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  • 1.
    Ali, Rashid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Palm, Björn E.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Maqbool, Mohammad H.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Flow Boiling Heat Transfer Characteristics of a Minichannel up to Dryout Condition2011Ingår i: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 133, nr 8, s. 081501-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.70 mm and a uniformly heated length of 220 mm. R134a was used as a working fluid, and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 degrees C and 32 degrees C. Mass flux was varied from 50 kg/m(2) s to 600 kg/m(2) s, and heat flux ranged from 2 kW/m(2) to 156 kW/m(2). The test section was heated directly using a dc power supply. The direct heating of the channel ensured uniform heating, which was continued until dryout was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux, while mass flux and vapor quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that the dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.

  • 2.
    Ali, Rashid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Palm, Björn
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Martin-Callizo, C.
    Maqbool, Muhammad Hamayun
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Study of flow boiling characteristics of a microchannel using high speed visualization2013Ingår i: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 135, nr 8, s. 081501-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents the visualization results obtained for an experimental study of R134a during flow boiling in a horizontal microchannel. The microchannel used was a fused silica tube having an internal diameter of 781 lm, a heated length of 191mm, and was coated with a thin, transparent, and electrically conductive layer of indium-tin-oxide (ITO) on the outer surface. The operating parameters during the experiments were: mass flux 100-400 kg/m2 s, heat flux 5-45 kW/m2, saturation temperatures 25 and 30 °C, corresponding to saturation pressures of 6.65 bar and 7.70 bar and reduced pressures of 0.163 and 0.189, respectively. A high speed camera with a close up lens was used to capture the flow patterns that evolved along the channel. Flow pattern maps are presented in terms of the superficial gas and liquid velocity and in terms of the Reynolds number and vapor quality plots. The results are compared with some flow pattern maps for conventional and micro scale channels available in the literature. Rigorous boiling and increased coalescence rates were observed with an increase in the heat flux.

  • 3.
    Do-Quang, Minh
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.
    Pettersson, Claes-Ove
    Modeling of the adsorption kinetics and the convection of surfactants in a weld pool2008Ingår i: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 130, nr 9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents a comprehensive three-dimensional, time-dependent model for simulating the adsorption kinetics and the redistribution of surfactants at the surface and in the bulk of a weld pool. A physicochemical approach that was included in this paper allows the surfactant concentration at the surface and in the bulk to depart from its thermodynamical equilibrium. The Langmuir equilibrium adsorption ratio was based on the k(seg) coefficient of Sahoo (1988, "Surface-Tension of Binary Metal-Surface-Active Solute Systems Under Conditions Relevant to Welding Metallurgy," Metall. Trans. B, 19B, pp. 483-491) and was finally used for calculating fluid flow and heat transfer in gas tungsten arc welding of a super duplex stainless steel, SAF 2507. In this study, the authors applied the multicomponent surfactant mass transfer model to investigate the effect of the influence of sulfur and oxygen redistribution in welding of a super duplex stainless steel.

  • 4.
    Furberg, Richard
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Palm, Björn E.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Li, Shanghua
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Funktionella material, FNM.
    Toprak, Muhammet S.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Funktionella material, FNM.
    Muhammed, Mamoun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Funktionella material, FNM.
    The Use of a Nano- and Microporous Surface Layer to Enhance Boiling in a Plate Heat Exchanger2009Ingår i: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 131, nr 10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Presented research is an experimental study of the performance of a standard plate heat exchanger evaporator, both with and without a novel nano- and microporous copper structure, used to enhance the boiling heat transfer mechanism in the refrigerant channel. Various distance frames in the refrigerant channel were also employed to study the influence of the refrigerant mass flux on two-phase flow heat transfer. The tests were conducted at heat fluxes ranging between 4.5 kW/m(2) and 17 kW/m(2) with 134a as refrigerant. Pool boiling tests of the enhancement structure, under similar conditions and at various surface inclination angles, were also performed for reasons of comparison. The plate heat exchanger with the enhancement structure displayed up to ten times enhanced heat transfer coefficient in the refrigerant channel, resulting in an improvement in the overall heat transfer coefficient with over 100%. This significant boiling enhancement is in agreement with previous pool boiling experiments and confirms that the enhancement structure may be used to enhance the performance of plate heat exchangers. A simple superposition model was used to evaluate the results, and it was found that, primarily, the convective boiling mechanism was affected by the distance frames in the standard heat exchanger. On the other hand, with the enhanced boiling structure, variations in hydraulic diameter in the refrigerant channel caused a significant change in the nucleate boiling mechanism, which accounted for the largest effect on the heat transfer performance.

