling1997In: Eurotherm, 1997, Vol. 58, p. 44-50Conference paper (Refereed)
  • 105.
    Jonsson, Hans
    et al.
    KTH, Superseded Departments, Energy Technology.
    Palm, Björn
    KTH, Superseded Departments, Energy Technology.
    Thermal and hydraulic behavior of plate fin and strip fin heat sinks under varying bypass conditions2000In: IEEE transactions on components and packaging technologies (Print), ISSN 1521-3331, E-ISSN 1557-9972, Vol. 23, no 1, p. 47-54Article in journal (Refereed)
    Abstract [en]

    Tests have been conducted in a wind tunnel with nine heat sinks of three different types including plate fin heat sinks and strip fin heat sinks arranged in both inline and staggered arrays. For each type, tests were run with fin heights (H) of 10, 15, and 20 mm while the heat sink width (B) was kept constant and equal to 52.8 mm. The width of the wind tunnel duct (CB) was varied in such a way that results were obtained for B/CB = 0.84, 0.53, and 0.33. The wind tunnel height (CH) was varied similarly, and data were recorded for H/CH = 1, 0.67, and 0.33 while the duct Reynolds number was varied between 2000 through 14000. An empirical bypass correlation has been fitted to the experimental data. Generally, the agreement between experimental data and correlation is within +/-10% for the thermal resistance, and within +/-20% for the pressure drop. From the experimental data, the fraction of the total airflow passing through the heat sink have been estimated and are compared to a simple physical bypass model.

  • 106.
    Jonsson, Hans
    et al.
    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.
    Thermal and Hydraulic Behavior of Plate Fin and Strip Fin Heat Sinks Under Varying Bypass Conditions1998In: 6th InterSociety Conf. on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm´98), 1998, p. 96-103Conference paper (Refereed)
  • 107.
    Kaern, Martin Ryhl
    et al.
    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..
    Meyer, Knud Erik
    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.
    Holst, Jörgen
    Danfoss Drives AS, Grasten, Denmark..
    Continuous versus pulsating flow boiling. Experimental comparison, visualization, and statistical analysis2017In: Science and Technology for the Built Environment, ISSN 2374-4731, E-ISSN 2374-474X, Vol. 23, no 6, p. 983-996Article in journal (Refereed)
    Abstract [en]

    This experimental study investigates an active method for flow boiling heat transfer enhancement by means of fluid flow pulsation. The hypothesis is that pulsations increase the flow boiling heat transfer by means of better bulk fluid mixing, increased wall wetting, and flow-regime destabilization. The fluid pulsations are introduced by a flow modulating expansion device and are compared with continuous flow by a stepper-motor expansion valve in terms of time-averaged heat transfer coefficient. The cycle time ranges from 1 to 9 s for the pulsations. The time-averaged heat transfer coefficients are reduced from transient measurements immediately downstream of the expansion valves at low vapor qualities. The results show that the pulsations improve the time-averaged heat transfer coefficient by 3.2% on average at low cycle time (1 to 2 s), whereas the pulsations may reduce the time-averaged heat transfer coefficient by as much as 8% at high heat flux (q >= 35 kW/m(2)) and cycle time (8 s). The latter reduction is attributed to a significant dry-out that occurs when the flow modulating expansion valve is closed. Additionally, the effect of fluid flow pulsations is found to be statistically significant, disregarding the lowest heat flux measurements.

  • 108.
    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.

  • 109.
    Kamal, Md.M
    et al.
    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.
    Property Model and Correlations for Calculation of Thermodynamic and Transport Properties of Carbon Dioxide in the Supercritical Region2005In: Proc. IIR Conf on Thermophysical Properties and Transfer Processes of Refrigerants, Vicenza, Italy, Aug./Sept. 2005., Vicenza, Italy: Academic Conferences Publishing, 2005Conference paper (Refereed)
  • 110.
    Kazachkov, Ivan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Analysis of Annular Two-phase Flow Dynamics under Heat Transfer Conditions2005In: Journal of Enhanced Heat Transfer, ISSN 1065-5131, E-ISSN 1563-5074, Vol. 1, p. 1-22Article in journal (Refereed)
    Abstract [en]

    An analytical investigation was performed for the instability phenomenon of two-phase annular flow with a thin film flow on the channel wall under the heat transfer conditions. The analyses of heat transfer behaviours of two-phase annular flow showed that the overall heat transfer behaviours between the fluids and the channel wall were dominated by the thickness of a thin liquid film. The mass, momentum and energy equations for two phases were employed to study the perturbation behaviours in both fluids. Two different boundary conditions at the wall were considered: heat transfer with constant temperature along the wall and then conditions of constant heat transfer along the wall. Basic equations were solved on both hydrodynamic and thermal perturbations in two fluids for two different boundary conditions. Scrupulous analysis was done for the axially symmetrical wave at two-phase interface. The results showed that in case of small flow rate, the hydrodynamic perturbations in both fluids always decreased. Only kinematical waves at the gas-liquid interface could exist, but did not grow. The waves moved at the same velocity as the gas phase in the channel core. However, the thermal perturbations might grow in some conditions. They finally caused hydrodynamic perturbations, which might also grow, causing a flow instability. The solutions for characteristics of the interface waves such as wavelength and increment of perturbations were obtained. More interestingly, for the isothermal boundary conditions it was found that the maximum increment of perturbations (most unstable) was only dependent on the thermodynamical property ratios of the gas and liquid.

