Study on the wall film behavior and droplet catching performance of a micro cyclone in hydrogen fuel cells

In hydrogen fuel cells, the separator used for hydrogen dehydration plays an important role in water management and hydrogen recovery. A dedicated micro -cyclone separator was proposed for the small space of the separator, low gas flow rate, and reduced allowable pressure. Based on the Euler-Lagrange method with hydrogen gas as a continuous phase and droplets as a discrete phase, the flow field and liquid film behavior inside the separator were numerically simulated with hydrogen as the continuous phase and liquid droplets as the discrete phase. The Eulerian Wall Film (EWF) Model was used for the liquid film simulation. It was described by the VOF model that a liquid pool was formed when the liquid film accumulates to a certain level. In the experiments, air was used as an alternative medium to hydrogen to verify the reliability of the simulation method. On this basis, the effect of main factors (e.g., the cone angle and the inlet velocity on the flow field, liquid film behavior, and droplet capture performance in the micro -cyclone separator) were explored The results show that at a certain inlet velocity, the increase of the cone angle enhances the tangential velocity of the continuous phase and increases the short-circuit flow rate and pressure drop, while the separation efficiency first increases and then decreases. The separation efficiency increases slightly with the increase of inlet velocity because only the escape of liquid droplets from the vortex finder is considered. Meanwhile, the separation efficiency decreases sharply with the increase of inlet velocity when the escape of liquid film from the vortex finder is also considered. These findings have important implications for water management in low-pressure drop micro -cyclone separators for hydrogen fuel cells.