Using nanofluids for proton exchange membrane fuel cell (PEMFC) cooling in automotive applications

摘要

The main focus of this PhD research project was to experimentally and theoretically study the effects of using nanofluids as PEMFCs coolants on the electrical and thermal performances of PEMFCs system with a view to applying PEMFCs in automotive applications. To study the PEMFCs cooling system theoretically, a computer simulation model has been developed consisting of the sub-models of PEMFCs stack, radiator, water pump and coolants in Matlab. All the sub-models were combined to simulate the overall performance of the PEMFC cooling systems (with different liquids used as coolants). The model can be applied for any capacity PEMFCs cooling system and able to size the radiator, convection heat transfer coefficient of the coolants and pumping power required to circulate the coolants in the cooling loop. The convection heat transfer coefficient enhancement predicted by the theoretical computer simulation model was found to be ~60% for 0.05 vol% concentration of nanofluids, while for 0.5 vol% concentration the enhancement was estimated to be ~74%. As the results of this enhancement, the reduction of the frontal area of the radiator was found to be ~26% by using 0.05 vol% concentration of nanofluids while this could only be increased slightly (i.e. further ~1%) for 0.5 vol% concentration of nanoparticles. With 0.05 vol% concentration, the required pumping power for circulating the required coolants (i.e. nanofluids) for extracting 2.1 kW heat from PEMFC increased by ~5% compared with when 50/50 water-EG was used as coolant in the system. This pumping power showed negligible further increase by increasing the concentration of nanoparticles from 0.05 vol% to 0.5 vol%. Along with the theoretical prediction of the thermo-physical properties of nanofluids, the sample nanofluids were prepared in the RMIT chemical engineering lab and their electrical and thermo-physical (i.e. thermal conductivity, viscosity, specific heat and density) properties were measured experimentally. The experimental data were used in the theoretical computer simulation model to compare the outputs of the model with those results obtained by using theoretical predicted properties of nanofluids. The experimental rig was developed based on the 2.4 kW PEMFCs with a view to investigating the electrical and thermal performances of the PEMFCs system. With a view to investigating the electrical and thermal performances of PEMFC system, the PEMFCs was run first with this 50/50 water-EG. Following the experiment with 50/50 water-EG, more experiments were conducted with 0.05 vol% and 0.5 vol% ZnO nanofluids, 0.5 vol% TiO2 and 0.5 vol% Al2O3 nanofluids. During the experiments with various coolants, the coolant mass flow rate and fuel cell inlet temperature were kept constant at the same operating point (i.e. 50 A) of the fuel cells. No variations in the polarisation curves were found while using 50/50 water-EG and different types of nanofluids indicating no electricity leakage due to using nanofluids as coolants. On the other hand, the experimentally obtained thermal performance data were used to validate the computer simulation results. The computer simulation model results were matched with the experimentally obtained PEMFCs results with acceptable errors (i.e. below 10%).