The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Ned Djilali - One of the best experts on this subject based on the ideXlab platform.
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analytic determination of the Effective Thermal Conductivity of pem fuel cell gas diffusion layers
Journal of Power Sources, 2008Co-Authors: Ehsan Sadeghi, Majid Bahrami, Ned DjilaliAbstract:Accurate information on the temperature field and associated heat transfer rates are particularly important in devising appropriate heat and water management strategies in proton exchange membrane (PEM) fuel cells. An important parameter in fuel cell performance analysis is the Effective Thermal Conductivity of the gas diffusion layer (GDL). Estimation of the Effective Thermal Conductivity is complicated because of the random nature of the GDL micro structure. In the present study, a compact analytical model for evaluating the Effective Thermal Conductivity of fibrous GDLs is developed. The model accounts for conduction in both the solid fibrous matrix and in the gas phase; the spreading resistance associated with the contact area between overlapping fibers; gas rarefaction effects in microgaps; and salient geometric and mechanical features including fiber orientation and compressive forces due to cell/stack clamping. The model predictions are in good agreement with existing experimental data over a wide range of porosities. Parametric studies are performed using the proposed model to investigate the effect of bipolar plate pressure, aspect ratio, fiber diameter, fiber angle, and operating temperature.
Lin Shi - One of the best experts on this subject based on the ideXlab platform.
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effect of temperature on the Effective Thermal Conductivity of n tetradecane based nanofluids containing copper nanoparticles
Particuology, 2015Co-Authors: Haifeng Jiang, Chao Huang, Lin ShiAbstract:Abstract Nanofluids were prepared by dispersing Cu nanoparticles (∼20 nm) in n-tetradecane by a two-step method. The Effective Thermal Conductivity was measured for various nanoparticle volume fractions (0.0001–0.02) and temperatures (306.22–452.66 K). The experimental data compares well with the Jang and Choi model. The Thermal Conductivity enhancement was lower above 391.06 K than for that between 306.22 and 360.77 K. The interfacial Thermal resistance increased with increasing temperature. The Effective Thermal Conductivity enhancement was greater than that obtained with a more viscous fluid as the base media at 452.66 K because of nanoconvection induced by nanoparticle Brownian motion at high temperature.
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Effective Thermal Conductivity of carbon nanotube-based nanofluid
Journal of the Taiwan Institute of Chemical Engineers, 2015Co-Authors: Haifeng Jiang, Qiang Zhang, Lin ShiAbstract:The Effective Thermal Conductivity of CNT/water nanofluid is measured with different CNT loadings (0.22-1 vol%) and temperatures (30-90 °C). The enhanced Thermal Conductivity increased nonlinearly with CNT concentrations while the ratios are almost constant with the rise of temperature. An aggregate-based model is proposed to predict the enhanced Thermal Conductivity of CNT-based nanofluid. The present model gives the lower and upper limits of CNT-based nanofluid with majority of the previous data fall within these bounds. CNT contact results in low-resistance heat conduction path which serves high Thermal Conductivity of nanofluid. The proposed model exhibits quite well an agreement with the experimental data and affords improved predictions for the enhanced Thermal Conductivity. The present study sheds light on the Thermal Conductivity mechanisms in CNT-based nanofluids with respect to CNT aggregate state in base fluids.
Runzhang Yuan - One of the best experts on this subject based on the ideXlab platform.
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fractal model for prediction of Effective Thermal Conductivity of gas diffusion layer in proton exchange membrane fuel cell
Journal of Power Sources, 2008Co-Authors: Ying Shi, Shuhai Quan, Jinsheng Xiao, Mu Pan, Runzhang YuanAbstract:Abstract The process of heat transfer within porous media is usually considered as a transport through large numbers of straight channels with uniform pore sizes. For the prediction of Effective Thermal Conductivity of gas diffusion layer (GDL), morphological properties such as the tortuosity of channels and pore-size distribution of this porous layer should be considered. Thus in this article, novel parallel and series-parallel prediction models of Effective Thermal Conductivity for the GDL in proton exchange membrane fuel cell (PEMFC) have been derived by fractal theoretical characterization of the real microstructure of GDL. The prediction of fractal parallel model for carbon paper, a basal material of the GDL, is in good agreement with the reference value supplied by Toray Inc. The prediction results from the proposed models are also reasonable because they are distributed between the upper and lower bounds. Parametric effect has been investigated by using the presented models in dimensionless formalism. It can be concluded that dimensionless Effective Thermal Conductivity ( k ′ eff ) has a positive correlation with Effective porosity (ɛ) or the pore-area fractal dimension (Dp) when ks/kg 1 and with tortuous fractal dimension (Dt) whether ks/kg
Xiulan Huai - One of the best experts on this subject based on the ideXlab platform.