  • 111. Khodabandeh, R.
    et al.
    Palm, Björn E.
    KTH, Superseded Departments, Energy Technology.
    Influence of system pressure on the boiling heat transfer coefficient in a closed two-phase thermosyphon loop2002In: International journal of thermal sciences, ISSN 1290-0729, E-ISSN 1778-4166, Vol. 41, no 7, p. 619-624Article in journal (Refereed)
    Abstract [en]

    In recent years heat generation from electronic components has been rapidly increasing. Natural and forced convection air-cooled heat sinks are not well suited for cooling the components generating the highest heat fluxes. Other methods are therefore sought. Recently the use of thermosyphons has attracted attention as a simple and effective cooling system for high heat flux components. In a thermosyphon system the heat is absorbed during boiling and transferred as heat of vaporization from the hot part to the cold part of the system, with relatively small temperature differences. The setup used in this study consists of a thermosyphon loop, including evaporator, condenser, downcomer and riser. The loop has three evaporators, connected in parallel, made from small blocks of copper (10 x 20 x 15) mm in which five vertical channels with diameters 1.5 mm and length 15 min were drilled. Experimental results in terms of heat transfer coefficients at different system pressures and heat inputs are presented and compared to predictions of correlations from the literature. In all tests Isobutane is used as working fluid.

  • 112.
    Khodabandeh, Rahmatollah
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Haglind, David
    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.
    Flow Pattern and Void Fraction in an Advanced Two-Phase Flow Thermosyphon Loop2006Conference paper (Refereed)
  • 113.
    Khodabandeh, Rahmatollah
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Jonsson, F.
    Han, X.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Spray Cooling of Electronic Components2007Conference paper (Refereed)
  • 114.
    Khodabandeh, Rahmatollah
    et al.
    KTH, Superseded Departments, Energy Technology.
    Palm, Björn E.
    KTH, Superseded Departments, Energy Technology.
    An experimental investigation of the influence of threaded surface on the boiling heat transfer coefficients in vertical narrow channels2002In: Microscale thermophysical engineering (Print), ISSN 1089-3954, E-ISSN 1091-7640, Vol. 6, no 2, p. 131-139Article in journal (Refereed)
    Abstract [en]

    One efficient method of cooling electronics is to use a closed-loop two-phase thermosyphon system. The setup tested here utilizes three small evaporators connected in parallel, each made from a small block of copper in which five vertical channels with diameter 1.5 mm and length 15 mm were drilled. The article presents the experimental results in terms of heat transfer coefficients of smooth surfaces as well as for threaded surfaces. Tests were done at different heat fluxes while maintaining constant system pressure. Tests were performed with heat loads of 30-450 W dissipated through the system. Two different refrigerants, R134a and R600a, were tested. The experimental two-phase flow heat transfer coefficients were compared to correlations from the literature.

  • 115.
    Khodabandeh, Rahmatollah
    et al.
    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.
    Kemper, Stephen
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mass Flow of an Advanced Two-Phase Thermosyphon Loop2005Conference paper (Other academic)
  • 116. Kobelt, R.
    et al.
    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.
    Oellrich, L.R.
    Heat transfer characteristics of nanofluids in two-phase flow boiling2009Conference paper (Other academic)
  • 117. Laanearu, J.
    et al.
    Borodinecs, A.
    Rimeika, M.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    A review on potential use of low-temperature water in the urban environment as a thermal-energy source2017In: 3RD INTERNATIONAL CONFERENCE ON INNOVATIVE MATERIALS, STRUCTURES AND TECHNOLOGIES (IMST 2017) / [ed] Rucevskis, S Bajare, D Erdmane, D Vitola, L, IOP PUBLISHING LTD , 2017, article id UNSP 012054Conference paper (Refereed)
    Abstract [en]

    The thermal-energy potential of urban water sources is largely unused to accomplish the up-to-date requirements of the buildings energy demands in the cities of Baltic Sea Region. A reason is that the natural and excess-heat water sources have a low temperature and heat that should be upgraded before usage. The demand for space cooling should increase in near future with thermal insulation of buildings. There are a number of options to recover heat also from wastewater. It is proposed that a network of heat extraction and insertion including the thermalenergy recovery schemes has potential to be broadly implemented in the region with seasonally alternating temperature. The mapping of local conditions is essential in finding the suitable regions (hot spots) for future application of a heat recovery schemes by combining information about demands with information about available sources. The low-temperature water in the urban environment is viewed as a potential thermal-energy source. To recover thermal energy efficiently, it is also essential to ensure that it is used locally, and adverse effects on environment and industrial processes are avoided. Some characteristics reflecting the energy usage are discussed in respect of possible improvements of energy efficiency.

  • 118.
    Li, Shanghua
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Furberg, Richard
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Nature-inspired boiling enhancement by novel nanostructured macroporous surfaces2008In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 18, no 15, p. 2215-2220Article in journal (Refereed)
    Abstract [en]

    World energy crisis has triggered more attention to energy saving and energy conversion systems. Enhanced surfaces for boiling are among the applications of great interest since they can improve the energy efficiency of heat pumping equipment (i.e., air conditioners, heat pumps, refrigeration machines). Methods that are used to make the state-of-the-art enhanced Surfaces are often based on complicated mechanical machine tools, are quite material-consuming and give limited enhancement of the boiling heat transfer. Here, we present a new approach to fabricate enhanced surfaces by using a simple electrodeposition method with in-situ grown dynamic gas bubble templates. As a result, a well-ordered 3D macro-porous metallic surface layer with nanostructured porosity is obtained. Since the structure is built based on the dynamic bubbles, it is perfect for the bubble generation applications Such as nucleate boiling. At heat flux of 1W cm(-2), the heat transfer coefficient is enhanced over 17 times compared to a plain reference Surface. It's estimated that such ail effective boiling surface Would improve the energy efficiency of many heat Pumping machines with 10-30%. The extraordinary boiling performance is explained based on the structure characteristics.

