Dynamic modelling of the thermal response enhanced by sloshing in marine LNG fuel tanks

Abstract

This paper investigates the thermal response in marine liquefied natural gas (LNG) fuel tanks by experiments and modelling. The aim of this work is to develop phenomenological models that can predict the rapid pressure loss experienced onboard LNG fuelled vessels. Experiments have been conducted using water. A horizontally aligned tank made of steel has the same geometry as a LNG fuel tank, but at model scale. The tests are performed by supplying heat to evaporate water that is led through a closed loop from the bottom to the top passing a heating element. A lumped dynamic model is developed that can be tuned by adjusting few parameters. Uniform conditions are assumed in each phase. The model can provide useful insight and be combined with other submodels to perform system simulations. Good correspondence with the experimental data is found after tuning heat transfer coefficients, air content in the gas and the average temperatures. After validating the model, it is used to predict the necessary heat supplied to the pressure build-up unit (PBU) to maintain the tank pressure. A simple relation between the measured pressure and the PBU heat capacity is presented.