Research On Pressure Rise Rate Of Cryogenic Vessels After Loss Of Vacuum

Impacts,pipeline leaks,and other factors may cause the insulation space vacuum of cryogenic vessels for submersibles to decrease,or even completely fail,causing its leakage heat to increase sharply,leading to a rapid rise in the pressure of the inner tank,posing a serious threat to the safety of the hull and personnel.Due to the special operating environment and task of the submersible,once the vacuum failure of the insulation space of the cryogenic vessels occurs,the submersible needs to be floated up to a dischargeable depth or water surface in order to relieve the gas in the cryogenic vessels and decrease the pressure of the inner tank.However,the pressure will continue to increase during the search for a place to allowable floating and the emergency ascent.Previous studies on the pressure rise rate of HVMIL?High Vacuum Multilayer Insulation?cryogenic vessels have mostly focused on the condition that the insulation space vacuum is intact or the insulation space vacuum has completely failed,and the research objects were mostly used in the aerospace and civil fields.There are rare studies on the pressure rise of cryogenic vessels for submersibles and their effects on submersibles under different degrees of insulation space vacuum failure.In view of the above problems,this paper studies insulation space vacuum failure with different degrees,the pressure rise of cryogenic vessels under different initial filling rate,and its impact on submersibles by the method of theoretical analysis,simulation and experimental research.The main research work is as follows:?1?A theoretical model is established between the insulation space vacuum of the HVMIL cryogenic vessels and the heat flux density passing through the inner tank wall.The model is used to calculate the heat flux density through the inner tank wall under different insulation space vacuum and the proportion of different heat leakage paths to the total heat leakage of the multilayer insulation.The average heat flux density through the inner tank wall increases as the insulation space vacuum decreases.When the insulation space vacuum is higher than 10^-2Pa or lower than 10Pa,the average heat flux density passing through the inner tank wall changes little with the decrease of insulation space vacuum.When the insulation space vacuum is between 10^-2Pa¹0Pa,the average heat flux density passing through the inner tank wall increases rapidly as the insulation space vacuum decreases.With the decrease of the insulation space vacuum,the proportion of residual gas heat conduction in the total heat leakage of the multilayer insulator increases and the proportion of radiant heat transfer and solid material thermal conduction to the total heat leakage of the multilayer insulator decreases.when the insulation space vacuum is lower than 10Pa,the residual gas heat conduction becomes the main way for the cryogenic vessels to leak heat.?2?A mixture model is used to simulate the evaporation of liquid nitrogen in a cryogenic vessel with a geometric volume of 110L at different insulation space vacuum failure and different initial filling rate.There is obvious temperature stratification in the cryogenic liquid in the cryogenic vessels.The pressure rise rate of the cryogenic vessels increases as the decrease of the insulation space vacuum or the increase of the different initial filling rate.At the same initial filling rate,when the insulation space vacuum completely fails?the insulation space vacuum is 10⁵Pa?,the maximum multiple of pressure rise rate of the cryogenic vessels is 10.4,4.93,and 1.36 times compared with the interlayer vacuum of 10^-3Pa,1Pa and 10Pa.At the same insulation space vacuum,the maximum multiple of pressure rise rate of the cryogenic vessels at the initial filling rate of 90%is 4.14 times and 2.46 times than that of the initial filling rate of 50%and 70%.?3?An experimental scheme is developed to study the effect of the insulation space vacuum failure degree and initial liquid level of the HVMIL cryogenic vessels on the pressure increase of the inner tank.An test-bed is set up to simulate the vacuum failure accident of HVMIL cryogenic vessels.The pressure rise rate of a cryogenic vessels with a geometric volume of 110L at an initial liquid level of 50%and a insulation space vacuum of 10^-3Pa is studied.The experimental results agree well with the corresponding simulation results?the maximum relative error is less than 3.5%?.?4?The influence of pressure rise rate on the treatment of vacuum failure accident of cryogenic vessels insulation space for submersible is discussed.The results show that the allowable time for handling the accident decreases with the increase of the pressure rise rate after the vacuum failure accident of the cryogenic vessels insulation space vacuum for submersibles occurs.Under the situation set in this paper,the allowable accident treatment time is 85min,50min and 26min when the pressure rise rate is 11.07kPa/min,14.58kPa/min and 25.67kPa/min respectively.