Numerical optimization of evaporative cooling in artificial gas diffusion layers

Abstract

The utilization of evaporative cooling in the gas diffusion layers (GDLs) of fuel cells or electrolyzers can effectively dissipate the heat produced by high power density operation, thus leading to economically more competitive electrochemical cells. The highly porous GDLs offer a large surface area, allowing to cope with larger heat fluxes and leading to larger evaporation rates. The understanding of the best GDL structure and cell operating conditions for optimized cooling is difficult to determine, given the complexity of the multi-physical processes involved. A direct pore-level numerical modeling framework was developed to analyze the heat and mass transport phenomena occurring within GDLs with integrated evaporative cooling. A three-dimensional model was developed that solves the Navier-Stokes equations, species transport and energy conservation equations in the gas domain, and energy conservation equations in the stagnant fluid phase and solid phase. Evaporation at the liquid-vapor interface was modeled using kinetic theory. The GDL geometry was approximated by an artificial lattice so as to enable the analysis of the effect of a systematic change in the geometry on the transport and evaporation characteristics. A parametric study indicated that increasing the GDL’s porosity from 0.8 to 0.9 and the operating temperature from 60°C to 80°C led to an increase of the evaporation rate of 19.9% and 197%, respectively. Changing the thermophysical properties of the carrier gas (air to hydrogen) enhanced the evaporation rate, and therefore the cooling of the GDL, by a factor 2.7. The decrease of the amount of vapor in the carrier gas at the water-gas interface impacted positively the evaporative cooling in the GDL.