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Study On The Influence Law Of Medium Specific Speed Impeller Cutting On Turbine

Posted on:2021-05-06Degree:MasterType:Thesis
Country:ChinaCandidate:Y LiFull Text:PDF
GTID:2392330623983909Subject:Power engineering
Abstract/Summary:PDF Full Text Request
Saving energy is the only way for social progress.In the process industry,there are often a large number of high pressures,and a certain amount of liquid has not been fully recovered and utilized,and pump reversal as a turbine is the main way to recover this energy.However,a pump currently has only 30 specifications at most,which can not meet the needs of industrial processes to choose hydraulic turbines.Therefore,the outer diameter of the impeller can be cut to meet the needs of hydraulic turbine selection.In addition,reversing the pump as the turbine generally selects the pump of medium and low specific speed,so the research chooses the reversing of the medium and low specific speed pump as the hydraulic turbine.In this project,four medium specific speeds and four low specific speed centrifugal pumps were selected as hydraulic turbines.The specific speeds of the medium specific speed pumps were 84.5 ? 92.8 ? 125.3 and 129.3,and the specific speeds of the low specific speed pumps were respectively 33?47?69 and 78,and then,without changing other geometric dimensions,the outer diameters of the impellers of8 pumps as turbines were cut to varying degrees,of which the ratio of the intermediate specific speed pumps as turbines was 3 %?6%?9% and 12%,and the low specific speed pump for turbine cutting rate is 3%?6%?9%.Using FLUENT software to numerically simulate the 8 turbine models under the impeller prototype and different cutting rates,the following conclusions can be obtained:1.The impact of cutting medium and low specific speed impellers on the performance of the pump turbine is as follows: for each medium and low specific speed pump as a turbine and its turbine models with different cutting rates,the efficiency is first as the flow rate increases After increasing,the pressure head and shaft power increase with the increase of the flow rate;and as the cutting rate increases,the flow point of the optimal efficiency point of each turbine has been shifted to the small flow point,the pressure of the optimal efficiency point The power of the head and shaft gradually decreases,but with the increase of the cutting rate,the flow rate,shaft power and reduction of the pressure head of the different specific speed pump as the optimal efficiency point of the turbine are different.2.In order to expand the use range of medium and low specific speed pumps as turbines,by comparing the flow rates,indenter ratios and shafts of different medium and low specific speed pumps and pumps as turbines at the optimal efficiency pointsof different cutting rates The change rule of the power ratio is available.For each medium and low specific speed pump and pump as turbine,as the cutting rate increases,the pump and pump act as the turbine's optimal efficiency point of the flow ratio,head ratio and shaft power ratio It gradually decreases,and with the increase of the cutting rate,the flow rate ratio,indenter ratio and shaft power ratio of the pumps with different specific speeds and turbines at the optimal efficiency point of the turbine are different.Among them,the medium specific speed pump and the pump are used as turbines,and the cutting rate is between 0% and 9%.The reduction rate of the optimal efficiency point flow ratio,indenter ratio and shaft power ratio of each pump and pump is small.When the cutting rate is 12%,the reduction is large,and the low specific speed pump and pump are used as the turbine,and the cutting rate is between0% and 6%.Each pump and pump are used as the turbine's optimal efficiency point flow ratio,pressure The reduction ratio of the head ratio and the shaft power ratio is small,and when the cutting rate is 9%,the reduction amount is large.3.With the increase of cutting rate,the total hydraulic loss increases,and the hydraulic loss of flow passage components such as impeller and volute also increases,and the hydraulic loss of impeller with the increase of cutting rate is the largest,while the change of draft tube with the increase of cutting rate is not obvious.4.From the mid-section velocity streamline diagram and turbulent kinetic energy cloud diagram of each medium and low specific speed pump as a turbine,it can be seen that whether the medium specific speed or low specific speed pump is used as a turbine,as the cutting rate increases,the impeller inlet The larger the return flow is,the greater the loss between the volute and the impeller gap.The subject also obtained the cutting law of the turbine turbine with the intermediate specific speed based on the assumption of the Euler formula and the inlet and outlet speed triangle of the turbine impeller.The inlet and outlet speed triangle of the impeller is based on the assumption that the inlet angle and inlet width of the impeller are unchanged before and after the impeller is cut.1.For a medium specific speed pump as a turbine,when the cutting rate is between 3% and 9%,the error between the two is small,and when the cutting rate is12%,the error is large,indicating that the turbine impeller The cutting law can no longer be applied;in addition,when the cutting rate is 9%,the efficiency of each turbine decreases within 5%,so the maximum cutting rate of the turbine impeller is9%.For a low specific speed pump as a turbine,the cutting rate is between 3% and6%,and the error between the two is very small.When the cutting rate is 9%,the error is large,indicating that the maximum compliance with the turbine impeller cutting law The cutting rate is 6%.
Keywords/Search Tags:Centrifugal pump, Specific speed, Impeller cutting, Numerical simulation, Hydraulic loss
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