Study On Heat Transfer Of LNG Valve And Optimal Design Of Clearance Of Long Neck Valve Cover

LNG has the advantages of convenient transp ortation,storage and little pollution,so it is widely used in industrial production.A large number of control valves are required on the LNG transportation pipeline,which are collectively referred to as LNG valves.As a certain gap between the long neck valve cover and the valve stem of LNG valve,a small amount of LNG will enter the gap,and forced convection heat exchange and heat conduction will be carried out with the long neck valve cover and the valve stem,resulting in LNG cold loss.To solve the problem of cold loss in LNG valves,this paper takes 2 "300LB low-temperature ball valve as the research object and uses the numerical calculation method to mainly carry out the following researches:(1)In this paper,the development status of fluidized boiling heat transfer and cooling loss technology in micro channel is summarized,some methods to reduce cooling loss in low temperature valves are introduced,the special requirements of LNG valves are briefly described,and the change of flow pattern and convective heat transfer coefficient in the flow boiling process of vertical pipe and the heat transfer calculation model of two-phase flow are discussed.(2)Taking 2 "300LB low-temperature ball valve as the research object and adopting numerical simulation method,the geometric model of LNG valve's long neck bonnet and stem clearance was established.The cooling loss between LNG valve long neck cover and stem was studied,and the relationship between the convection heat transfer coefficient and flow pattern with time under different working conditions was analyzed and calculated,which provided support for the research on reducing the cooling loss in the gap of LNG valve.(3)With the inlet pressure,inlet temperature,heat flux,wall thickness and other factors of the gap between the long neck valve cover and the valve stem as variables,the change trend of the convection heat transfer coefficient when the gap between the valve cover is 1mm was studied by numerical simulation method.(4)Take the gap size between the long neck valve cover and the valve stem as a variable,and use Workbench software to analyze the cloud chart and curve chart of temperature change on the lower wall surface of heat transfer between different valve cover gaps.(5)Through the above research,the numerical calculation method used in this paper can provide a reference for the reduction of cold loss in the cover and stem of the cryogenic valve,and also provide data support for the determination of reasonable clearance size between the cover and stem.