Flow Distribution Uniformity Evaluation in kW-Range Direct Methanol Fuel Cell Stack
This paper describes evaluation of flow distribution uniformity in DMFC stack. The DMFC stack has 70 cells with different manifold cross-section area of 500mm2 or 1500mm2. Two flow patterns of U-configuration and Z-configuration are used. Bi-polar plate active area is 180cm2 with 30 serpentine channels. Channel is 400mm-long with cross-section area of 0.6875mm2. We performed flow network analysis of DMFC by using manifold flow model combined with cell channel flow. Cell channel flow is modeled by Hagen-Poiseuille equation. Manifold flow is modeled by mechanical energy conservation equation. Different flow rates are considered 180L/min or 360L/min. Case.1: U-configuration, 180L/min, 500mm2, Case.2: U-configuration, 360L/min, 500mm2, Case.3: Z-configuration, 360L/min, 500mm2, Case.4: U-configuration, 360L/min, 1500mm2. As flow rate increased from 180L/min to 360L/min, turbulent flow effect in manifold increases. Pressure drop in manifold of case.2 is about 3.8 times larger than that of case.1. As a result, serious non-uniform flow distribution happens in case.2. In comparison between Z-configuration and U-configuration, pressure drop in manifold of case.3 is lower than that of case.2. Z-configuration is more desirable than U-configuration. As manifold crosssection area increasing to 1500mm2 in case.4, pressure drop in manifold of case.4 becomes about one-eighth of that of case.2, which results in more uniform flow distribution. In summary, large pressure drop in manifold is caused by turbulent flow resulting in more serious non-uniform flow distribution in U-configuration. Zconfiguration helps to reduce pressure drop in manifold and non-uniform flow distribution for each cell. Manifold cross-section area also has significant effect on flow distribution uniformity.