Proton exchange membrane fuel cells are a new energy technology with great potential due to advantages such as high efficiency and no pollution. The structure of the gas flow channels has a profound impact on the overall performance of the fuel cell. Different flow channel geometries have their own advantages and disadvantages, and a good understanding of the influence of these structures on performance can provide a reference for the design and improvement of flow channel geometries in various application contexts. Numerical models can be used as a reasonable and reliable tool to evaluate the influence of operating and structural parameters on cell performance and service time by simulating the transport processes of substances and heat as well as electrochemical reactions inside the fuel cell and can be used for the optimisation of cell design. This paper reviews the recent models of proton exchange membrane fuel cells, summarises and analyses the effect of gas flow channels on fuel cells, and organises and concludes efficient design of flow channel structures to enhance PEMFC performance in terms of the cross-section shape, length, width, number of flow channels, and baffle position.

This work aims at using Computational Fluid Dynamics (CFD) method to establish a gasoline direct injection (GDI) engine nozzle and combustion chamber model to simulate cavitation and flash boiling phenomena and analyze how these phenomena affect the engine performance. FLUENT 15.0 is used to simulate the flow of fuel. The cavitation phenomenon in GDI nozzle was simulated comprehensively, and the influences of parameter values such as inlet pressure and outlet pressure on cavitation were studied in this work. The results show that high injection pressure can promote the occurrence of cavitation and high outlet pressure has an inhibitory effect on cavitation. However, the effect of cavitation on atomization cannot be seen intuitively only through the simulation of the internal nozzle. The two-dimensional inter nozzle model established in this work is a foundation for the establishment of external nozzle model. It can provide specific boundary conditions at nozzle outlet. In addition, a three-dimensional external nozzle model was established to simulate the flash boiling spray in the combustion chamber. Based on the mechanism, it can be found that flash boiling spray improves the atomization quality. After verifying the simulation results with relevant experiments, these models could bring great convenience to the study of cavitation and flash boiling with sufficient reliability in further study.

This work aims to apply Computational Fluid Dynamic (CFD) method to establish a flash evaporation spray cooling (FESC) model to simulate the heating process and find the optimum cooling performance. The heat transfer process during FESC is studied through numerical simulation using commercial code ANSYS FLUENT. The species transport model and the discrete phase model are applied to simulate the multiphase flow and heat transfer process. The turbulence effect is included. The effects of flow rate, nozzle pressure, nozzle angle, and the nozzle orifice size on spray cooling are investigated through analyzing the final surface temperature distributions. This work revealed the mechanism of the heat transfer process in FESC by means of particle tracks and velocity magnitude distribution. The simulated results for the effect of flow rate were compared with other researchers’ previous published experimental results. The comparison shows same trend, which verified the model and the simulation result. The optimum cooling performance is found by analyzing various working conditions. The results show that high flow rate, high nozzle pressure, small nozzle angle and small nozzle orifice can improve the FESC characteristics. The detailed mechanisms of these effects under various working conditions are also discussed. Under giving working conditions, the optimum cooling performance is obtained for the condition where mass flow rate of working fluid is 2L/min, the nozzle pressure is 100MPa, the nozzle angle is 15 degrees and the orifice size of the nozzle is 1mm.