介质黏度对泵作透平时性能换算的影响

Effect of medium viscosity on performance conversion of pump as turbine

为了研究泵与透平换算系数随黏度与比转数的变化规律,选用5台不同比转数离心泵反转作透平,在5种不同的介质黏度下,对透平工况进行数值模拟.根据数值模拟结果,拟合求得透平的压头、效率与流量的关系式.通过对透平效率-流量关系式的求导,可得到透平在最优效率点处的流量、压头.据此可以求得泵反转作透平时,透平在黏性介质时的最优工况下的流量、压头与水泵在清水介质最优工况下流量、扬程之间的换算系数.通过黏性介质下透平的水力效率、压头与流量关系曲线发现:介质黏度对透平性能的影响较大,随介质黏度的增大,透平的水力效率明显下降.比较不同比转数下的换算关系随黏度变化曲线图可发现:对于同一比转速的透平,换算系数均随黏度的增大而增大;而当介质黏度相同时,随着比转数的增大,流量、扬程换算系数大体呈减小趋势.

In order to study the variation characteristics of performance conversion factors of pump and turbine with viscosity and specific speed, centrifugal pumps with five different specific speeds were chosen as pump and turbine. The flows in the turbines were numerically simulated at five different vis- cosities. Based on simulated results, the mathematical relationships such as head- flow rate and effi- ciency- flow rate are obtained with curve fitting. Then the head, efficiency and flow rate are decided at the best efficiency point where the slope of the efficiency curve with respect to flow rate is zero. Eventually, flow rate, head and efficiency conversion factors are calculated based on the flow rate, head and efficiency are at a viscosity higher than water and those at the viscosity of water are at best ef- ficiency points. It is shown that medium viscosity has a greater influence on turbine performance, par- ticularly, the hydraulic efficiency of turbine decreases evidently with increasing viscosity. At the same specific speed, the conversion factors rise with increasing viscosity. At the same viscosity, the conver- sion factors reduce generally with increasing specific speed.