Foundamental Research on the Tank Insulation System by Means of Cold Vapor Evaporated from the Cryogenic Liquefied Gas Cargo

(1)为评价蒸汽保温系统，制备了由高温空间、低温空间和低温蒸汽流动空间组成的保温箱。通过化学冷却剂将低温源控制在10 ~ 10℃左右，通过电加热器将高温空间保持在50℃左右。两个空间的温度分布通过每个空间提供的搅拌风扇保持在均匀的水平。低温蒸汽由-78℃的固体CO_2升华气体产生。(2)在没有蒸汽保温系统的情况下，计算得到热空间直接向冷空间的热流。通过对几种不同汽流量的实测温度进行实验和计算，得到了蒸汽保温系统应用后的有限热流。通过对两种热流值的比较，得出结论：在两个空间之间应用蒸汽流可使隔热效果提高约70 - 80%。(3)在此基础上，对直径分别为40m和30m的LNG和LH_2储罐进行了应用研究。该系统的结构是将液化天然气或LH_2蒸汽蒸发后冷却的低温气体N_2引入球形罐的底部和环空的赤道区，以避免罐周围的危险气体。利用能量方程和Navier-Stokes方程对可压缩气体的热流和汽流进行了分析。数值计算结果表明，在整个球面积上保温效果提高了20 ~ 30%，在单层的情况下，由于剩余的低温未被利用，LH_2储罐可能有多层的蒸汽流动空间。

(1) For the evaluation of the vapor insulation system insulation box which consists of a high temperature space, low temperature space and low temperature vapor flow space was prepared. A source of low temperature was controlled at about 10 to 10℃ by means of a chemical coolant and high temperature space was maintained a about 50℃ by an electric heater. Temperature distributions of both spaces were maintained at an even level by stirring fans provided in each space. Low temperature vapor was produced from the sublimated gas of solid CO_2 of -78℃.(2) Direct heat flow from the hot space to cold space without vapor insulation system was obtained by the calculation. Limited heat flow after an application of the vapor insulation system was obtained through experiments and calculations of measured temperatures of a few different quantities of vapor flow. After comparison of both heat flow values it was concluded that an insulation effect was enhanced by about 70 to 80% by application of vapor flow in between both spaces.(3) Applications to an actual tank of LNG and LH_2 whose diameter was about 40m and 30m were studied on the bases of above result. Configuration of the system is that low temperature gaseous N_2 which was cooled by an evaporated LNG or LH_2 vapor is introduced into the bottom point and the equatorial area of annular space of spherical tank in order to avoid the dangerous gas around the tank. analyses of heat flow and vapor flow by energy equation and Navier-Stokes equations for compressible gas were carried out. Numerical results showed that insulation effects increased by about 20 to 30% for the whole spherical area and multi layers of vapor flow space might be possible for LH_2 tank because of unused low temperature remained in case of single layer.