Research On Self-Priming Performance Impact Of Jet Centrifugal Pump With Designed Water Baffle

By virtue of its easy to use,reliable operation,self-priming and secondary start-up without water injection,the jet centrifugal pump is widespread used in agricultural irrigation.As the underground water level in parts of regions is declining due to river channel reconstruction and its over-exploitation.It is crucial to optimize the self-priming performance of jet centrifugal pump while guarantee its steady operation.In this paper,the jet centrifugal pump UJM75-2 with additional water baffle was taken as the research object.Based on the self-priming experimental investigation,and assisted with the gas-liquid two-phase fluid numerical simulation in the self-priming process.The purpose of this paper is to investigate the influence of the water baffle on the internal flow of the jet centrifugal pump chamber,and provide structural improvement suggestions for optimizing the pump cavity flow and self-priming performance.The main research contents are summarized as follows:(1)The jet centrifugal pump adds a water baffle with excurrent pores on the back of the deflector assembled the reinforcing rib.In this paper,six jet centrifugal pump improvement schemes were selected to conduct external characteristic tests and self-priming performance tests in proper sequence,including three assembly schemes of water baffle and deflector,three circumferential arrangement schemes of excurrent pores and pump outlet,and a scheme without water baffle.Comparing the test data found that the adding of the water baffle can cause the external characteristic curve to move down overall and the head break point moved forward.The new flow passage components increased the hydraulic loss inside the pump cavity.The comparison of the self-priming performance curve indicated that the adding water baffle exists an optimal riding position.The water baffle and the deflector were assembled through three uniformly distributed threaded holes,and there were three positional relationships between the non-uniformly distributed reinforcing ribs on the back side of the deflector and the excurrent pores on the water baffle.The three assembly schemes had less influence on the pump head,and the disturbance of the ribs on the back of the deflector caused the pump efficiency to decrease.During the self-priming process,the ribs below the excurrent holes accelerated the gas-liquid separation,and improve the gas-phase overcurrent capability of the pump chamber.The second scheme of the ribs below the excurrent pores closest to the outlet of the deflector has the bestIV self-priming performance,the self-priming height is 6.6m,and the self-priming time is 306 s.Theangles between the excurrent pores and the pump outlet were 0°,45°,and 90°.The 0° solution flushed the pump outlet,the maximum flow rate decreased,the pump efficiency decreased,while the angle was adjusted to 90°,and the flushing effect was weakened.The self-priming height is up to 8.5m,which is 2.3m higher than the assembly scheme of 0° angle,and the self-priming time is shortened to 204 s.(2)Single-phase numerical simulation of UJM75-2 jet centrifugal pump was carried out using commercial flow field analysis software CFX.The analysis found that the minimum static pressure inside the jet decreased with the increase of the operating conditions after the adding of water baffle.The break point of the head curve originated from the lowest static pressure point to induce liquid cavitation,so the head breaked in advance.The internal vorticity value of the jet decreased with the increase of operating conditions,and the internal flow line of the pump tended to be uniform.The flow of the impeller was analyzed by using the boundary vortex flux(BVF)flow separation criterion.It is determined that there is no flow separation among the inlet ring,the pressure surface and the suction surface of the blade under the design conditions,and the flow separation occurs at the hub edge of the impeller under low flow conditions.The axial vorticity of the pump chamber shows the 0° method to suppress the circumferential vortex of the scheme without the water baffle,but the axial vortex of the pump is increased due to the axial flushing action.The extreme value of the pump outlet vorticity reduces while the circumferential angle adjusts to 90°,the flow flushing is relieved,and the overcurrent capability of the pump chamber is improved.(3)The numerical simulation of gas-liquid two-phase flow in the self-priming process was carried out by using the double Euler multiphase flow model provided by CFX software.The results show that the ribs on the back of the deflector accelerate the gas-liquid separation to increase the gas volume fraction at the pump outlet.In the three assembly schemes,the scheme which the rib below the excurrent pores is the closest to the outlet of the deflector lead to maximum air volume fraction at the upper part of the pump chamber.In the three circumferential arrangement schemes,the air volume fraction of the same impeller is minimum while the angle is adjusted to 90°,the average gas flow rate is the largest,and the gas phase overcurrent capability of the impeller is optimal.That is,the gas phase accumulated in the impeller flowchannel preferentially enters the pump chamber without vortex.The gas phase flow capacity of the pump outlet is optimal.The gas phase in the scheme without adding water baffle pump chamber rotates with the liquid flow,keeping in the same direction with the impeller as the circumferential scouring the pump outlet,and the high-speed high-pressure fluid sprayed through the excurrent pore of the 0° scheme is scouring pump outlet axially,hindering the gas phase to eject from the pump body.The 90° scheme weakens the two scouring effects above,and the air volume fraction of the outlet straight pipe section is tendency to be uniform.Through the comparison of the transient values of the air volume fraction monitoring points in the pump chamber,it is found that the pump outlet value of the 90° scheme is maximum at the same time,and the gas phase overcurrent capability is as optimal as the test result.When adding the water baffle,the placement position should be adjusted to optimum location in order to improve the self-priming performance of the jet centrifugal pump.This modification has been applied to the company's products for the optimization of self-priming performance.