  • 119.
    Li, Shanghua
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Furberg, Richard
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Toprak, Muhammet
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zhang, Yu
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Fabrication of nanostructured micro-porous surfaces for enhanced boilingManuscript (Other academic)
  • 120.
    liu, qingming
    et al.
    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.
    Numerical study of bubbles rising and merging during convective boiling in micro-channels2016In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 99, p. 1141-1151Article in journal (Refereed)
    Abstract [en]

    A three dimensional numerical study on bubble growth and merger in a micro-channel with diameter of 0.64 mm has been conducted. The working fluid is R134a and the wall material is steel. The inlet Reynolds number is set at 549 in order to keep the flow in laminar regime. Two different heat fluxes () are supplied to the wall to heat up the fluid. The coupled level set and volume of fluid (CLSVOF) method is used to capture the distorted two-phase interface. An evaporation model is also implemented through UDF (User defined function). The combination of these two methods has successfully eliminated spurious velocities which is a common problem in two phase flow simulation. The boiling and merger processes are well-predicted by the simulation. It is found that the whole process can be divided into three sub-stages: sliding, merger, and post-merger. The dynamics and heat transfer are found to be different in these stages. The evaporation rate is much higher in the first two stages due to the thermal boundary layer effects.

  • 121.
    Liu, Qingming
    et al.
    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.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Simulation on the flow and heat transfer characteristics of confined bubbles in micro-channels2012In: ASME 2012 10th Int. Conf. on Nanochannels, Microchannels, and Minichannels Collocated with the ASME 2012 Heat Transfer Summer Conf. and the ASME 2012 Fluids Engineering Division Sum, ICNMM 2012, 2012, p. 63-70Conference paper (Refereed)
    Abstract [en]

    3D simulations on confined bubbles in micro-channels with diameter of 1.24 mm were conducted. The working fluid is R134a with a mass flux range from 125kg/m2s to 375kg/m2s. The VOF model is chosen to capture the 2 phase interface while the geo-construction method was used to re-construct the 2-phase interface. A heated boundary wall with heat flux varying from 15kW/m2 to 102kW/m2 is supplied. The wall temperature was calculated. The effects of mass flux and heat flux are studied. The shape of the bubble was predicted by the simulation successfully and the results show that they are independent of the initial shape. Both thin film evaporation and micro convection enhance the heat transfer. However, the micro convection which is caused by bubble motion has greater contribution to the total heat transfer at the stage of bubble growth studied.

  • 122.
    Liu, Qingming
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Wang, Wujun
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    A numerical study of the transition from slug to annular flow in micro-channel convective boiling2017In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 112, p. 73-81Article in journal (Refereed)
    Abstract [en]

    A numerical study on the transition from slug flow (or elongated flow) to annular flow of convective boiling under high heat flux in a micro-channel with diameter of 0.4 mm is conducted. A constant velocity inlet boundary with mass flux 400 kg/m2 s, and heated wall with a constant heat flux (160, 80 kW/m2) are applied. A novel initialization method is proposed. Growth rate of the bubble and transition of the flow regime are well predicted by comparing with an experimental visualization. Effects of the transition are studied and findings are that this process disturbs thermal boundary layer which further enhances bubble evaporation.

  • 123.
    Liu, Qingming
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Wang, Wujun
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Numerical study of the interactions and merge of multiple bubbles during convective boiling in micro channels2017In: International Communications in Heat and Mass Transfer, ISSN 0735-1933, E-ISSN 1879-0178, Vol. 81, p. 116-123Article in journal (Refereed)
    Abstract [en]

    Multi bubbles interaction and merger in a micro-channel flow boiling has been numerically studied. Effects of mass flux (56, 112, 200, and 335 kg/m2 ∗ s), wall heat flux (5, 10, and 15 kW/m2) and saturated temperature (300.15 and 303.15 K) are investigated. The coupled level set and volume of fluid (CLSVOF) method and non-equilibrium phase model are implemented to capture the two-phase interface, and the lateral merger process. It is found that the whole transition process can be divided to three sub-stages: sliding, merger, and post-merger. The evaporation rate is much higher in the first two stages due to the boundary layer effects in. Both the mass flux and heat flux affect bubble growth. Specifically, the bubble growth rate increase with the increase of heat flux, or the decrease of mass flux.

  • 124.
    Liu, Qingming
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Wang, Wujun
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Numerical study of the interactions and merge of multiple bubbles during convective boiling in micro channels2017In: International Communications in Heat and Mass Transfer, ISSN 0735-1933, E-ISSN 1879-0178, Vol. 80, p. 10-17Article in journal (Refereed)
    Abstract [en]

    Multi bubbles interaction and merger in a micro-channel flow boiling has been numerically studied. Effects of mass flux (56, 112, 200, and 335 kg/m2 ∗ s), wall heat flux (5, 10, and 15 kW/m2) and saturated temperature (300.15 and 303.15 K) are investigated. The coupled level set and volume of fluid (CLSVOF) method and non-equilibrium phase model are implemented to capture the two-phase interface, and the lateral merger process. It is found that the whole transition process can be divided to three sub-stages: sliding, merger, and post-merger. The evaporation rate is much higher in the first two stages due to the boundary layer effects in. Both the mass flux and heat flux affect bubble growth. Specifically, the bubble growth rate increase with the increase of heat flux, or the decrease of mass flux.

