| There are two main ways of gas liquefied storage, namely high pressure storage (such as liquefied petrolum gas, LPG) and cryogenic storage (such as liquefied natural gas, LNG). If the storage tank of these liquefied gases expose to thermal environments, the rise of tank pressure, as well as the increase of the wall temperature and medium temperature will drive the tank to failure. Once failure, the tank rupture may also initiate the boiling liquid expanding vapor explosion (BLEVE). This kind of accident often happens in both domestic and foreign. Therefore, it is of practical significance to research the dynamic response of liquefied gas tanks in thermal environments for proposing safe operation strategy and accident prevention measures.Though the accident patterns are different for different liquefied gas tanks, from the physical point of view, they are all the results of the coupled heat and mass transfer among the thermal environment, the tank wall and the internal medium. The results in the literatures show that when the liquefied gas storage tank exposed to the external thermal environment, the medium in the tank was often thermal stratified and the stratified temperature response of the liquefied gas directly determined the energy storage in the tank and the pressure rising rate, further influenced the safety of the storage tank. In this thesis, the researches for this topic are conducted as followings:Firstly, the thermal response experiment of a liquefied gas storage tank was performed, and the typical pressure and temperature response of the tank were acquired. Experimental results show that the dynamic response of the tank presents various characteristics in different regions and stages. By analyzing the heat and mass transfer rules in the experiments, a physical model was proposed to describe the heat-mass coupling response process of the liquefied gas tank, which includes the coupled heat transfer among the thermal environment, the tank wall and the internal medium, as well as the coupled process of the heat transfer in the tank and the mass transfer inner the internal medium.Secondly, on the basis of the experimental study, a multi-zone and multi-phase numerical model was established to coupling solve the solid heat transfer in the tank wall and the heat and mass transfer between the liquid phase medium and gas phase medium. The model was verified by comparing with the experiment. Through numerical simulation, the hydrodynamics mechanism and heat-mass transfer mechanism of the tank response process were studied. Further, the temperature stratification evolution characteristic of the flow field and its effect on the heat transfer process was revealed. Results show that after the temperature stratification eliminates, the hear transfer near the wall changes from single phase convection heat transfer into boiling convection heat transfer.Thirdly, the effects of the gas filling condition and external heat environment on the tank pressure, medium temperature and the tank wall temperature were investigated. The results show that when the liquefied gas filling rate is low, the liquid surface temperature and the tank pressure rising rate increase faster, and the liquid stratification was more obvious. When the external thermal convection was strong, the wall temperature and the tank pressure increased faster. If the tank cracked, the medium superheat would be lower because of the higher degree of temperature stratification, as a result of which, the explosive boiling would be weaker. In lower engulfing degree case, the tank was very like to form firstly finite gap, then occurred secondary disruption due to explosive boiling. When the flame temperature was higher, the tank would fail faster, but the rupture pressure was relatively low.Finally, the evolution process of the stratification driven by the temperature and component differences was investigated, through adding component transport effect on the general heat-mass coupling response model of the liquefied gas tank. The results show that when the tank is side heated, boundary penetration is the main factor to cause rollover, and the interface migrates from up to down. When the tank is bottom heated, the interface presentes opposite migration relative to the side heated situation. When rollover occoured, if the heavy component content in the lower liquid was higher, the overpressure would be lower. |
