The Mechanism Study Of Effects Of Diffuser’s Diffusion On Nuclear Main Pump’s Performance And Internal Flow Characteristics

Nuclear power has become increasingly prominent in industrial production and human life, nuclear main pump has significant influence on the safety and efficient operation of reactor. In order to improve nuclear main pump’s hydraulic performance,provide effective reference for innovation design of nuclear main pump, in this paper took a centrifugal nuclear pump which specific speed is 157.8 as study object, the main research contents and results are as follow:1. The study on area ratio’s effects between impeller and diffuser on nuclear main pump’s performance.Cooperative relationships between flow components and their structural parameters are complicated, thus based on area ratio theory deduced the coupling relationship between diffuser inlet parameters and impeller outlet parameters, use area ratio to unify numerous parameters of impeller outlet and diffuser inlet, analyze this dimensionless parameter’s effect on nuclear main pump’s performance.Maintain impeller structure and alter diffuser inlet parameters to change the value of area ratio, according to area ratio equation chose diffuser entry width, diffuser inlet setting angle and number of diffuser blades as area ratio’s controlling factors.Combined with numerical simulation result and engineering experience, selected proper levels for each factor. Through numerical simulations and orthogonal experiments got the optimal area ratio value and pump head and efficiency variation curves with area ratio under rated flow condition. Chose three representative values according to the variation curves to study different the influencing mechanism of area ratio on nuclear main pump’s performance under different flow conditions.In the process of the research found that when ξ=0.645 the whole performance of the nuclear main pump is the best; during the increasing process of flow rate from0.8Qd to 1.2Qd, pump energy loss increased, its concentrated upon the diffuser throat;when ξ=0.797 the impeller’s power capability and the diffuser’s pressure recovery ability are better, when ξ=0.645 the loss within the diffuser is small, the control effect on fluid is strong, but the diffuser’s pressure recovery ability is poor under 1.2Qd flow condition; only depend on improving one hydraulic part’s performance is far from enough to improve nuclear main pump’s whole performance, improvements of cooperative relationships between hydraulic parts are more important.2. The study on of diffuser diffusion effects on nuclear main pump’sperformance.Found the optimal area ratio between impeller and diffuser is not enough to get the best result of diffuser’s improvement, still need to adjust diffuser outlet parameters.Thus defined diffusion calculation formula of diffuser, use this dimensionless parameter to represent synergistic relationships between diffuser outlet structure parameters, and analyze diffusion’s effect on nuclear main pump’s performance.Through alerting diffuser outlet parameters changing diffusion value, according to diffusion equation selected diffuser outlet width, diffuser outlet setting angle and diffuser blade outlet thick as controlling factors, Combined with numerical simulation results chose proper level values for each factor, took advantage of orthogonal tests and replace experiments with numerical simulations got the optimal diffusion value and nuclear main pump’s head and efficiency variation curves with diffusion values under rated flow condition. Chose three typical diffusion to study its influencing mechanism on nuclear main pump’s performance under different flow conditions.The results found that when KD=0.025 the pump whole performance is the best;during the increasing process of flow rate from 0.8Qd to 1.2Qd, diffuser loss and pressure recovery coefficient increased, nonuniformity of pressure and velocity curves increased; when KD=0 diffuser control action on fluid is stronger, pressure recovery ability enhanced, and local diffusion of diffuser throat is large led turbulence fluctuation become more serious, when KD=0.045 diffuser loss and pressure recovery coefficient are small; diffuser throat form has significant influence on diffuser’s performance, throat flow channel mainly induce the flow direction, get too much strong pressure recovery ability makes it hard for improving diffuser performance,should put reduce kinetic energy loss in the first place during the diffuser design process.