Effect of Velocity Slip on Head Prediction for Centrifugal Pumps as Turbines

Xiaohui Wang,Zhengting Xia,Junhu Yang,Xiaorui Cheng,Yan Hao

doi:10.1155/2019/5431047

Xiaohui Wang, Zhengting Xia + Show 3 more

Open Access

https://doi.org/10.1155/2019/5431047

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Abstract

The application of pumps as turbines (PAT) has been developed in several applications for energy recovery schemes. Therefore, establishing a performance correlation between pump mode and turbine mode is essential for selecting the proper machine. However, slip phenomenon is the challenges of head prediction for PAT. In this paper, the slip phenomenon of pump and PAT was revealed, and the slip factor was studied using CFD. The effect of slip on head prediction for PAT was analyzed, and a theoretical prediction model was presented considering slip factors. In order to validate the head prediction model, six centrifugal pumps with specific speed (ns) from 9 to 54.8 were tested as turbines. Results showed that the predicted head by the proposed method was in good agreement with the experimental data, and it is more accurate than Stepanoff, Alatorre-Frenk, Sharma, and Derakhshan models. This method can be applied in head prediction for low specific speed PAT ( ns <60).

Highlights

Centrifugal pumps operating as turbines (PAT) are an attractive and important alternative for energy recovery solution
Two pressure transmitters ABG-M2 with range of 0-2MPa were set at the inlet and outlet of PAT, respectively, for measuring pressure, an electromagnetic flow meter MF200-101 was set at the inlet pipe of PAT for measuring the discharge, and a NJ1 torque meter was installed at PAT shaft for measuring the rotational speed and torque of PAT
It was observed that the relative velocity increased uniformly along the blade of suction side for both pump and PAT, and humped for pressure side, which was caused by slip phenomenon within flow passages

Summary

Introduction

Centrifugal pumps operating as turbines (PAT) are an attractive and important alternative for energy recovery solution. There have been several prediction techniques published so far, as reported by Stepanoff [2], Alatorre-Frenk [3], Sharma [4], Williams [5], Singh [6], Derakhshan, and Nourbakhsh [7, 8], Wang [9], and Ramos [10] Most of these studies have suggested the relations for prediction of PAT behavior either based on efficiency or based on specific speed in pump mode, and a few have derived the relations based on experimentation. In order to predict the performance characteristics, velocity slip within flow passages should be considered both in pump and in turbine modes, and the slip factor was calculated by means of numerical simulation in their papers [15, 16].

Theoretical Analysis

Numerical Investigation

Results and Discussion

Conclusion