Three-dimensional CFD Simulation of a Roots Blower for the Hydrogen Circulating Pump

Fuel cell vehicle (FCV) is more advantageous compared to a gasoline-powered internal combustion engine based vehicle and is a new and popular way to solve the environmental problem. Hydrogen circulating pump is an essential assembly unit for the fuel cell, which is used in FCV. Roots blower is employed in this field. Hydrogen has a low molecular weight, which means it is easy to leak through the clearances and hard to preserve. It increases the difficulty of design and operation. In this paper, the performance parameters of a three-lobe roots blower were studied. A multi-scale model was used since the clearance, compared with the rotor diameter, is quite small and easy to induce gas leakage. The long pipes and the throttle values were included in this model. To improve the accuracy and the mesh quality, the working chambers and clearances were represented by highly deforming dynamic structured grids and the grids of the clearances had a high density. The suction and discharge ports were meshed by static unstructured grids. The interfaces were used between the two rotors and between the rotors and the suction and discharge ports. The performances were compared at three different rotational speeds of 4500 rev/min, 6000 rev/min and 8000 rev/min using hydrogen as the working fluid in this numerical model with almost the same inlet and outlet pressures. Meanwhile, the effect of the leakage was also analyzed using two different clearances, which had an important influence for the designing and using of the roots blower