Numerical Simulation And Characteristics Optimization Of Water Jet Pump

As a kind of fluid equipment and water admixing device,water-jet pump can deliver energy and mass without mechanical energy by turbulent diffusion of fluidic,which is widely used in heating system.Using the differential pressure from heat network,it can pump and supply hot water with certain pressure and temperature for users.It has advantages of simple structure,easy installation and efficient in energy saving.However,the traditional design method of water-jet pump contains semi-empirical formulas,which will bring random design to the structure.As we all know,the drawback of water-jet pump is low hydraulic efficiency,and its internal turbulence flow is also complex.So the numerical simulation method is taken to optimize the structure size of water-jet pump in this paper.Firstly,according to the theory of E.?.???????,the characteristic equation of jet pump is deduced and the computing method of the structure is studied.Because the characteristic equation is complex,common solving method can not acquire the optimizing solution precisely and quickly,and the amount of computation of the structure size is huge.So,visual calculation is produced in this paper by using MATLAB software.By inputting different heating system parameters,the special parameter and structure size can be obtained directly,which can bring convenience to practical engineering design.For Characteristic equation introduction of the dimensionless characteristic curve,analyzed the relationship between cross-section ratio,head ratio and flow ratio under different operating conditions.From the angle of the heating engineering,put forward a kind of clearer and easiercharacteristic curve,q-(35)P_p curve andq-(35)P_g curve,for the designer and user.Aim at the actual heating system problem,given the reasonable operating differential pressure range by using theq-(35)P_p/?curve.It provides the basis for the district heating network regulation.After mastering the characteristics of water-jet pump,the structure size is optimized by using CFD method.The flow field in water-jet pump models with same cross-section ratio,different lengths of mixing chamber,different diffuser angles and different distances between nozzle and mixing tubeare simulated by using the K-?turbulence model and the SIMPLEC algorithm in the FLUENT software.Through the numerical calculation of flow field in different models,distribution curves of pressure,velocity and turbulent kinetic energy are acquired under same operating condition,andcharacteristic curves are acquired under different operating conditions.The study of mixing tube show that too short tube cannot make two fluids mixing well,which led to extra mixing loss of energy;andoverlong tube will increase the linear loss of mixed fluid.The study of diffuser angle show that too small diffuser angle will increase linear loss of mixed fluid and manufacturing cost;and too much diffuser angle may cause separation of the fluid and tube wall,which led to diffusion loss of energy.The study of the distance between nozzle and mixing tube show that too large distance may reduce the performance of water-jet pump and increase the mixing loss of energy because of tow fluids mixing untimely;and too short distance will cause cavitation of water-jet pump.