멤브레인형 LNG 화물창의 단열재에서 직사각형 밀폐공간 내에 자연대류 열전달에 관한 수치적 연구
Numerical study on natural convection heat transfer inside rectangular enclosures in the insulation of a membrane-type LNG cargo containment system
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초록
멤브레인형 LNG 화물창의 외벽에서 발생될 수 있는 결빙 현상을 이해하기 위해서, 단열재 내부에 냉온의 직사각형 밀폐공간 내에 자연대류 열전달과 상대습도의 상관관계를 대와동 모사를 이용하여 조사하였다. 등온 및 단열의 경계조건으로 단순화된 모델에서, 준-정상상태에 도달하였을 때에 대류열전달계수는 초기의 정지된 기체에 대한 것보다 약 2.5배까지 증가되었다. 대류열전달 특성에 대한 회귀분석의 결과를 바탕으로, 주어진 온도차에 의한 자연대류는 등온벽면 부근에서 우세하였지만, 유속의 크기에 따른 강제대류는 단열벽면 부근에서 더 우세하게 나타났다. 자연대류에 의한 열 및 유체의 유동에 따라, 가스온도가 이슬점 온도 아래로 떨어지는 경향은 LNG측 벽면 부근에서 대류열전달계수와 열유속이 상대적으로 낮은 지역에서 선호적으로 발생되는 것으로 확인되었다.
Abstract
To understand the icing phenomenon that may occur in the outer wall of a membrane-type LNG cargo containment system, the correlation between the natural convection heat transfer and relative humidity inside rectangular enclosures in the insulation was investigated by conducting a large eddy simulation. In simplified models with isothermal and adiabatic boundary conditions, the convective heat transfer coefficient was elevated to more than 2.5 times that of the initially stationary gas when the quasi-steady state was reached. Based on the results of a regression analysis of convective heat transfer characteristics, the natural convection owing to the given temperature difference prevailed in the vicinity of the isothermal wall surface. However, the forced convection as a function of the magnitude of flow velocity was dominant near the insulating wall surface. The results revealed that the tendency of the gas temperature to fall below the dew point temperature was preferentially generated in the region where the convective heat transfer coefficient and heat flux were relatively low near the LNG-side wall surface depending on the thermal and fluid flows as derived from the natural convection.
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