Heat Transfer Simulation In Cryogenic Test Of Cryogenic Valves And Development Of A Test System For Cryogenic Treatment

Cryogenic systems have been widely applied in modern industries in recent decades. At low temperatures, change of material structure may occur, e.g., the transition of stainless steel crystal from austentite to martentite, accompanied by the change of property (including size dimension). To avoid the negative influence due to the property instability, the aforehand cryogenic treatment of structural material is required. Besides, tests at low temperatures are also usually needed to examine the sealness and mechanical properties of cryogenic valve products before puting them into use.Experiential equations and researched results have been reviewed to propose the convection heat transfer coefficient of valve material, which is immersed into liquid nitrogen. Based on this, experiments have also been conducted to obtain the cooling-down curves of a stainless steel disc, which are then compared with the simulation result to modify the convection heat transfer coefficientThe modified convection heat transfer coefficients are used to simulate the cryogenic valve's dynamic heat transfer process, in order to guide the cryogenic treatment and product test. To solve the problem of icing on packing, a scheme of adding insulation material at the shaft position is proposed. Simulation is then carried out to check the effect of the addition of insulation layer.An experimental apparatus, with controllable operating temperature, has been built up for cryogenic treatment of different cryogenic engineering material. The platform is expected to support our further study on the mechanism of cryogenic treatment.Finally, the "inverse" heat transfer method is adopted to analyze the heat transfer coefficient through some relatively simple experimental measurement of temperature distribution inside a stainless steel plate. The preliminary work in this aspect shows the feasibility of this method, and also demonstrates the difficulties to realize it, especially the sensitivity with temperature measurement accuracy. More efforts should be devoted on this, and it will be helpful for accurate simulation of the dynamic heat transfer process.