  • 125.
    Liu, Qingming
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Wang, Wujun
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Numerical study of the interactions and merge of multiple bubbles during convective boiling in micro channels (vol 81, pg 116, 2017)2017In: International Communications in Heat and Mass Transfer, ISSN 0735-1933, E-ISSN 1879-0178, Vol. 81, p. R1-R1Article in journal (Refereed)
  • 126.
    Liu, Qingming
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Wang, Wujun
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Wang, Changhong
    Jiang, Xiang
    On the dynamics and heat transfer of bubble train in micro-channel flow boiling2017In: International Communications in Heat and Mass Transfer, ISSN 0735-1933, E-ISSN 1879-0178, Vol. 87, p. 198-203Article in journal (Refereed)
    Abstract [en]

    The dynamics and heat transfer characteristics of flow boiling bubble train moving in a micro channel is studied numerically. The coupled level set and volume of fluid (CLSVOF) is utilized to track interface and a non-equilibrium phase change model is applied to calculate the interface temperature as well as heat flux jump. The working fluid is R134a and the wall material is aluminum. The fluid enters the channel with a constant mass flux (335 kg/m(2)*s), and the boundary wall is heated with constant heat flux (14 kW/m(2)). The growth of bubbles and the transition of flow regime are compared to an experimental visualization. Moreover, the bubble evaporation rate and wall heat transfer coefficient have been examined, respectively. Local heat transfer is significantly enhanced by evaporation occurring vicinity of interface of the bubbles. The local wall temperature is found to be dependent on the thickness of the liquid film between the bubble train and the wall.

  • 127.
    Mader, Gunda
    et al.
    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.
    Brian, Elmegaard
    DTU.
    Economic potential of cycle layout changes in residential R290 air-water heat pumps.Manuscript (preprint) (Other academic)
  • 128.
    Mader, Gunda
    et al.
    Danfoss A/S, Denmark .
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Elmegaard, Brian
    DTU.
    Maldistribution in air-water heat pump evaporators: Part 1: Effects on evaporator, heat pump and system level2015In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 50, p. 207-216Article in journal (Refereed)
    Abstract [en]

    This paper presents an approach to quantify the effect of evaporator maldistribution on operating costs of air-water heat pumps. In the proposed simulation model maldistribution is induced by two parameters describing refrigerant phase and air flow distribution. Annual operating costs are calculated based on heat pump performance at distinct operating conditions. Results show that percentage increase of operating costs is similar for the three considered climate zones, even though the effect of maldistribution on heat pump performance varies with operating conditions. Differences in terms of absolute cost increase for the climate zones arise mainly due to a varying number of operating hours. Absolute cost increase is considerable in the average and especially colder climate zone and can only partly be reduced by enlarging the evaporator.

  • 129.
    Mader, Gunda
    et al.
    Danfoss AS Refrigerat & Air Conditioning, Denmark.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Elmegaard, Brian
    DTU.
    Maldistribution in air-water heat pump evaporators. Part 2: Economic analysis of counteracting technologies2015In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 50, p. 217-226Article in journal (Refereed)
    Abstract [en]

    In this study a methodology is applied to quantify the effect of evaporator maldistribution on operating costs of air-water heat pumps. The approach is used to investigate the cost-effectiveness of two technologies enabling to counteract maldistribution: a flash gas bypass setup and the individual superheat control in parallel evaporator channels. In the total cost of ownership analysis, different scenarios for climatic conditions, severity of maldistribution, and economic framework are considered. Results show that the flash gas bypass system is cost-effective only in a few conditions, namely severe maldistribution, high electricity prices, and colder climate. Investment in the individual superheat control technology, however, can be quickly amortized in many scenarios. For the warmer climate zone with a small number of operating hours counteracting of maldistribution does not pay off under the used economic assumptions.

  • 130.
    Mader, Gunda
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration. Danfoss A/S, Denmark.
    Tiedemann, Thomas
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Concepts to increase the seasonal coefficient of performance of an air-water heat pump: Comparison of costs and benets2013Conference paper (Refereed)
  • 131.
    Maqbool, Mohammad H.
    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.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ali, Rashid
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Two phase heat transfer of ammonia in a mini/micro channel2010In: Proceedings of the 8th International Conference on Nanochannels, Microchannels and Minichannels, 2010, ASME Press, 2010, p. 1639-1647Conference paper (Refereed)
    Abstract [en]

    Experiments have been performed to investigate heat transfer in a circular vertical mini channel made of stainless steel (AISI 316) with internal diameter of 1.70 mm and a uniformly heated length of 245 mm using ammonia as working fluid. The experiments are conducted for a heat flux range of 15 to 350 kW/m(2) and mass flux range of 100 to 500 kg/m(2)s. The effects of heat flux, mass flux and vapour quality on the heat transfer coefficient are explored in detail. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Experimental results are compared to predictive methods available in the literature for boiling heat transfer. The correlations of Cooper et al. [1] and Shah [3] are in good agreement with our experimental data.

