Research On Cavitation Flow Characteristics Of Cryogenic Butterfly Valve

Cryogenic butterfly valve is a kind of control parts used for regulating fluid flow state,control of opening and closing,mainly used for liquefied natural gas,liquid nitrogen,liquid oxygen,liquid hydrogen,ethylene and other cryogenic medium transmission process regulation,is widely used in energy,electric power,chemical industry,metallurgy,aerospace and other industries transmission system,in ensuring the stability and reliability of the system operation plays an important role.Cavitation is a phenomenon that often appears in the regulating process of cryogenic butterfly valve.The existence of this phenomenon will lead to the damage of key components during the operation,affect the use of equipment.And cause unnecessary losses.It is one of the important reasons for the failure of cryogenic butterfly valve and the instability of the system.In addition,the existence of cavitation often brings a lot of negative effects such as noise,mechanical vibration and so on.Therefore,exploring the influencing factors of cavitation in cryogenic butterfly valve is of important guiding significance for ensuring the stable operation of the system for a long time and developing butterfly valves with better performance.Aiming at the above problems,the main contents of this study are as follows:(1)Based on the thermodynamic effects in the process of cryogenic cavitation,the existing Z-wart cavitation model is modified,and a modified model suitable for numerical calculation of cryogenic cavitation flow field is proposed.The accuracy and applicability of the modified Z-wart cavitation model are verified by the results of numerical simulation and visualization experiments.The results show that compared with the original Z-wart cavitation model,the modified Z-wart cavitation model has a better ability to capture the pressure drop and temperature drop in the process of cryogenic cavitation.(2)The cryogenic cavitation flow field in butterfly valve under different opening degrees/operating temperatures was studied,and the influence of different opening degrees/operating temperatures on the cavitation flow field in the regulating process of cryogenic butterfly valve was analyzed.The results show that the cryogenic cavitation phenomenon is related to the distribution of low-pressure and high-speed regions in the flow field.The volume of cavitation and the influence of cavitation on the turbulence degree of cryogenic cavitation flow field basically increase with the increase of the opening degree.The spatial and temporal distribution of vortices in cavitation flow field is highly consistent with the evolution process of cavitation.(3)The cryogenic cavitation flow field in butterfly valve under different opening degrees/operating temperatures was studied.The entropy diagnosis method was used to quantify the irreversible loss in the cavitation process,and the total entropy production distribution cloud in the cavitation flow field and the entropy production distribution curve on the upper surface of the valve plate were obtained.The results show that the main distribution area of entropy production is the front wall of the valve,the upper surface of the valve plate and the flow field behind the valve.And the distribution area of entropy production fluctuates with the development of cavitation.The formation and movement of cavitation on the surface of the valve plate is the main reason for the formation and movement of the peak in the entropy production caused by the direct dissipation distribution curve(EPDD),and the change of cavitation volume is the main reason for the peak fluctuation in the curve.Compared with EPDD distribution curve,the influence of cavitation generation,development and collapse on entropy production by turbulence dissipation(EPTD)and entropy production by wall shear stress(EPWS)is significantly reduced.