低速圧縮性流体の球環内流れ解析とLNG球形タンク断熱システムへの応用

概要

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Dynamic motions of low velocity compressible fluid in the annular space sided with two walls of ambient and low temperature was analyzed with two dimentional spherical coordinate system, where the forced convection and natural buoyancy driven flow co-exist due to the large variation of temperature. Physical properties especially for density varying with the temperature and pressure were incorporated in the differential equations, other properties, thermal conductivity and viscosity were replaced with the eddy viscosity which have a governing influence on the flow field. Turbulent analysis was based on the k-ε two-equation model. FDM discretization of MAC scheme was applied for the numerical analysis of compressible fluid. Solutions of steady state were obtained by the method of time marching integration of trasient state solutions. This theory of "vapor insulation" was applied to the spherical tank of LNG carrier as the new concept of insulation system. Cold nitrogen gas heat-exchanged with the boiled off LNG vapor was introduced into the annular space around the LNG tank, where the gas flows along the tank surface offsetting the heat gains from the hold space. Thermal inflow to the LNG cargo was diminished by this nitrogen gas heat absorption effect. In this paper the concept and configurations of the system are described.
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