The Research On Variation Law Of Pressure In Cryogenic Vessel

In the last half of the 20th century, the cryogenic technology was expanding by leaps and bounds. With the popularity of cryogenic technology, cryogenic liquids such as liquid nitrogen, liquid oxygen and liquid argon, liquid hydrogen and liquid helium, liquefied natural gas, were applied in wide range day by day, furthermore the demand of the storage and transportation of cryogenic liquid was increasing continuously. Because of the cryogenic liquids with the characters of low boiling point, small latent heat of vaporization and high-cost to refine, it is of the utmost economic value to storage and transport cryogenic liquid safely and effectively. So it has very important value to research the non-loss storage and transportation of cryogenic liquids. In this paper, a 15L high vacuum multi-layer insulation cryogenic vessel was selected to do the research on the change of pressure in the cryogenic vessel filled with liquid nitrogen.Firstly, the thermodynamic and migration nature of liquid nitrogen were analyzed, and the saturation vapor pressure, density, specific heat and specific enthalpy of nitrogen were calculated with the appropriate formulas, which played a key role on the accuracy of thermodynamic calculation.Then, the theory of heat transfer of high vacuum multi-layer insulation cryogenic vessel was analyzed, and the formulas for the heat leakage calculation of each part of the vessel were listed out. After a comparative analysis of the cryogenic liquid thermodynamic models established by predecessors, it adopted the three districts model to research the pressure changes in the cryogenic vessel, and programmed for calculating the law of pressure changes. The results show that the ambient temperature and the effective heat transfer coefficient of thermal insulation layer are the important factors that affect pressure changes in the cryogenic vessel. With a certain initial filling rate, the pressure in the vessel increased gradually with the passage of time, and in the later period the speed of pressure increasing became faster. The more the heat leaked from thermal insulation layer of vessel, the faster the pressure rose.The author did many times of non-loss storage and transportation experiments to the cryogenic liquid with different initial filling rate. The experimental results show that initial filling rate of cryogenic liquid is one of the important factors that affect the pressure changes. Comparing the calculation data with the experiment results, the both are consistant. The research indicated that the change of heat state parameters with the pressure increasing can be predicted accurately by programming calculation.