Evaluation of models of the effective thermal conductivity of porous materials relevant to fuel cell electrodes

Abstract

Small scale solid particles with fl uid-fi lled pores are applied in various porous structures in energy systems, such as fuel cells, for the objectives to enhance the catalytic reaction activities and improve the fuel utilization effi ciency or/and reduce the pollutants. In addition to the catalytic reactions, heat transfer processes in fuel cell porous electrodes are strongly affected by the small scale and complex porous structures. In this paper, the thermal energy equation commonly used for continuum models at porous-averaging level is highlighted, with the purpose to provide a general overview of the validity and limiting conditions for its application. Models for effective thermal conductivity are reviewed and discussed. It is found that both the rarefaction and tortuosity effects on reduction of effective thermal conductivity may be signifi cant, and these should be evaluated based on detailed information of operating parameters, pore size distributions and topologic structures. Comments and suggestions are presented for the better understanding and implementation of the continuum heat transfer models for fuel cell electrodes.

Numerical Simulation of the Transport of Gas Species in the PVT Growth of Single‐Crystal SiC

“…For the porous medium, including the source powder and thin porous graphite sheet, the effective volumetric heat capacity $${( {\rho {C}_{\mathrm{p}}} )}_{{\mathrm{eff}}}$$ is calculated as [ 32 ] $$$$\begin{equation}{\left( {\rho {C}_{\mathrm{p}}} \right)}_{{\mathrm{eff}}} = \ \left( {1\ - \ {\varepsilon }_{\mathrm{p}}} \right)\ {\rho }_{\mathrm{s}}\ {C}_{{\mathrm{ps}}} + \ {\varepsilon }_{\mathrm{p}}\ {\rho }_{\mathrm{f}}\ {C}_{{\mathrm{pf}}}\end{equation}$$$$where $$\ {\varepsilon }_{\mathrm{p}}$$ is the porosity of the porous medium, $$\ {\rho }_{\mathrm{s}}$$ is the solid matrix density, and $$\ {C}_{{\mathrm{ps}}}$$ and $$\ {C}_{{\mathrm{pf}}}$$ are the solid matrix heat capacity and fluid heat capacity at constant pressure, receptively. The effective thermal conductivity $${k}_{{\mathrm{eff}}}$$ is given by [ 33,34 ] $$$$\begin{equation}{k}_{{\mathrm{eff}}} = \ \left( {1\ - \ {\varepsilon }_{\mathrm{p}}} \right){k}_s + {\varepsilon }_{\...$$…”