Research On Performance Conversion And Energy Loss By Pump As Turbine Under Different Viscosities

In petrochemical,petroleum processing,coal chemical and other process indus-tries,there are a large number of liquids with high-pressure energy.Most of these liq-uids with high-pressure energy have a certain viscosity.At present,these high-pressure liquids are generally depressurized by pressure reducing valves to achieve the pressure required by the follow-up process.The pressure energy of high-pressure liquids is con-sumed in the form of heat energy.In recent years,due to the great progress in the basic theoretical research of hydraulic turbines with water as medium,the use of pump as turbine(PAT)and the design of special hydraulic turbines have been successfully ap-plied in some chemical process industries with less viscosity(when the viscosity is less than 5 mm~2/s,the influence of viscosity on the performance of hydraulic turbines is less).However,in the process industry with high viscosity(when the viscosity is greater than 5 mm~2/s),there is no report of successful operation of hydraulic turbines in viscous media due to weak research foundation.This is because there is no conver-sion relationship between the head,flow rate,efficiency and power of centrifugal pumps reversing as hydraulic turbines with different viscosities and specific speeds under the optimal operating conditions.Which makes it impossible to select pumps as hydraulic turbines in viscous media.Therefore,it is necessary to study the conversion coefficients of head,flow rate,efficiency and power of centrifugal pumps with differ-ent specific speeds reversing as turbines under the optimal working conditions and in viscous media,and the relationship between these conversion coefficients and specific speeds and Reynolds number of impellers.In viscous media,the pressure head of hy-draulic turbine decreases with the increase of viscosity,and the internal hydraulic loss increases.Therefore,it is necessary to study the internal loss law of hydraulic turbine and its overflow components.Five low specific speed pumps reversing as turbine were selected as the research objects.Firstly,numerical simulation and experimental results were compared in nor-mal temperature and clear water medium to verify the accuracy of numerical simulation.Then numerical calculation was carried out in four other low viscosity media.The nu-merical calculation results are processed and analyzed,and the conversion relationship of pump as turbine in viscous medium is obtained,and the variation law of slip coeffi-cient and hydraulic loss of flow passage components in different viscous media is obtained.The main research contents and results are as follows:1.Variation of Turbine Conversion Coefficient in Viscous Media.For the same specific speed pump as turbine,with the increase of working medium viscosity,the optimal efficiency point of the turbine shifts to the condition of large flow rate,and the flow rate,pressure head conversion coefficient decreases with the increase of the Reyn-olds number of the impeller.2.The conversion coefficients of head and flow rate are only related to the spe-cific speed of the pump and the Reynolds number of the impeller under the optimum working conditions of the pump inversing as a hydraulic turbine in viscous medium.It lays a foundation for the selection of turbines with pump in different viscous media.The example shows that the conversion formula can be used to select the type of pump as turbine accurately.3.Taking a centrifugal pump as turbine with specific speed of 55.7 as the research object,it is obtained that the slip coefficient of the impeller increases with the increase of medium viscosity at the same flow rate,decreases with the increase of flow rate at the same viscous medium.It can be seen that the viscous medium increases,and the function force of turbine impeller decreases.and increases with the increase of medium viscosity at the optimal operating point of the same specific speed pump.4.Taking the centrifugal pump as turbine with specific speed of 55.7 as the re-search object,it is obtained that the hydraulic loss of impeller in turbine decreases first and then increases with the increase of flow rate and reaches the minimum at the opti-mum operating point in the same viscous medium;the hydraulic loss of draft tube de-creases first and then increases with the increase of flow rate in the same viscous me-dium;and the hydraulic loss of impeller increases with the increase of medium viscos-ity at the same flow rate.The internal hydraulic loss of impeller plays a dominant role in the total hydraulic loss of turbine.With the increase of medium viscosity,the ratio of internal hydraulic loss of volute to total loss increases obviously.In the optimization design of turbines with high viscosity,the performance of volute and impeller should be improved simultaneously.5.Taking a centrifugal pump as turbine with a specific speed of 55.7 as the re-search object,the turbulent kinetic energy distribution in the middle section and the velocity streamline distribution in the middle section are analyzed.The results show that the turbulent kinetic energy distribution in the optimum working condition of a centrifugal pump as turbine with different medium viscosities is the similar.The turbulent kinetic energy region is mostly concentrated on the back of the blade and a small part is located on the working face of impeller inlet in the turbine.The fluid flow near the middle line of the flow passage is stable;in the optimum condition of the velocity streamline distribution chart of the middle section,there are a few vortices near the working face at the inlet of the turbine impeller and the scale of the vortices is small.