Entropy production analysis for energy dissipation of a vertical mixed-flow pump device under asymmetric inflow conditions

Abstract

To investigate the influence of the inflow angle on the hydraulic loss and internal flow fields of a vertical mixed-flow pump device, unsteady numerical simulations were performed under different inflow angles ( θ = 0°, 10°, 20°, and 30°). The calculation results were validated using an external characteristic test at an inflow angle of 0°. The entropy production theory was applied to analyse the energy loss and dissipation rate distribution in a vertical mixed-flow pump device under different inflow angles. Influenced by asymmetric inflow, the design point of the external characteristics deviated towards the overload flow rate, and the maximum deviations were obtained under 1.2 Qdes, whereas the influence of the inflow angle on the internal flow fields was the most significant under the part-load flow rate. When the inflow angle increased from 0° to 30°, the total entropy production in the pump device increased by 18.35% under 0.6 Qdes, and indirect dissipation accounted for the largest proportion. The internal flow patterns in the impeller and guide vane were also distorted by asymmetric inflow. The indirect dissipation rate on the suction side of the impeller blade, interface between the impeller and diffuser, and pressure side of the guide vane increased significantly with an increase in the inflow angle. To restrain the influence of asymmetric inflow, it is of great significance to optimise the hydraulic design structure of the inflow runner. In this study, a middle spacer pier was used to improve the operational efficiency of the pump device.

Entropy Production Analysis of a Vertical Mixed-Flow Pump Device with Different Guide Vane Meridians

“…Since the specific heat capacity of water is large, the temperature can be considered constant during the operation of the pump device, so the entropy production in the pump device is only determined by dissipation. Dissipation is mainly composed of three parts: the direct dissipation can be calculated by Equation (1) [ 20 ]; the indirect dissipation can be calculated by Equation (2) [ 20 ]; and the wall dissipation can be calculated by Equation (3) [ 21 ]: where , , represents the time-averaged velocities in the x, y, z directions, respectively; , , stand for fluctuating velocities in the x, y, z directions, respectively; represents temperature and represents fluid viscosity.…”

“…The other CFD-based mixed-flow pump device studies have centered on the hydraulic coherence between the guide vane and the outlet channel. Zheng et al [ 20 ] studied the distribution characteristics of the hydraulic loss of mixed-flow pump devices under different inflow angles. The results showed that with the increase of the inlet angle, the interference effect between the outlet channel and guide vane was weakened, which resulted in an increase of hydraulic loss in the outlet channel.…”