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

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(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.