Numerical Simulation Study And Entropy Generation Character Analysis On The Process Of Stratification-rollover Of LNG Cargo Tank

With the increasingly close connection of global economy,the trade volume of natural gas is increasing year by year.As the main carrier of marine transportation of LNG,LNG carrier is favored by major shipping companies.However,the phenomenon of "rollover" may occur in the process of LNG transportation,which seriously threatens the safety of ships.Therefore,the problems of LNG stratification-rollover have been become a hot topic in the world.The process of LNG stratification-rollover was analyzed,and a two-dimensional physical and numerical model were established.The appropriate physical parameters of LNG was selected,and the static LNG tank and moving LNG tank were carried out stratification-rollover numerical simulation respectively.The influence of heat leakage intensity,initial layered height of liquid layer,moving amplitude and period on stratification-rollover of LNG were obtained.Based on the analysis of the distribution of entropy production and the change characteristics of entropy production,the influence mechanism of different factors on the stratification-rollover process of LNG tank was explored.The main conclusions are as follows:(1)The increase of heat leakage does not change the flow process of the boundary layer.Under the condition of single heat leakage intensity,the distribution area of flow entropy production changes with the heat leakage time,and increases with the heat leakage intensity.(2)When the LNG tank is in a static state,the time for complete mixing of liquid phase decreases with the increase of liquid stratification height;The entropy production value of fluid flow decreases with the increase of the liquid layer height;The entropy production value of fluid heat transfer decreases with the increase of liquid layer height.(3)When the LNG tank is in motion,the mixing rate of liquid density increases with the increase of motion intensity.The entropy production rate of liquid flow changes periodically,and it increases with the increase of tank motion intensity.The output value of heat transfer entropy decreases with the increase of motion amplitude,and it decreases with the decrease of motion period.