Research On Influencing Of Reflux Hole On Hydraulic Performance And Self-priming Performance Of Vertical Self-priming Pump

Self-priming pump as a special centrifugal pump,its performance includes self-priming performance and hydraulic performance.The position and area of reflux hole have important influence on the internal flow and performance of pump,but the research on it is still not thorough.This paper will be a kind of vertical self-priming pump as the research object,through theoretical analysis,numerical calculation（involving the CFD unsteady numerical calculation with the unsteady gas-liquid two-phase flow numerical calculation）and com bined analysis of test method,and the two factors of reflux hole design different solution（position and area）,in this paper,the research on the influence of vertical self-priming pump performance.As follows:1.In the normal working stage of the verti cal self-priming pump,the influence of the position and area of the reflux hole on its hydraulic performanceA reflux hole was set on the side of the volute,and 10 and 15 groups of schemes were designed for the area and position of the reflux hole respectively.One scheme was selected as the model scheme for experimental measurement,and then the effectiveness of the numerical calculation method was verified by comparing the experimental results with the numerical calculation results,and the error was within the allowable range.Then,steady numerical simulation was carried out for each design scheme.The results show that the influence of different positions of reflux hole on the head of vertical self-priming pump is less than 5.3%and the influence on efficiency is less than 2.1%.The influence of different areas of reflux hole on head is less than 3.4%,and the influence on efficiency is less than 2.8%.The reasons are as follows:Vertical self-priming pump hydraulic performance mainly embodied in the normal working stage,and the flow in the gas-liquid separation chamber and the flow of the volute inside after imbibition stage to complete a clear boundaries,and reflux hole in different position is the main influence of flow of gas-liquid separation chamber,that is to say,the reflux hole on both sides of the volute and despite the energy transfer between gas and liquid separation chamber.However,the mutual interference to the flow is very small,and with the increase of the reflux hole area,the volute structure is more incomplete,but the existence of gas-liquid separation chamber just compensates for the missing structure of the volute,and makes up for the flow instability caused by the volute structure.Therefore,for the vertical self-priming pump as a whole,in the normal working stage of the vertical self-priming pump,the change of reflux hole position and area has little influence on its hydraulic performance.2.Influence of reflux hole area on self-priming performance of vertical self-priming pumpIn order to study the influence of reflux hole area on the self-priming performance of vertical self-priming pump,this paper designed S₁’-S₈’total 8 groups of reflux hole area scheme to carry out unsteady numerical calculation of gas-liquid two-phase flow respectively,and found that:1)The change of reflux hole area mainly affects the self-priming time of vertical self-priming pump:a.The smaller the reflux hole area is,the shorter the self-priming time is.b.The self-priming time is basically unchanged with the increase of the area of the reflux hole,but 1 3%longer than the minimum self-priming time obtained in the empirical formula.c.When the area of reflux hole exceeds the interval in b,the self-priming time will be significantly prolonged.2)The area of reflux hole also affects the mixing degree of gas-liquid two phases in the self-priming process of vertical self-priming pump:except for the optimal area,the mixing degree will be high first and then low with the increase of the area of reflux hole;But at the same time because the gas is limited,so the mixing degree will ha ve a saturation value,beyond this saturation value,the area of the reflux hole will increase on the self-priming performance not only did not improve,but because the redundant structure of the original flow in the vertical self-priming pump,the reflux hole will have a reaction,so that the self-priming time will be longer.3.Influence of reflux hole position on self-priming performance of vertical self-priming pumpIn order to study the reflux hole position on the influence of vertical self-priming pump self-priming performance,the thesis through the designφ₁’-φ₈’total 8 groups of reflux hole position scheme respectively on the gas liquid two phase flow unsteady numerical calculation,the study found that:1)Influence on self-priming time:under the same reflux hole area,different reflux hole position,vertical self-priming pump exhaust completion time will be different;The closer the reflux hole is to the tongue and volute outlet,the longer the self-priming time is,that is,there is an optimal range for the reflux hole.The self-priming time obtained from the design of the reflux hole position scheme can be concluded that the best opening position of the reflux hole inφ’=140°,the best range of the reflux hole position isφ’=60°～220°,within this range,the maximum difference of the self-priming time of the vertical self-priming pump is5.4%,And the reflux hole position close to the exit than close to the tongue vertical self-priming pump self-priming longer.2)By comparing the position of vortex generation,it is found that:the closer the reflux hole is to the volute tongue position and the volute outlet position,the closer the reflux hole is to the positions on both sides of the gas-liquid separation chamber,the smaller the allowable degree of objective structural conditions for vortex generati on;The closer the reflux hole is to the axial section of the volute and the gas-liquid separation chamber,the more symmetrical the vortex distribution tends to be.3)In the process of self-priming,the gas-liquid mixing degree of the vertical self-priming pump will be affected by the location of the reflux hole,but the gas-liquid mixing degree has no direct influence on the self-priming time of the vertical self-priming pump in the self-priming stage.4.Based on the gas and liquid two-phase unsteady numerical simulation also found:vertical self-priming pump gas liquid two phase mixture mainly in imbibition in early stage,middle gas mainly exist in the gas-liquid separation chamber and the outlet pipe structure,such as basic no gas in the impeller,it also makes the basic began to lift into the stable phase,namely the effect of reflux hole has been basically completed.That is,in the middle and late stage of the vertical self-priming pump to complete the self-priming stage and enter the normal workin g stage,the reflux hole does not play a role and have a little effect on the performance of the vertical self-priming pump.