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ABSTRACT
In order to understand the complex transport phenomena in a passive direct methanol fuel cell (DMFC), a theoretical model is essential. The analytical model provides a computationally efficient framework with a clear physical meaning. For this, a non-isothermal, analytical model for the passive DMFC has been developed in this study. The model considers the coupled heat and mass transport along with electrochemical reactions. The model is successfully validated with the experimental data. The model accurately describes the various species transport phenomena including methanol crossover and water crossover, heat transport phenomena, and efficiencies related to the passive DMFC. It suggests that the maximum real efficiency can be achieved by running the cell at low methanol feed concentration and moderate current density. The model also accurately predicts the effect of various operating and geometrical parameters on the cell performance such as methanol feed concentration, surrounding temperature, and polymer electrolyte membrane thickness. The model predictions are in accordance with the findings of the other researchers. The model is rapidly implementable and can be used in real-time simulation and control of the passive DMFC. This comprehensive model can be used for diagnostic purpose as well.
Nomenclatures
| = | Molar concentration, mol cm–3 | |
| = | Specific heat, J mol–1 K–1 | |
| = | Effective diffusion coefficient, cm2 s–1 | |
| = | Fuel cell voltage, V | |
| = | Fuel cell standard voltage, V | |
| = | Rate of change of electromotive force with temperature, V K–1 | |
| = | Faraday’s constant, C mol–1 | |
| = | Grashof number | |
| = | Gibbs free energy change, J mol–1 | |
| = | Enthalpy change, J mol–1 | |
| = | Convective heat transfer coefficient, W cm–2 K–1 | |
| = | Latent heat of vaporization for water, J mol–1 | |
| = | Cell current density, A cm–2 | |
| = | Crossover current density, A cm–2 | |
| = | Reference exchange current density of methanol, A cm–2 | |
| = | Reference exchange current density of oxygen, A cm–2 | |
| = | Thermal conductivity, W cm–1 K–1 | |
| = | Characteristic length, cm | |
| = | Electro-osmotic drag coefficient | |
| = | Molar flux, mol cm–2 s–1 | |
| = | Nusselt number | |
| = | Pressure, Pa | |
| = | Prandtl number | |
| = | Heat generation, W cm–2 | |
| = | Heat flux, W cm–2 | |
| = | Universal gas constant, J mol–1 K–1 | |
| = | Cell internal resistance, cm2 S–1 | |
| = | Cell contact resistance, Ω cm2 | |
| = | Temperature, K | |
| = | Cell voltage, V | |
| = | Molar fraction, mol mol–1 |
Greek letters
| = | Transfer coefficient | |
| = | Coefficient of volume expansion, K–1 | |
| = | Thickness, cm | |
| = | Ionic conductivity of PEM, S cm–1 | |
| = | Porosity | |
| = | Overpotential, V | |
| = | Relative humidity of ambient air | |
| = | Dynamic viscosity, g cm–1 s–1 | |
| = | Kinematic viscosity, cm2 s–1 |
Superscripts and subscripts
| = | Anode | |
| = | Ambient | |
| = | Anode current collector | |
| = | Anode catalyst layer | |
| = | Anode diffusion layer | |
| = | Cathode | |
| = | Convection mode of heat transfer | |
| = | Cathode current collector | |
| = | Cathode catalyst layer | |
| = | Cathode diffusion layer | |
| = | Methanol | |
| = | Oxygen | |
| = | Polymer electrolyte membrane | |
| = | Water | |
| = | Reference value | |
| = | Reservoir | |
| = | Generation |
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