The Simulation Study On Liquid-hammer Phenomenon In Liquid Nitrogen Supply System

Cryogenic fluids,such as liquid nitrogen,are widely used in cryogenic liquid rockets,large-scale scientific facilities,large-scale air separation,hydrogen transportation,and etc.In the cryogenic liquid system,when there is a dramatic change in flow rate due to valve opening and closing,it will cause the phenomenon of liquid hammer.The macroscopic performance is that the internal pressure of fluid changes dramatically,which then exerts a great impact on the pipe wall of the supply system,resulting in the damage of flow passage components,the rupture of pipeline,the leakage of the cryogenic fluid,or even accidents.The phenomenon of liquid-hammer occurs widely in the supply system,whereas most of the existing liquid-hammer research results are based on water and water network system.Compared with the normal temperature fluid,liquid nitrogen and other low-temperature fluid has a great physical difference in volume elastic modulus,viscosity,density and other physical properties,and it is easy to vaporize to form two-phase flow.As a result,it is different from the liquid hammer phenomenon in the water pipe network system,and the applicability of the related conclusions of the liquid hammer in the water pipe network in cryogenic fluid is yet to be tested.Based on liquid nitrogen as the working medium,according to a typical liquid nitrogen supply system designed by China Aerodynamics Research and Development Center,the causes and influencing factors of liquid-hammer phenomenon in liquid nitrogen supply system are studied,and the suppression measures of the liquid-hammer phenomenon in cryogenic fluid supply system are discussed.This paper mainly carried out the following work:(1)The key components such as liquid nitrogen plunger pump,buffer tank,regulator valve and nozzle are modeled separately,and the overall model of the liquid nitrogen supply system is further constructed on the basis of it,and the simulation calculation under steady-state conditions is carried out.The simulation results are well consistent with the experimental results,and the accuracy of the model in steady state condition is verified.(2)In the view of the liquid-hammer phenomenon in a single tube,the simulation calculation and theoretical calculation are carried out.The simulation calculation results of liquid-hammer pressure,tube fundamental frequency and the second-order frequency agree well with the theoretical results,which confirms the feasibility of AMESim in liquid-hammer simulation,and lays a foundation for the simulation study of liquid-hammer phenomenon in the liquid nitrogen supply system.(3)Taking the liquid nitrogen supply system as the research object,the simulation study of liquid-hammer phenomenon is carried out,and the simulation results agree well with the experimental results.The effect of density,volume elasticity mode,viscosity and gas void fraction on the liquid-hammer phenomenon is analyzed,in which the peak of liquid-hammer pressure decreases with the decrease of density and volume elasticity mode,decreases with the increase of the viscosity and gas void fraction.(4)Aiming at the liquid-hammer phenomenon of the liquid nitrogen supply system,the corresponding suppression measures are studied,among which the extended time sequence of the valve closing duration,the adoption of the first fast and then slow timing,the reasonable arrangement of accumulator and bellows can inhibit the phenomenon of liquid-hammer to different degrees.