  • 132.
    Maqbool, Mohammad H.
    et al.
    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.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ali, Rashid
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Two-phase pressure drop of ammonia in a mini/micro-channel2010In: Proceedings of the  8th International Conference on Nanochannels, Microchannels and Minichannels, 2010, ASME Press, 2010, p. 1731-1739Conference paper (Refereed)
    Abstract [en]

    Experiments have been performed to investigate two-phase pressure drop in a circular vertical mini-channel made of stainless steel (AISI 316) with internal diameter of 1.70 mm and a uniformly heated length of 245 mm using ammonia as working fluid. The experiments are conducted for heat flux range of 15 to 350 kW/m(2) and mass flux range of 100 to 500 kg/m(2)s. A uniform heat flux is applied to the test section by DC power supply. Two phase frictional pressure drop variation with mass flux, vapour quality and heat flux was determined. The experimental results are compared to predictive methods available in literature for frictional pressure drop. The Homogeneous model and the correlation of Muller Steinhagen et al. [14] are in good agreement with our experimental data with MAD of 27% and 26% respectively.

  • 133.
    Maqbool, Muhammad Hamayun
    et al.
    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.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Boiling heat transfer of ammonia in vertical smooth mini channels: Experimental results and predictions2012In: International journal of thermal sciences, ISSN 1290-0729, E-ISSN 1778-4166, Vol. 54, p. 13-21Article in journal (Refereed)
    Abstract [en]

    In this article, flow boiling heat transfer results of ammonia in mini channels are reported. Experiments have been performed to investigate heat transfer in circular vertical mini channels made of stainless steel (AISI 316) with internal diameters of 1.70 mm and 1.224 mm and a uniformly heated length of 245 mm. The test conditions are: mass flux ranging from 100 to 500 kg/m2s, heat flux ranging from 15 to 355 kW/m2 and saturation temperatures of 23 °C, 33 °C and 43 °C. The effects of mass flux, heat flux, vapour quality, saturation temperature and internal diameter on heat transfer coefficients are explored in detail. The local heat transfer coefficients of ammonia with 1.70 mm tube at all vapour qualities and at lower vapour qualities with 1.224 mm tube, are more or less independent of mass flux and vapour quality and are a function of heat flux while the local heat transfer coefficients with 1.224 mm tube at higher vapour qualities are function of mass flux and vapour quality and independent of heat flux. The heat transfer coefficient is observed to be higher for lower internal diameter tube. The heat transfer coefficient is higher for higher saturation temperature at lower vapour qualities and no effect of saturation temperature is observed at higher vapour qualities for both test sections. The experimental data is compared with well known correlations and among them, the Cooper’s [1] correlation gave best predictions if all data points are included.

  • 134.
    Maqbool, Muhammad Hamayun
    et al.
    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.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Experimental investigation of dryout of propane in uniformly heated single vertical mini-channels2012In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 37, p. 121-129Article in journal (Refereed)
    Abstract [en]

    This article presents dryout results of propane in single vertical circular minichannels made of stainless steel with internal diameters of 1.70 mm and 1.224 mm. The heat flux is increased in steps up to occurrence of dryout. The effects of different parameters such as mass flux, saturation temperature, vapour quality and internal diameter on the dryout are investigated. The results show that the dryout heat flux increases with the increase in mass velocity, with the decrease of vapour quality and with the increase of internal diameter. Almost no effect of saturation temperature on dryout heat flux is observed. Generalised CHF correlations developed for macro and micro scale from the literature are also compared with the experimental results.

  • 135.
    Maqbool, Muhammad Hamayun
    et al.
    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.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow boiling of ammonia in vertical small diameter tubes: Two phase frictional pressure drop results and assessment of prediction methods2012In: International journal of thermal sciences, ISSN 1290-0729, E-ISSN 1778-4166, Vol. 54, p. 1-12Article in journal (Refereed)
    Abstract [en]

    Two phase pressure drops were measured for ammonia at a wide range of test conditions in two sizes of vertical mini channels. The test sections were made of stainless steel (AISI 316) tubes with internal diameter of 1.70 mm and 1.224 mm and a uniformly heated length of 245 mm. Experiments were conducted at three saturation temperatures of 23 °C, 33 °C and 43 °C, the heat flux ranging from 15 to 355 kW/m2 and the mass flux ranging from 100 to 500 kg/m2s. The effect of the heat flux, the mass flux, the vapour quality, the saturation temperature and the internal diameter on the two phase pressure drop are presented in this article. Some generalized two phase pressure drop correlations suggested for macro and micro scale channels are examined by comparing them with our experimental data. None of the examined correlations agreed well with the test data. A new correlation (modified form of Tran et al. correlation) is proposed which is able to predict the experimental data with MAD of 16% and 86% of the data is within ±30% range.

  • 136.
    Maqbool, Muhammad Hamayun
    et al.
    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.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Investigation of two phase heat transfer and pressure drop of propane in a vertical circular minichannel2013In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 46, p. 120-130Article in journal (Refereed)
    Abstract [en]

    This article reports the flow boiling heat transfer and pressure drop results of propane in a vertical circular stainless steel minichannel having an internal diameter of 1.70 mm and a heated length of 245 mm. Two phase heat transfer and pressure drop experiments have been performed at saturation temperatures of 23, 33 and 43 degrees C. Heat flux is varied from 5 to 280 kW/m(2) and mass flux is varied from 100 to 500 kg/m(2) s. The results show that the two phase frictional pressure drops, as expected, are increased with the increase of mass flux, vapour qualities and with the decrease of saturation temperature. The heat transfer coefficients are showed to increase with the increase of heat flux and saturation temperature while the influence of mass flux and vapour quality is observed as insignificant. After incipience of dryout, the decrease in heat transfer coefficient and also the two phase frictional pressure drop, especially at higher mass fluxes, is observed. The two phase frictional pressure drop correlations of Muller-Steinhagen and Heck and Friedel and two phase flow heat transfer correlations of Cooper and Liu and Winterton well predicted the experimental results.

