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ABSTRACT
The heat and mass transfer characters of proton-exchange membrane (PEM) fuel cell have major impact on the performance of cell system, and suitable moisture content in the membrane is one of the most important enhancing factors of PEM fuel cell systems. In this article, the effect to different vaporization mechanism of water in the membrane is investigated numerically, the results show that the temperature of the fuel cell increases with lessens of the heat transfer coefficient, and the average temperature located in membrane is reduced most significantly by 18.03% compared to no vaporization condition in membrane for cases in which heat transfer coefficient is 50 W/m2 · K. Furthermore, the current density with evaporation in membrane is much lower than take no account of vaporization, especially on the cathode side; meanwhile, the excess percentage of oxygen and water vapor concentration is more significantly different from the condition without vaporization when the fuel cell temperature reaches the boiling point.
Nomenclature
| L | = | geometric length (m) |
| H | = | geometric height (m) |
| W | = | geometric width (m) |
| I | = | current density (A/m2) |
| u | = | fluid velocity (m/s) |
| j | = | transfer current density (A/m3) |
| M | = | molecular weight (kg/mol) |
| F | = | Faraday constant (96,487 C/mol) |
| k | = | thermal conductivity (W/m · K) |
| w | = | mass fraction (%) |
| K | = | thermal resistance (K/W) |
| x | = | mole fraction (%) |
| D | = | mass diffusivity (m2/s) |
| T | = | temperature (K) |
| R | = | universal gas constant (8.314 mol/K) |
| C | = | molar concentration (mol/m3) |
| P | = | pressure (Pa) |
| CP | = | specific heat capacity (J/kg · K) |
| Eeq | = | equilibrium potential (V) |
| Greek symbols | = | |
| ρ | = | density (kg/m3) |
| ε | = | porosity |
| µ | = | dynamic viscosity (kg/m · s) |
| κ | = | permeability (m2) |
| = | Forchheimer drag option (kg/m4) | |
| σ | = | conductivity (S/m) |
| η | = | overpotential (V) |
| α | = | electrical transfer coefficient |
| τ | = | tortuosity |
| Subscripts and superscripts | = | |
| c | = | gas channel |
| m | = | mass |
| GDL | = | gas diffusion layer |
| e | = | evaporation |
| me | = | membrane |
| H2 | = | hydrogen |
| O2 | = | oxygen |
| H2O | = | water |
| N2 | = | nitrogen |
| a | = | anode |
| c | = | cathode |
| s | = | solid |
| pc | = | phase change |
| o | = | standard condition |
| H | = | heat source |
| loc | = | location |
| eff | = | effective |
| ref | = | reference |
| cl | = | catalytic electrode |
| l | = | liquid |
| z | = | species index independently of i |
| i | = | species index |
Nomenclature
| L | = | geometric length (m) |
| H | = | geometric height (m) |
| W | = | geometric width (m) |
| I | = | current density (A/m2) |
| u | = | fluid velocity (m/s) |
| j | = | transfer current density (A/m3) |
| M | = | molecular weight (kg/mol) |
| F | = | Faraday constant (96,487 C/mol) |
| k | = | thermal conductivity (W/m · K) |
| w | = | mass fraction (%) |
| K | = | thermal resistance (K/W) |
| x | = | mole fraction (%) |
| D | = | mass diffusivity (m2/s) |
| T | = | temperature (K) |
| R | = | universal gas constant (8.314 mol/K) |
| C | = | molar concentration (mol/m3) |
| P | = | pressure (Pa) |
| CP | = | specific heat capacity (J/kg · K) |
| Eeq | = | equilibrium potential (V) |
| Greek symbols | = | |
| ρ | = | density (kg/m3) |
| ε | = | porosity |
| µ | = | dynamic viscosity (kg/m · s) |
| κ | = | permeability (m2) |
| = | Forchheimer drag option (kg/m4) | |
| σ | = | conductivity (S/m) |
| η | = | overpotential (V) |
| α | = | electrical transfer coefficient |
| τ | = | tortuosity |
| Subscripts and superscripts | = | |
| c | = | gas channel |
| m | = | mass |
| GDL | = | gas diffusion layer |
| e | = | evaporation |
| me | = | membrane |
| H2 | = | hydrogen |
| O2 | = | oxygen |
| H2O | = | water |
| N2 | = | nitrogen |
| a | = | anode |
| c | = | cathode |
| s | = | solid |
| pc | = | phase change |
| o | = | standard condition |
| H | = | heat source |
| loc | = | location |
| eff | = | effective |
| ref | = | reference |
| cl | = | catalytic electrode |
| l | = | liquid |
| z | = | species index independently of i |
| i | = | species index |