Analysis of convection and boil-off in multi-scale membrane LNG tanks under sloshing excitations

The marine storage and transportation of liquefied natural gas (LNG) in membrane tanks involves complex thermodynamic responses, significantly affecting system operation reliability. The study investigates the coupled problem of heat transfer and sloshing in LNG tanks through small-scale experiments and simulations. A tank partially filled with R134a was analyzed under various non-isothermal sloshing excitations to examine the free surface, flow, and heat transfer. Changes in fluid temperature, wall temperature, and heat flux were measured under different sloshing frequencies, amplitudes, and filling levels. A Computational Fluid Dynamics (CFD) analysis was performed, considering heat flow in the insulation layer and phase changes in the membrane tank. The tank was assumed to be vented. A Volume-of-Fluid (VOF) model with a dynamic mesh provided insights into the effects of sloshing on heat transfer and flow. Model feasibility was confirmed by comparing simulation results with fluid sloshing experiments. An extended sloshing Nusselt number was calculated, and a correlation formula related to sloshing conditions was developed, allowing for a quantitative assessment of enhanced heat transfer. Simulations explored evaporation characteristics in various scales of LNG tanks under static and sloshing conditions. The results showed that the evaporation rate of LNG increases as the tank scale decreases, with sloshing significantly impacting LNG storage and transportation. The study enhances the understanding of heat transfer and flow evolution in LNG tanks, improving the accuracy of evaporation models and providing insights for optimizing tank design and operation under sloshing conditions.