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cfd study on Thermal transport in open cell metal foams with and without a washcoat Effective Thermal Conductivity and gas solid interfacial heat transfer
Chemical Engineering Science, 2017Co-Authors: Wenping Peng, Xiulan Huai, Zhigang Liu, Hua Sheng WangAbstract:Abstract Metal foams are considered to be attractive catalyst carriers for strongly exothermic/endothermic catalytic processes, but the washcoat may have a significant influence on the Thermal transport properties of the metal foams. In this work, the Effective Thermal Conductivity and the gas-solid interfacial heat transfer of coated metal foams were studied using a periodic unit cell model in the CFD method. We emphasized analysing the effect of the washcoat on the Effective Thermal Conductivity, pressure drop and interfacial heat transfer of metal foams. The results indicated that the influence of the washcoat on the Effective Thermal Conductivity depends on the Conductivity in three phases. A large deviation was found when we used the available empirical correlations for metal foams to predict the Effective Thermal Conductivity of the coated metal foams. A correlation for the Effective Thermal Conductivity of coated metal foams was proposed by considering the washcoat as a separate phase. With increasing washcoat thickness, it was found that the pressure drop increases but the gas-solid interfacial heat transfer decreases. Moreover, we verified the enhancement of viscous flow within the washcoat for coated metal foams. It was revealed that a maximum increase of the Nusselt number by a factor of approximately 13 was obtainable in turbulent flow if the viscous flow within the washcoat was accounted for. The present study may provide a guide for structured catalyst and reactor design for strongly exothermic/endothermic catalytic processes.
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analysis of the Effective Thermal Conductivity of fractal porous media
Applied Thermal Engineering, 2007Co-Authors: Xiulan Huai, Weiwei Wang, Zhigang LiAbstract:Abstract Several types of fractals are generated to model the structures of porous media, and heat conduction in these structures is simulated by the finite volume method (FVM). The influences of the Thermal Conductivity of solid k s , the Thermal Conductivity of fluid k f , the porosity e , the size and spatial distribution of pores on the Effective Thermal Conductivity k e of these structures are analysed in detail. The calculated results indicate that the relation of Effective Thermal Conductivity k e with Thermal Conductivity of solid k s and Thermal Conductivity of fluid k f conforms to a power function, and the relation of Effective Thermal Conductivity k e with porosity e conforms to an exponential function. The porosity e is the most important factor that determines the Effective Thermal Conductivity of fractal porous media, but the size and spatial distribution of pores, especially the spatial distribution of the bigger pores, do have substantive influence. The numerical results are analysed by comparing with the available empirical formulas from literatures, and provide verification of these empirical formulas.
Xianguo Li - One of the best experts on this subject based on the ideXlab platform.
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estimating Effective Thermal Conductivity in carbon paper diffusion media
Chemical Engineering Science, 2010Co-Authors: Nada Zamel, Xianguo Li, Jun Shen, Jurgen Becker, Andreas WiegmannAbstract:Heat management is crucial to polymer electrolyte membrane (PEM) fuel cell commercialization. Numerical modeling is often used to simulate heat transfer in the various components of the cell and specifically the gas diffusion layer (GDL). Due to the porous nature of the gas diffusion layer and its complexity of anisotropy, the effect of the structure on the Thermal Conductivity is usually taken into account by introducing an Effective Thermal Conductivity. In this study, the Effective Thermal Conductivity of carbon paper diffusion media was estimated numerically. Carbon paper is often used as the GDL in PEM fuel cells due to its ability to efficiently transport electrons, heat and gaseous species. Using the GeoDict code, a realistic three-dimensional pore morphology of carbon paper was used as the modeling domain and the governing mathematical equations were solved using the commercial software package Fluent (6.3.26) and the ThermoDict solver. The geometrical effects on the Effective Thermal Conductivity were investigated for different geometries. It was found that the Effective Thermal Conductivity is highly sensitive to the geometry of the porous material under investigation. The Effective Thermal Conductivity is much larger in the in-plane direction when compared with the value in the through-plane direction. Further, the change of the Effective Thermal Conductivity due to porosity and compression was studied. Finally, correlations for the through-plane and in-plane Effective Thermal Conductivity were developed.
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measurement of through plane Effective Thermal Conductivity and contact resistance in pem fuel cell diffusion media
Electrochimica Acta, 2010Co-Authors: Gholamreza Karimi, Xianguo Li, P. TeertstraAbstract:An experimental study was performed to determine the through-plane Thermal Conductivity of various gas diffusion layer materials and Thermal contact resistance between the gas diffusion layer (GDL) materials and an electrolytic iron surface as a function of compression load and PTFE content at 70 °°C. The Effective Thermal Conductivity of commercially available SpectraCarb untreated GDL was found to vary from 0.26 to 0.7 W/(m °°C) as the compression load was increased from 0.7 to 13.8 bar. The contact resistance was reduced from 2.4×10−42.4×10−4 m2°C/W at 0.7 bar to 0.6×10−40.6×10−4 m2°C/W at 13.8 bar. The PTFE coating seemed to enhance the Effective Thermal Conductivity at low compression loads and degrade Effective Thermal Conductivity at higher compression loads. The presence of microporous layer and PTFE on SolviCore diffusion material reduced the Effective Thermal Conductivity and increased Thermal contact resistance as compared with the pure carbon fibers. The Effective Thermal Conductivity was measured to be 0.25 W/(m °°C) and 0.52 W/(m °°C) at 70 °°C, respectively at 0.7 and 13.8 bar for 30%-coated SolviCore GDL with microporous layer. The corresponding Thermal contact resistance reduced from 3.6×10−43.6×10−4 m2°C/W at 0.7 bar to 0.9×10−40.9×10−4 m2°C/W at 13.8 bar. All GDL materials studied showed non-linear deformation under compression loads. The Thermal properties characterized should be useful to help modelers accurately predict the temperature distribution in a fuel cell.
