Study On The Internal Energy Loss Mechanism Of Double Suction Centrifugal Pump Under Forward And Reverse Conditions

Currently,driven by the development goals of "carbon peak" and "carbon neutrality",China is accelerating the promotion of energy revolution,adjusting energy structure,optimizing resource allocation,and increasing rese arch efforts on energy-saving technology and equipment,with the aim of completing the transformation of the energy industry from resource dominance to technology dominance as soon as possible.Double suction centrifugal pumps play an important role in the process industry with high flow and high head when running forward,and can recover the rich liquid pressure energy in industrial systems during reverse operation.which has great practical significance for the construction of a clean,low carbon,safe and efficient energy system in China.However,in practice,the hydraulic performance and safety of the double suction centrifugal pump are greatly challenged due to the frequent occurrence of unstable flow phenomena such as internal flow separation,vortex and reflux under forward and reverse conditions.Therefore,this paper analyzes the law of internal energy loss and energy dissipation mechanism of double suction centrifugal pumps under both forward and reverse operating conditions using the entropy production theory,through a combination of numerical simulation and experimental methods,and systematically compares the energy loss of double suction centrifugal pumps and double-suction centrifugal pump as turbines(referred to as "double-suction pump as PAT").This provides theoretical basis and reference for subsequent selection and matching,optimized design,and safe operation.The main research contents and results of this paper are as follows:At different flow rate conditions,wall entropy production loss and turbulence entropy production loss are the dominant factors in the entropy production loss of the double suction pump,accounting for an average proportion of 51.20% and 45.40% in the total entropy production,respectively.Direct entropy production has a very low proportion of only 3.40%.The entropy production loss of each flow component is ranked from large to small are volute,impeller,and suction chamber,accounting for an average proportion of 52.00%,45.00%,and 3.00%,respectively.The volute and impeller are the main components that produce energy loss in the double suction pump.The local entropy production rate of the volute is mainly caused by the flow separation from the fifth section to the eighth section in the main flow area under s mall flow conditions and the unstable flow in the volute diffusion tube under large flow conditions.The local entropy production rate of the impeller is mainly caused by the strong dynamic and static interaction between the inlet and outlet of the impeller,the flow separation on the suction side of the impeller blade,jet-wake phenomenon at the blade trailing edge on the blade,and the reaction effect of bad flow in the volute.During the operation of the double suction pump as PAT,wall entropy production loss and turbulence entropy production loss are the dominant factors in the total entropy production,accounting for an average proportion of 5 4.67%and 41.00%,respectively.Direct entropy production loss has a very low proportion of only 4.33%.The entropy production loss of each flow component is ranked from large to small are impeller,draft chamber,and volute,accounting for an average proportion of 55.00%,29.83%,and 15.17%,respectively.The impeller and draft chamber are the main components that cause energy loss in the double suction pump as PAT.The local entropy production rate of the impeller is mainly caused by the flow separation and vortex generated at the suction side and pressure side of the blade,the dynamic and static interference between the volute tongue and the impeller,the bending flow with strong curvature between some impeller flow channels,and the reaction of the backwater zone of the draft chamber,The high local entropy production rate in the draft chamber region is mainly caused by special structure on both sides of the nose end of dead zones,the flow separation above the shunt baffle,and the unstable flow on both sides of the shunt baffle.Wall entropy production loss and turbulence entropy production loss are the two most important types of energy losses in double-suction pumps and double suction pump as PAT,with an average proportion of over 40% in the overall entropy production loss,while the proportion of direct entropy production loss is extremely low,only maintaining at around 4%,indicating that the wall effects in the near-wall region and unstable flow in the main flow region are the main causes of energy losses.The same distribution area of entropy production rates in each flow component of double suction pump and double suction PAT is concentrated in the downstream flow passage components and impellers.Among them,the effect of the suction chamber shunt baffle under pump conditions is benign,playing a role in diverting and optimizing internal flow,while the effect of the draft chamber flow divider under turbine conditions is malignant,exacerbating energy losses.