Calculation of Boil-Off Rate of Liquefied Natural Gas in Mark III tanks of ship carriers by numerical analysis

The heat flow from environment to LNG stored in Mark III of ship carriers is calculated in this paper by numerical simulations. Four different approaches are defined and evaluated: Approach 1 starts from simple 2D numerical computations of heat fluxes over representative sections of the insulation barriers in 10 specific temperature configurations defined by published data. Approach 2 evolves toward full 3D simulations of insulations layers under the same temperature configurations. A Reduced Order Model is next developed by calculating equivalent thermal conductivity for insulation barriers. This equivalent thermal conductivity is applied in the fluid flow and heat transfer simulation from the environment to the LNG in 2D and 3D models by Approaches 3 and 4, respectively. For a full ship with a capacity of 165,000 m3 with 270 mm thick insulation barriers, the obtained BOR and the overall heat transfer coefficient vary from 0.895% and 0.0656 W/m2⋅°C for Approach 2 to 0.0945% and 0.0693 W/m2⋅°C for Approach 3. For Approach 4, the BOR and overall heat transfer coefficient are 0.0919% and 0.0674 W/m2⋅°C. When the thickness of the insulation barrier is increased to 400 mm, these initial values are reduced to 0.0631% and 0.0453 W/m2⋅°C.