Thermal and hydrodynamic performances of chaotic mini-channel: Application to the fuel cell cooling

Currently, heat exchangers allowing the thermal management of low-temperature fuel cells (PEMFC) are integrated in the bipolar plates and are constituted of a network of straight channels. The flow regime is laminar and thus unfavorable to intense convective heat transfer. In order to increase the power density of the fuel cells, the use of chaotic geometries in the cooling system is envisaged to promote high convective heat transfer. In the present study, several chaotic three-dimensional mini-channels of rectangular cross-section (2 millimeters x 1 millimeter) are evaluated in terms of heat transfer efficiency, mixing properties, and pressure losses. Their performances are compared both to those of the straight channel geometry currently used in the cooling systems of the PEMFC and those of a square-wave mixer. Two Reynolds numbers are considered: 100 and 200. It is shown that a 3-D chaotic channel geometry significantly improves convective heat transfer over that of regular straight or square-wave mixer channels. Of all the geometries studied, one induces higher heat transfer intensification (mean Nusselt number equal to 20) with a strong pressure loss. With an alternative geometry, a better compromise between heat transfer and pressure loss is obtained. However, all of the chaotic geometries present similar mixing rate for the two Reynolds numbers studied.