Research On Conversion Relation And Internal Loss Of Centrifugal Pump As Turbine In Viscous Medium

In the process industries such as petrochemical and coal chemical industries,it contains a large amount of high-pressure liquids with a viscosity greater than 1centipoise,and most of these liquids have a certain amount of energy.However,in the traditional process industry,the energy consumption of these liquids is achieved through pressure relief valves and other measures to meet the needs of the next process.In recent years,due to the country's emphasis on energy-saving emission reduction and basic theoretical research on hydraulic turbines,the reversal of centrifugal pumps as hydraulic turbines has been successfully applied in the chemical process industry with a medium viscosity.However,there have been studies on the pump head/head and flow conversion coefficients of the pump reverse operation under the viscous medium,and the research on the relationship between the efficiency and power conversion of the low specific speed centrifugal pump as the turbine under the viscous medium has not been reported.At present,for the study of the internal hydraulic loss of turbines,some scholars have found that the hydraulic loss of the hydraulic turbine draft tube cannot be ignored,and there is a draft vortex in the turbine draft tube that rotates in the same direction as the impeller,that is,the fluid in the draft tube has a certain circumference Minute speed.At the same time,it is pointed out that the influence of the kinetic energy loss caused by the circumferential partial velocity of the turbine draft tube on the hydraulic efficiency of the hydraulic turbine is not negligible,but it does not explain how to eliminate the circumferential partial velocity and thereby reduce the kinetic energy loss of the draft tube.To this end,this article does the following:1.This article selects 5 sets of pumps with different low specific speeds as turbines in the pump manual of Shenyang Pumping Plant as the research object,and performs numerical simulation under 5 different viscosity media.The study found that for the same specific speed pump as a turbine,the maximum efficiency point of the turbine shifts to a large flow rate with the increase of viscosity,and the output power of the turbine under optimal operating conditions decreases first and then increases as the viscosity increases.The efficiency and power conversion coefficients of different low specific speed centrifugal pumps used as turbines under different viscosity media and the changes of these conversion coefficients with the impeller Reynolds number and pump specific speed changed.It was found that the efficiency conversion coefficient increased with the increase of the impeller Reynolds number Large;the power conversion factor decreases first and then increases as the Reynolds number increases.2.The efficiency conversion coefficient is expressed as a relational expression related only to the pump specific speed and the impeller Reynolds number.Within the scope of the study,the obtained relationship can accurately obtain the efficiency conversion coefficient between any low specific speed pump and a certain viscosity(viscosity range of 1mm~2/s~36mm~2/s)as the turbine and its pump operating conditions.In order to predict the efficiency of the pump as a turbine,it provides a reference for the selection of a centrifugal pump as a hydraulic turbine.3.Select the reverse rotation of the centrifugal pump with a specific speed of55.7 as the turbine as the research object,and analyze the hydraulic loss of the turbine's flow components under different viscosities.It is found that the hydraulic loss of the turbine impeller accounts for the largest proportion of the total hydraulic loss,and the viscosity Increase.The hydraulic turbine draft tube has both axial velocity and the same circumferential velocity as the impeller rotation direction;the hydraulic loss in the turbine draft tube decreases first and then increases as the flow rate increases.4.In order to reduce the fluid loss in the turbine draft tube,the circumferential component of the fluid in the draft tube must be eliminated.In this paper,a centrifugal pump with a specific speed of 55.7 is used as a turbine for the study.By adding a baffle to the turbine draft tube,the rotational movement of the liquid flowing from the impeller is eliminated,thereby reducing the hydraulic loss caused by the circumferential partial velocity.To this end,a variety of schemes are designed in this paper,and the numerical simulation of each scheme is carried out to obtain the scheme with the smallest fluid loss in the draft tube.Through the analysis of the numerical simulation results of the optimal scheme,it is found that the hydraulic turbine with the draft tube deflector added The output power is higher than the turbine without draft tube deflector,the hydraulic efficiency of the hydraulic turbine is higher than the turbine without draft tube deflector,the hydraulic efficiency of the turbine at the optimal working point(1.6Q)is increased by about 3.027%.5.Analysis of the internal flow field diagram of the hydraulic turbine with and without the draft tube deflector found that the addition of the draft tube deflector makes the streamline in the turbine draft tube flat,and the circumferential sub-speed decreases due to the circumferential velocity.The dynamic loss is then reduced;the addition of the draft tube deflector reduces the turbulent kinetic energy inside the impeller,improves the internal fluid flow state of the turbine,and reduces the turbine energy loss caused by the turbulent energy loss.