  • 137.
    Maqbool, Muhammad Hamayun
    et al.
    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.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Parametric Effects on Dryout of Propane in a Vertical Circular Mini-Channel2011Conference paper (Refereed)
    Abstract [en]

    This article presents dryout results of propane in a vertical circular mini channel made of stainless steel with an internal diameter of 1.70 mm and a heated length of 245 mm. The experiments are performed at three saturation temperatures of 23 oC, 33 oC and 43 oC. Mass flux is varied from 100 kg/m2s to 500 kg/m2s.The heat flux is increased in steps up to occurrence of dryout. The effect of different parameters such as mass flux, vapour quality and saturation temperature on the dryout heat flux is investigated. The results show that the dryout heat flux increases with the increase in mass flux and with the decrease of vapour quality. Almost no effect of saturation temperature on the dryout heat flux is observed. The generalised CHF correlations developed for macro and micro scale from the literature are compared with experimental results. Correlations developed by Callizo et al. (2008), Bowring (1972) and Katto and Ohno (1984) gave reasonably good predictions.

  • 138.
    Maqbool, Muhammad Hamayun
    et al.
    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.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ali, Rashid
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Experimental Investigation of Two Phase Pressure Drop in a vertical mini-channel at three saturation pressures2010In: Proceedings of the 2nd European Conference on Microfluidics - Microfluidics 2010 - Toulouse, December 8-10, 2010, SHF , 2010Conference paper (Refereed)
    Abstract [en]

    Experiments are performed to study the behavior of  the two phase flow pressure drop of ammonia , in a vertical mini channel made of  stainless steel having an internal diameter of 1.224 mm and a heating length of 245 mm. The test conditions are: mass fluxes from 200 to 500 kg/m2s, heat fluxes from 20 to 340 kW/m2 and saturation temperatures of 23oC,33oC and 43oC. The experimental results are compared to well known correlations for frictional pressure drop in macro and micro scale channels.

  • 139.
    Maqbool, Muhammad Hamayun
    et al.
    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.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Rizwan Ali, Rahmat
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Saturated Flow boiling Heat Transfer Characteristics of Propane in a Smooth Vertical Minichannel up to Dryout Incipience2011In: 23rd IIR International Congress of Refrigeration, 2011, p. 2794-2801Conference paper (Refereed)
    Abstract [en]

    In this article the two phase heat transfer results of propane are presented. Experiments are performed up to dryout incipience in a circular mini channel made of stainless steel (AISI 316) having an internal diameter of 1.70 mm and a heated length of 245 mm. Experimental tests are done at a saturation temperature of 23 oC and for a heat flux range 5 - 240 kW/m2. Mass flux ranges from 100 to 400 kg/m2s. The effects of mass flux, heat flux and vapour quality on heat transfer coefficient are explored in detail. The results shows that the local heat transfer coefficients of propane are more or less independent of mass flux and vapour quality and is a strong function of heat flux until the occurrence of partial dryout. Finally the experimental results are compared with well known micro and macro scale correlations from the literature.

  • 140.
    Martin Callizo, Claudi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ali, Rashid
    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.
    New experimental results on flow boiling of R-134a in a vertical microchannel2007In: Proc. 10th UK Heat Transfer, Academic Conferences Publishing, 2007Conference paper (Refereed)
    Abstract [en]

    With the rapid development of micro electronic devices and micro manufacturing technology, heat transfer in microchannels has become increasingly important. However, the governing phenomena are not yet well understood.This paper presents new experimental results on flow boiling of R-134a in a vertical microchannel. Local heat transfer coefficients are measured along a single metal tube with internal diameter of 640 μm and a uniformly heated length of 213 mm, for three different mass fluxes, 250, 400 and 600 kg/m2s, two system pressures, 7.70 and 8.87 bar at the inlet (corresponding to saturation temperatures of 30 and 35 ºC), heat fluxes ranging from 5 to 70 kW/m2, and vapour qualities up to 0.89.From the experimental results it is clear that the heat transfer coefficient increases with heat flux and system pressure and does not change with vapour quality or mass flux when the quality is less than 0.45–0.50. For higher vapour qualities, the heat transfer coefficient decreases with vapour quality and the effect of the heat flux on the heat transfer coefficient seems to diminish. This deterioration of the heat transfer coefficient is believed to be caused by the occurrence of intermittent dry out in this vapour quality range.The experimental heat transfer coefficients are compared against predictions from three generalized models, two developed specifically for microscale geometries and one for conventional channels, showing unsatisfactory agreement, especially for the high vapour quality range.

  • 141.
    Martin Callizo, Claudi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Owhaib, WahibKTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.Palm, BjörnKTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Subcooled Flow Boiling Heat Transfer and Visualization of R-134a in a Vertical Transparent Heated Tube of Small Diameter2005Conference proceedings (editor) (Refereed)
  • 142.
    Martin Callizo, Claudi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Owhaib, WahibKTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.Palm, BjörnKTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Subcooled Flow Boiling of R134a in a Vertical Channel of Small Diameter2005Conference proceedings (editor) (Refereed)
  • 143.
    Martin-Callizo, Claudi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ali, Rashid
    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 incipience and critical heat flux in saturated flow boiling of refrigerants in a vertical uniformly heated microchannel2008In: PROCEEDINGS OF THE 6TH INTERNATIONAL CONFERENCE ON NANOCHANNELS, MICROCHANNELS, AND MINICHANNELS, PTS A AND B, NEW YORK: AMER SOC MECHANICAL ENGINEERS , 2008, p. 705-712Conference paper (Refereed)
    Abstract [en]