  • 5.
    Gubaidullin, Askar
    et al.
    KTH, Tidigare Institutioner, Fysik.
    Sehgal, Balraj
    KTH, Tidigare Institutioner, Fysik.
    Numerical analysis of natural convection and mixing in two-fluid stratified pools with internal heat sources2004Ingår i: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 126, nr 4, s. 600-610Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The heat transport in two-layer fluid systems has been investigated numerically for slice-type semicircular pools with internal heat sources. The fixed interface model has been applied to study natural convection in the system of the immiscible fluids. The double-diffusion model has been employed to describe the heat transfer and mixing for the miscible fluids. The numerical results are compared to data measured in the SIMECO experiments. Based on the numerical simulations, the effect of the ratio of the fluid properties has been quantified. The results are of interest for the corium melt coolability in a postulated severe accident scenario in a light water reactor.

  • 6. Hantsch, A.
    et al.
    Gross, U.
    Martin, Andrew R.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Heat Transfer Augmentation: Radiative-Convective Heat Transfer in a Tube With Fiber Array Inserts2010Ingår i: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 132, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Gas-phase heat transfer plays a critical role in many high temperature applications, such as preheaters, combustors, and other thermal equipment. In such cases common heat transfer augmentation methods rely on the convective component alone to achieve improved internal performance. Radiatively assisted heat transfer augmentation has been suggested as a way to overcome limitations in convective-only enhancement. One example of such a technique is the fiber array insert; thermal radiation emitted by tube walls is captured by a large number of slender fibers, which in turn convect heat to the flowing fluid. Previous numerical studies have indicated that this technique represents a promising enhancement method warranting further investigation. This paper presents results from an experimentally based feasibility study of fiber array inserts for heat transfer augmentation in an externally heated duct. Fibers composed of 140 mu m silicon carbide and 150 mu m stainless steel were assembled in arrays with porosities around 0.98, and were tested for empty-tube Reynolds numbers ranging from 17,500 to 112,500 and wall temperatures from ambient up to 750 degrees C. The arrays cause a significant pressure drop-roughly two orders of magnitude higher than the empty-tube case-but tube-side heat transfer coefficients were improved by up to 100% over the convective-only case in the low flow rate regime. The stainless steel fiber array exhibited similar heat transfer performance as the silicon carbide case, although pressure drop characteristics differed owing to variations in fluid-structure flow phenomena. Pressure drop data were roughly within the range of d'Arcy law predictions for both arrays, and deviations could be explained by inhomogeneities in fiber-to-fiber spacing. Heat transfer was found to depend nonlinearly on wall temperature and flow rate, in contrast to previously reported numerical data.

  • 7.
    Kutcherov, Vladimir
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.), Hållbarhet och industriell dynamik. Gubkin Russian State Univ Oil & Gas, Russia.
    Chernoutsan, Alexey
    Kolesnikov, Anton
    Grigoriev, Boris
    Thermal Conductivity of Complex Hydrocarbon Systems at Pressures Up To 1000 MPa2016Ingår i: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 138, nr 11, artikel-id 112003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The thermal conductivity of five samples of crude oil and one sample of gas condensate was measured by the transient hot-wire technique. The measurements were made along isotherms ( 245, 250, 273, 295, 320, 336, and 373 K) in the pressure range from atmospheric pressure up to 1000 MPa and along isobars ( at 0.1, 100, 200, 300, 400, 500, and 1000 MPa) in the temperature range 245-450 K. It was observed that the thermal conductivity of the samples investigated strongly depends on the pressure and rises with increasing pressure for all the temperatures. At a certain pressure, the temperature coefficient of thermal conductivity reverses from negative to positive. The pressure at which this reversal was observed varied in the range of 300-380 MPa.

  • 8.
    Martin-Callizo, Claudi
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Palm, Björn E.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Owhaib, Wahib
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Ali, Rashid
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Flow Boiling Visualization of R-134a in a Vertical Channel of Small Diameter2010Ingår i: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 132, nr 3, s. 031001-Artikel i tidskrift (Refereegranskat)
    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.

  • 9. Sinha, R.
    et al.
    Nayak, A. K.
    Sehgal, Bal Raj
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnkraftsäkerhet.
    Modeling the natural convection heat transfer and dryout heat flux in a porous debris bed2008Ingår i: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 130, nr 10, s. 104503-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An empirical model for natural convection heat transfer for film-boiling condition has been developed for volumetrically heated particulate debris beds when flooded with water at the top of the bed. The model has been derived from the quenching data generated in the POMECO facility located at KTH, Stockholm. A dry-out model is also developed for countercurrent flooding limiting condition when the heat generating saturated debris bed is flooded with water from the top. The model is in good agreement with the experimental data over a wide range of particle size and Porosity as compared to the existing models. The implication of the models with respect to quenching of porous debris bed formed during postulated severe accident condition is discussed.

  • 10.
    Wiberg, Roland
    et al.
    KTH, Tidigare Institutioner, Mekanik.
    Lior, N
    Temperature measurements using thermochromic liquid crystals2004Ingår i: Journal of heat transfer, ISSN 0022-1481, E-ISSN 1528-8943, Vol. 126, nr 4, s. 503-503Artikel i tidskrift (Refereegranskat)
1 - 10 av 10
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