Two-dimensional Flow And Mass Transfer Model For Liquid-fed Direct Methanol Fuel Cell

Direct methanol fuel cell (DMFC) is a kind of cell which takes methanol into fuel cell, then with catalyzed electro chemical reaction to generate electricity. Compare to other types of fuel cell, DMFC has some significant advantages: quick start-up, easy to design, facility in fuel supply, high energy density, reliable operation etc., these features are facility to electric vehicle and removable power supply. But the detailed distributions of temperature, pressure, velocity, molar concentration and current density cannot be easily obtained experimentally. So the simulations of flow and mass transfer characteristics of DMFC are basically essential.Universal Darcy law has been used in this dissertation to describe the momentum conservation in the porous medium and non-porous medium. In allusion to numbers of working conditions, detailed distribution of flow parameters in cathode, anode and methanol crossover of parallel channel DMFC has been simulated, which provides theoretical evidence for the optimizing method to the structure and the operation condition, and it also establishes a platform for further researches.First of all, a two-dimensional steady-state multi-component transport model was proposed to investigate the anode flow and mass transfer processes in direct methanol fuel cell with a parallel channel. The model can predict the velocity, pressure, concentration and current density distributions in the anode. This paper discusses the effects of operating conditions and electrode structure parameters on the performance of fuel cell. Results showed (1) velocity of the liquid methanol solution behaves in parabolic pattern in axial direction, maximum velocity lean to interface of channel and diffuser layer; along with channel direction, velocity got low. (2) along with channel direction, pressure reduced gradually; (3)methanol distribution is uneven in channel; (4) with increasing inlet velocity, the concentration gradient of methanol increased; (5)with increasing inlet velocity, local current density increased, but when it reached 0.9 m/s, local current density decreased, if implied the DMFC has the optimized inlet velocity; (6)with the increasing concentration of inlet methanol, performance of the cell was improved, but at the given concentration, the performance was increased little.Secondly, crossover of methanol was investigated. Result indicated that (1)with the increasing methanol diffusivity of membrane, crossover of methanol decreased; (2)with higher current density, crossover of methanol increased; (3)thicker membrane resulted increasing methanol crossover ;(4)higher porosity leads to lower methanol crossover; (5)low current density, the effect of methanol crossover on cell performance was small, at high current density, the effect became greater.Lastly, a two-dimensional steady-state multi-component transport model for parallel channel of DMFC cathode was established to investigate the anode flow and mass transfer processes in DMFC cathode. The effect of inlet velocity on mass transfer was discussed. The results shows that: (1) oxygen mole fraction decrease along channel gradually; (2) smaller the entry velocity of mix gas, more sufficiency of oxygen reaction; (3)water mole fraction changes a little in catalyze layer; (4)velocity of oxygen change a little along the channel with a slight fluctuation; (5) maximum velocity of oxygen occur in mainstream, velocity changed a little near channel-diffuser layer domain, velocity vector in channel leaned to diffuse layer; (6)average current density has a little effect on voltage potential; (7)with increasing temperature, cell performance improved; (8)with increasing of diffuser porosity, cell performance improved, 0.4 may be the best.