Loss Of Vacuum Experiment On A Multi-Layer Insulation Vessel

With the development of cryogenic insulation technology, Multi-Layer insulation has been widely applied in many industrial fields. However, for many cryogenic systems, the worst conceivable failure is a sudden, catastrophic loss of insulating vacuum. If the guard vacuum, which provides most of the insulation for the liquid is lost, the pressure of the vessel will rise rapidly. This in turn generates high pressure which must be relieved through some appropriate device. For some flammable and toxic gas, discharging the high pressure gas through the safety valves directly into environment may cause serious hazard to people and surrounding equipments. Recently, research of loss of vacuum insulation which was seldom involved in industrial insulated vessels is mainly focused on space technologies. Therefore, it's necessary to investigate the performance of industrial cryogenic vessels after losing vacuum insulation.In this paper, several experiments were carried out to investigate the thermal performance of the 175L thermal-insulated vessel after losing vacuum guard. These tests could be divided into two parts, one was mainly focused on the evaporation flow rate, while the other concerned the pressurization of the vessel. To find out the dependence of insulated material and heat flux, three types of insulation material combination were placed on the testing vessel. Taking into account of the changing of liquid-gas state, both temperature and pressure of the liquid-gas were investigated in these experiments. The result shows: the insulation material still performs some effort in thermal insulation after losing vacuum; during the pressurization period, the cryogenic liquid whose temperature is risen due to the sensible heat is subcooled, while the gas is always in superheated state; the working performance of safety valve can be summarized in three types, which are pressurization period, stable working period and unstable working period.Considering the heat transfer in the jacket when vacuum insulation was lost, model of heat transfer was established in this paper. Good results were received when applying this model in calculating heat flux and temperature distribution of the jacket of the vessel. In addition, numerical simulation was carried out to investigate phenomena of cryogenic liquid temperature stratification in the uninsulated tank. All efforts made in this paper were aim at the extreme condition of loss of vacuum insulation, the result of this paper can provide good suggestions in solving this kind of accidents.