| With the global warming and frequent extreme climate disasters,stricter requirements are put forward for the performance of disaster rescue and relief equipment.Self-priming centrifugal pump,as the core equipment of flood control and emergency rescue,plays an important role in the fields of flood control.The traditional self-priming centrifugal pump has the disadvantages of low-flow rate,complex internal structure and poor self-priming performance.Moreover,the large flow centrifugal is difficult to start by self-priming,and the pump cavity needs to be filled with water before operation.The process is complex,greatly increasing the self-priming time,which unable to meet the requirements for rapid start in the emergency rescue conditions.Therefore,with the support of National Science and Technology program,a novel large flow and quick start self-priming centrifugal pump was proposed in this article.The design theory,entropy production loss,self-priming performance,and unsteady characteristics of the large flow and quick start self-priming centrifugal pump were systematically analyzed by the combination of theoretical analysis,numerical simulation,and experimental research.The investigation results have been applied in engineering practice.The main research contents and innovative results obtained are as follows:1.A novel large flow and quick start self-priming centrifugal pump structure was proposed.A jet entrainment system was innovative designed,which consist of first stage nozzle,second stage nozzle,connecting sleeve,and check valve.Through continuous delivery high-speed jets to the system,and subsequently continuous depressurizing through the two-stage self-priming nozzles,the air in the pump cavity was rapidly discharged,thus the large flow and quick start self-priming centrifugal pump could start under the condition of the pump cavity without water.At the same time,a drive clutch device was innovatively proposed to realize the synchronous operation of the air compressor and shaft during the self-priming process,and the rapid separation after the end of self-priming effectively reduced the energy loss during the operation of the pump.Finally,the self-priming mechanism of the large flow and quick start self-priming centrifugal pump at different stages during the start process was revealed.The test results showed that the flow rate of the pump is 500 m~3/h,head is 45 m and efficiency is 73%,and the self-priming time is only 62.5 s under the self-priming height of 5 m.The novel design of the pump not only improves the hydraulic performance,but also significantly shortens self-priming time.2.Transient numerical calculations of large flow and quick start self-priming centrifugal pump were carried out,and the influence of impeller meridian on unsteady characteristics of the internal flow field was analyzed.It shows that increasing the curvature of hub can not only effectively suppress the backflow in the flow field and improve the internal flow field,but also significantly increase the blades loading,which can obviously promote the function of blade.At the same time,as the increase of the hub curvature,the velocity distribution at the impeller trialing edge is more uniform.Meanwhile,the pressure pulsation amplitude and radial force at each flow condition are gradually reduced,and the hydraulic efficiency is significantly improved.Finally,measurement error and experimental verification were carried out,the deviation between the calculation result and the test result is less than 3%,which effectively improves the accuracy of the optimization design.3.The internal vortex structure and energy loss mechanism of large flow and quick start self-priming centrifugal pump with different blade thickness distributions were analyzed by employing vortex momentum transport equation and the theory of entropy production.The studies found that due to the different thickness distribution of the blades,boundary layer separation bubbles with different volumes and strengths were formed on the surface of the blade.Spatial structure of the vortex in the self-priming centrifugal pump was investigated based on Q criterion,and vortex can be divided into different types according to the three-dimensional structure and shape.Meanwhile,the intensity of the trailing edge vortex generated in the impeller is more disorder than other vortex and presents the distortion spatial structure.Therefore,vortex momentum transport equation is introduced to analyze the internal vortex formation mechanism.It is found that the viscidity diffusion variable plays a vital role in the separation of the boundary layer,which causes the generation of trailing edge vortex and destroys the stability of internal flow.At the same time,in order to accurately capture the size and distribution of internal energy loss in the large flow and quick start self-priming centrifugal pump,the entropy production theory is introduced to study the effect of blade thickness distribution on energy loss characteristics.It is found that employing the blade with increasement thickness distribution can not only significantly reduce the impact of incoming flow under over-load condition,but also decrease the boundary separation under part-load condition,which is benefit to improves the energy conversion rate of self-priming centrifugal pump under different flow conditions.4.By coupling the population balance equation model and Eulerian-Eulerian model,the model of bubble breaking and coalescence were loaded on numerical calculation,the law of gas-liquid two-phase flow under the coexistence of different size bubble condition was investigated,and the mechanism of the interaction between bubbles was effectively explained.It was found that the ability of bubble accumulation was enhanced due to the influence of the trailing edge vortex,and the distribution of large-sized bubbles upon the shroud is increasing,but the distribution is unevenly in the impeller flow channel,which caused the decentration of radial force.At the same time,as the gas voids increases,the collision frequency between the bubble groups is enhanced,and the internal flow stability of the two-phase flow is broken,thereby aggravating decentration of radial force.However,with the improvement of the flow conditions,the internal flow field is effectively improved,which has a significant promotion effect on reducing the pressure pulsation of the gas-liquid two-phase flow and the blade loading.5.The self-priming performance test rig with different altitudes were conducted,and the geometric parameters of the self-priming nozzle were optimized by experiments.Firstly,the relationship between the geometric parameters and self-priming time was obtained by combing the orthogonal test and gray correlation method.In order to verify whether there is an interaction between the parameters,the results are verified using a full-factor test method,and the effect of each parameter and the second-order interaction between the parameters on the self-priming time are analyzed.Based on all parameters and interactions,a self-priming performance model was established.In addition,the model was simplified by removing parameter variables and interactions that did not respond significantly to the self-priming time,and the simplified model error was reduced by 9.4%.The proposed model can effectively predict the self-priming time of self-priming nozzles with different geometric parameters,shorten the test analysis period,greatly reduce processing and production costs,and provide a reference for the optimization design of self-priming nozzles for the quick start self-priming centrifugal pump. |
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