Design And Flow Analysis Of Inducer For LNG Pumps

Low temperature liquefaction effectively solves the problem of inconvenient transportation and storage of natural gas.In this process,LNG pump is the key tool for transporting medium.The cavitation of the cryogenic liquid greatly affects the stable operation of the unit,and the addition of inducer can effectively solve the problem.At the present stage,the design of inducer is more dependent on the experience of the designer,and the effect of thermodynamic effect on the performance of the design is neglected.Therefore,it is very important to reduce the dependence on the empirical parameters in the design process,to improve the controllability of the design process of the inducer and to discuss the influence of the thermodynamic effect on the performance of the inducer.In this paper,based on the original design method,a model of circulation distribution was presented to complete the hydraulic design of inducer combined with correlation studies on axial pumps.Through numerical simulation,the internal flow characteristics and cavitation characteristics are studied,and the influence of thermodynamic effect on pump performance is discussed by changing the transport medium.The main research contents and conclusions are as follows:1.Based on the basic equations of fluid motion and the radial equilibrium equation,the distribution model of the blade outlet circulation is established.Four different types distribution of circulation models are given,and the corresponding axial velocity distribution is derived to provide a theoretical basis for subsequent hydraulic design.2.Based on the thermodynamic Clapeyron-Clausius equation and combined with the heat transfer during the process of cavitation,the influence of thermodynamic parameters on inducer cavitation is deduced.In order to investigate the influence of thermodynamic effect on the inducer cavitation in inducer,the normal temperature water and low temperature LNG were used as working medium.3.Based on the original design method,the theory of nonlinear circulation distribution is introduced to control the angles of the inlet and outlet of the blade at different heights.At the same time,through the simultaneous transformation of equations and reduction of empirical parameter selection in design process,the preset parameter was converted into a verification parameter,and then completed the hydraulic design of inducer.4.Three dimensional modeling of the new designed inducer,prototype inducer,prototype pump impeller and volute was made by PRO/E,and it was assembled according to certain axial spacing and circumferential timing position.The steady numerical simulation is carried out by using ANSYS software with the normal temperature water as the transport medium.The results show that,compared with the prototype inducer,the static pressure gradient on the surface of the new inducer blade is more obvious.Circulation distribution has little influence on the lift of the pump,but has a certain influence on the efficiency of the pump.5.Numerical simulation of cavitation for two pumps was done with normal temperature water as medium.The results show that,the cavitation performance of the new pump is much higher than that of the prototype pump.Through the analysis of the volume fraction of the cavitation bubble on the blade surface after and before the cavitation,it is found that the main reason for the improvement of the cavitation performance of the pump is the surplus energy provided at the main impeller inlet.Through the analysis of the development law of the cavitation bubble distribution in the transition section from the exit of the inducer to the inlet of the main impeller,it is found that the pressure rise in the transition section can effectively restrain the further development of the cavitation caused by the inducer.6.Numerical simulation of cavitation for the new pump was done with LNG as medium instead of normal temperature water.The results show that,the thermodynamic effect has a certain inhibitory effect on the pump cavitation,but when the pump is designed to transport LNG on the basis of clear water,the cavitation performance of the pump deteriorated.