    The prediction of dryout occurrence is crucial in the design and safety of compact heat exchangers. For this purpose, a series of experimental tests have been performed to investigate dryout incipience and critical heat flux (CHF) in a circular vertical microchannel with internal diameter of 640 mu m and a uniformly heated length of 213 mm using refrigerants R-134a, R-22 and R-245fa as working fluids. The effects of mass flux, system pressure, and refrigerant on the dryout heat flux and vapour quality are explored in detail. Finally, the experimental CHF results are compared to existing correlations both specially developed for microchannels and for macroscale geometries. The comparison shows good agreement with the classical Katto and Ohno (1984) correlation, developed for conventional large tubes. On the other hand, none of the microchannel correlations predicts in agreement the experimental data.

  • 144. Martin-Callizo, Claudi
    et al.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Owhaib, Wahib
    Subcooled flow boiling of R-134a in vertical channels of small diameter2007In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 33, no 8, p. 822-832Article in journal (Refereed)
    Abstract [en]

    Subcooled flow boiling heat transfer for refrigerant R- 134a in vertical cylindrical tubes with 0.83, 1.22 and 1.70 turn internal diameter was experimentally investigated. The effects of the heat flux, q = 1-26 kW/m 2, mass flux, G = 300-700 kg /m(2) s, inlet subcooling, Delta T-sub,T-i = 5-15 degrees C, system pressure, P = 7.70-10.17 bar, and channel diameter, D, on the subcooled boiling heat transfer were explored in detail. The results are presented in the form of boiling curves and heat transfer coefficients. The boiling curves evidenced the existence of hysteresis when increasing the heat flux until the onset of nucleate boiling, ONB. The wall superheat at ONB was found to be essentially higher than that predicted with correlations for larger tubes. An increase of the mass flux leads, for early subcooled boiling, to an increase in the heat transfer coefficient. However, for fully developed subcooled boiling, increases of the mass flux only result in a slight improvement of the heat transfer. Higher inlet subcooling, higher system pressure and smaller channel diameter lead to better boiling heat transfer. Experimental heat transfer coefficients are compared to predictions from classical correlations available in the literature. None of them predicts the experimental data for all tested conditions.

  • 145.
    Martin-Callizo, Claudi
    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.
    Owhaib, Wahib
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ali, Rashid
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow Boiling Visualization of R-134a in a Vertical Channel of Small Diameter2010In: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 132, no 3, p. 031001-Article in journal (Refereed)
    Abstract [en]

    The present work reports on flow boiling visualization of refrigerant R-134a in a vertical circular channel with an internal diameter of 1.33 mm and 235 mm in heated length. A quartz tube with a homogeneous Indium Tin Oxide coating is used to allow heating and simultaneous visualization. Flow patterns have been observed along the heated length with the aid of high-speed complementary metal oxide semiconductor (CMOS) digital camera. From the flow boiling visualization, seven distinct two-phase flow patterns have been observed: isolated bubbly flow, confined bubbly flow, slug flow, churn flow, slug-annular flow, annular flow, and mist flow. Two-phase flow pattern observations are presented in the form of flow pattern maps. The effects of the saturation temperature and the inlet subcooling degree on the two-phase flow pattern transitions are elucidated. Finally, the experimental flow pattern map is compared with models developed for conventional sizes as well as to a microscale map for air-water mixtures available in literature, showing a large discrepancy.

  • 146.
    Martin-Callizo, Claudi
    et al.
    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.
    Owhaib, Wahib
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ali, Rashid
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Flow boiling visualization of R-134a in a vertical channel of small diameter2007In: 2007 Proceedings of the ASME/JSME Thermal Engineering Summer Heat Transfer Conference - HT 2007 Volume 1, 2007, p. 135-143Conference paper (Refereed)
    Abstract [en]

    The present work reports on flow boiling visualization of refrigerant R-134a in a vertical circular channel with internal diameter of 1.33 mm and 23 5 mm in heated length. Quartz tube with a homogeneous ITO-coating is used allowing heating and simultaneous visualization. Flow patterns have been observed along the heated length with the aid of a digital camera with close-up lenses. From the flow boiling visualization, seven distinct two-phase flow patterns have been observed: Isolated bubbly flow, confined bubbly flow, slug flow, churn flow, slug-annular flow, annular flow, and mist flow. Two-phase flow pattern observations are presented in the form of flow pattern maps. Finally, the experimental flow pattern map is compared to models developed for conventional sizes as well as to a microscale map for air-water mixtures available in the literature, showing a large discrepancy.

  • 147.
    Martín-Callizo, Claudi
    et al.
    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.
    Owhaib, Wahib
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Investigation on Nucleate Boiling Incipience in Subcooled Flow of Refrigerant R-134a through Narrow Channels2006Conference paper (Other academic)
  • 148. Martínez-Galván, Eduardo
    et al.
    Ramos, Juan Carlos
    Antón., Raul
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Heat transfer and film thickness measurements in a closed loop spray cooling system with R134a2009In: 15th International Workshop on Thermal Investigations of ICs and Systems, THERMINIC 2009, Academic Conferences Publishing, 2009, p. 180-185Conference paper (Refereed)
    Abstract [en]

    Experimental measurements in a spray cooling test rig have been carried out for different heat fluxes in the heater and different volumetric spray fluxes of the refrigerant. Results of the thermal parameters and the sprayed refrigerant liquid film thickness over the heater are presented. The film thickness measurements have been made with a high speed camera equipped with a long distance microscope. It has been found that there is a relation between the variation of the heat transfer coefficient and the film thickness along the spray boiling curve.

