A pump is not ideally designed to operate as a turbine. To improve the efficiency of a pump as turbine (PAT), the redesign of the PAT, according to the flow of the turbine, is required. The blade wrap angle is one of the main geometric parameters in impeller design. Therefore, an investigation into the blade wrap angle to the PAT’s influence can be useful. In order to understand blade wrap angle to the influence of the PAT, this paper numerically investigated three different specific speeds of PATs with different blade wrap angles. The validity of numerical simulation was first confirmed through a comparison between numerical and experimental results. The performance change of the PATs with the blade wrap angle was acquired. A detailed hydraulic loss distribution and a theoretical analysis were performed to investigate the reasons for performance changes caused by the blade wrap angle. The results show that there is an optimal blade wrap angle for a PAT to achieve the highest efficiency and the optimal blade wrap angle decreases with an increasing specific speed. A performance analysis shows the PAT’s flow versus pressure head (Q-H) and flow versus generated shaft power (Q-P) curves are lowered with the decrease of the blade wrap angle. The hydraulic loss distribution and theoretical analysis illustrate that it is the decrease of hydraulic loss within the impeller, together with the decrease of the theoretical head, that results in the performance decrease. The decrease of hydraulic loss within the impeller is attributed to the shortened impeller blade passage and the reduced velocity gradient within the impeller flow channel. With the decrease of the blade wrap angle, the slip factor of the PAT’s impeller is decreased; therefore, its theoretical head is also decreased.

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The effects of microgrooves and microdimples on the load-carrying performance of mechanical gas seals are compared in this study. Numerical model based on the Reynolds equation for compressible Newtonian fluid is utilized to investigate the load-carrying performance including the hydrodynamic pressure, the load-carrying force, and gas film stiffness of the gas seals. The results indicate that both microgrooves and microdimples can improve the load-carrying performance of mechanical gas seals, particularly under a small clearance condition. Furthermore, different texture patterns achieve optimal load-carrying performance at different area density, seal clearance, and depth: microgrooves with a low area density can obtain higher load-carrying force and gas film stiffness than the dimple patterns, but with high area density, elliptical dimples yield better load-carrying performance than the groove patterns.

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The two-phase solid-liquid flow in the computational fluid dynamic (CFD) method is generally analyzed by treating the solid particles as a quasi-fluid element, but this does not take into account the effects of the physical features of the solid particles and collisions among the particles. In this study, the discrete element method (DEM) was coupled with the CFD method in order to analyze the transient two-phase solid-liquid flow in a single-stage centrifugal pump with consideration for the particle-particle and particle-structure interactions. The numerical simulation process involving EDEM and FLUENT is described. Simulations were performed for the water at 25âĎČ at the continuous phase together with 15% of the volume as spherical solid particles (density ρ = 1500 kg/m 3 ) with the diameter ranging from 1 to 3 mm in a random order. The results illustrate the motion of the solid particles in the pump and their effect on the flow performance of the pump in terms of time variation in the head. The velocity fields for the two-phase flow together with the volume fraction distributions and trajectories of the solid particles in the centrifugal pump are also presented.