Al2O3–H2O nanofluids for cooling PEM fuel cells: A critical assessment

Polymer electrolyte membrane (PEM) fuel cells are promising eco-friendly and sustainable power generation technology. Thermal management of these cells is one of the main challenges facing their commercialization. Alumina nanofluids, in addition to others, have been proposed to overcome excess heat generated within the PEM fuel cell stacks. However, most the previous studies investigated the hydrothermal performance of the nanofluids as a function of Reynolds number (Re). It is evident that all parameters must be kept constants except one to examine its effect on the performance. To this end, choosing Re as a parameter (independent variable) is problematic as it is a function not only of nanofluid's velocity, but also its density and viscosity. In this study, a well-validated CFD model has been built to simulate the hydrothermal performance of alumina nanofluids of different volumetric concentrations (0%, 0.05%, 0.1% and 0.2%) as functions of Re (170 < Re < 530), flow rate (20 ml/min ≤ Vf ≤ 50 ml/min), and pumping power (0.025 mW < Pp < 0.3 mW). This study shows a maximum reduction of 7.9% in the thermal effectiveness and a maximum increase of 6% in the pumping power when using the nanofluids instead of water. This deterioration in the hydrothermal performance is due to the reduction in the effective specific heat capacity and increase in viscosity of the nanofluids. Also, it is concluded that it is incorrect to use Re as an independent variable in analysing the hydrothermal performance of nanofluids because of the dependency of Re on some of the thermophysical properties of the nanofluids, which are functions of the concentration. Adopting such analysing procedure leads to false conclusions