  • 149.
    Mazzotti, Willem
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Lazzarotto, Alberto
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Deep Boreholes for Ground-Source Heat Pump: Final report2018Report (Refereed)
    Abstract [en]

    This report presents the obtained results and performed tasks during the project Deep Boreholes for Ground-Source Heat Pumps, within the framework of the research program Effsys Expand.

    A price model for the investment of GSHP system with deep Borehole Heat Exchangers (BHEs) is derived from a survey submitted to Swedish drillers. Notably, it is shown that the price increases with the borehole depth in a cubic fashion. Up to 300 m depth, the model shows a good match with a linear correlation having a slope of 275 SEK/m, a figure that is close to commonly used estimates for the total installation price of a single BHE. For larger depths, however, the installation price becomes non-linear and deviates from this linear tendency. Examples of total installation prices, including heat pumps and BHEs installation, are given.

    Measurements performed in three different installations with deep boreholes are reported. The first tests are performed in a 800 m deep borehole equipped with acoaxial collector. Five Distributed Thermal Response Tests (DTRTs) are performed inthis BHE of which four were heat-extraction DTRTs. It is shown that heat flux inversion happens along the depth of the boreholes, that is heat is extracted at the bottom of the borehole but lost at the top. The flow rate is shown to have a significant effect on the thermal shunt effect and the coaxial BHE is shown to have significantly lower pressure drops that more traditional BHE (e.g. U-pipes). The pressure drop vs. flow rate relation is experimentally characterized through a hydraulic step test. An effective borehole resistance of 0.21 m∙K/W was found. This value is relatively high and is explained as a consequence of limited flow rate and the large depth. More investigations as regards the measurement technique (DTS with fiber optic cables) are needed before performing further in-depth analysis.

    In another installation, four 510 m boreholes are measured to deviate about 30% from the vertical direction, highlighting the importance of drilling precision for deep boreholes, more particularly in urban environment. The GSHP system, using 50mmU-pipe BHEs is monitored over a year and it is found that pumping energy consumption in the boreholes could be as high as 22% of the total energy consumption of the system (compressors and circulation pumps). The relevance of pressure drops and control strategies for the circulation pumps in the borehole loop is emphasized. The temperature profile with depth confirms the existence of stored heat in the top part of the ground in urban environment.

    The results of two DTRTs performed in the same borehole (335 m) are reported, thelatter being first water-filled before being grouted. The obtained thermal conductivities differ from one case to another, possibly highlighting the effect of the filling material on the results. Several other explanations are proposed although none can be fully verified.

    The design and construction phases of a laboratory-scale borehole storage model are reported. The design phase mainly focused on deriving analytical scaling laws and finding a suitable size for such a model. Through the design analysis, an explanation to the discrepancy observed in the only previous attempt to validate long-term thermal behavior of boreholes is proposed.

    Investigations as regards the KTH heat pump system, optimum flow rates in GSHPsystems with deep BHEs and quantification of thermal influence between neighboringboreholes are discussed although the work could not be fully completed within thetimeframe of the project.

    The dissemination of knowledge through different activity is reported.

  • 150.
    Mazzotti, Willem
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration. Bengt Dahlgren AB.
    Firmansyah, Husni
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Acuña, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration. Bengt Dahlgren AB.
    Stokuca, Milan
    Bengt Dahlgren AB.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    The Newton-Raphson MethodApplied to the Time-Superposed ILS for Parameter Estimation in Thermal Response Tests2018In: Research Conference Proceedings: International Ground-Source Heat Pump Association Research Conference 2018 / [ed] Jeffrey Spitler, José Acuña, Michel Bernier, Zhaohong Fang, Signhild Gehlin, Saqib Javed, Björn Palm, Simon J. Rees, 2018, p. 208-218Conference paper (Refereed)
    Abstract [en]

    Thermal Response Testing is now a well-known and widely-used method allowing the determination of the local thermal or geometrical properties of aBorehole Heat Exchanger (BHE), those properties being critical in the design of GSHP systems. The analysis of TRTs is an inverse problem that hascommonly been solved using an approximation of the ILS solution. To do this, however, the heat rate during a TRT must be kept constant, or least be nontime-correlated, during the test, which is a challenging constraint. Applying temporal superposition to the ILS model is a way to account for varying power,although it requires the use of an optimization algorithm to minimize the error between a parametrized model and experimental values.In this paper, the Newton-Raphson method is applied to the time-superposed ILS for parameter estimation in TRTs. The parameter estimation is limitedto the effective thermal conductivity and the effective borehole resistance. Analytical expressions of the first and second derivatives of the objective function,chosen as the sum of quadratic differences, are proposed, allowing to readily inverse of the Hessian matrix and speed the convergence process.The method is tried for 9 different TRTs, 2 of which are reference datasets used for validation of the method (Beier et al., 2010). Differences betweenestimated and reference thermal conductivities are of 3.4% and 0.4% for the first and second reference TRTs, respectively. The method is shown to be stableand consistent: for each of the 9 TRTs, 11 realizations are performed with different initial values. Convergence is reached in all cases and all realizationslead to the same final values for a given TRT.The proposed convergence method is about 70% to 90% faster than the Nelder-Mead simplex and require about 8 times less iterations in average. Theconvergence speed varies between 0.3 to 13.6 s with an average of 3.7 s for all TRTs.

12345 101 - 150 of 216
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf