Energy Characteristics of Full Tubular Pump Device with Different Backflow Clearances Based on Entropy Production

In this study, the entropy theory was used as the evaluation standard of energy dissipation, and the effect of backflow clearance (the gap between motor rotor and motor shell) on energy characteristics of a full tubular pump was investigated by 3D unsteady flow simulation. The calculated results validated through testing shows that backflow clearance produces additional head loss and the rotation of the motor rotor requires more shaft power. The additional energy losses lead to a significant decline in the efficiency of tubular pump device. Under design conditions, the total dissipation of backflow clearance, rear guide vane, and outlet passage decreases with the increase of clearance radius, but that of the impeller decreases first and then rises with the increase of clearance radius. In addition, the increase of the clearance radius leads to disorderly flow pattern in the impeller. The total dissipation rate on the impeller suction side and near the impeller inlet increases with the increase of backflow clearance radius, but that on the impeller suction side decreases with the increase of backflow clearance radius. The total dissipation rate of the suction side of the guide vane and the wall of the outlet passage decreases with the increase of backflow clearance radius. This work can provide an intuitive analysis of the energy dissipation caused by backflow clearance and reference for engineering applications of full tubular pump.