Research On The Heat Transfer Of LNG AAVS Under Frost Conditions

The natural gas industry of our country is in initial stage, and the demand for natural gas grow with each passing day. However, the energy structure of our country reflects the characteristics of "rich coal and less gas", which means that domestic production of natural gas is unable to meet the demand. As the crisis that the natural gas to our production cannot meet the demand, a large number of LNG imports from overseas. LNG gasified in the gasification station for users. The different types of LNG gasifier have advantages and disadvantages and conditions. The subject investigated in this thesis is AAVs, who has the simple operation, low cost and widely using. But due to frosting, the heat transfer is deteriorated. In this thesis, the heat transfer of LNG AAVs under frosting conditions are studied.By comparing the various frost crystal growth models and frost structure models existing, energy and mass conservation equations are established, choose the suitable correlation of the frost layer properties made the equations closed, then the equations are solved by the boundary and initial conditions, the correlation of each physical parameters in the frost layer varies with time in certain wall temperature and ambient air parameters are obtained when frosting, and the influence of various factors on frost resistance is analyzed.The mechanism of heat transfer of fin tube surface in air is analyzed, the appropriate calculation of correlations between air and the surface of the finned tube are selected to compute the heat transfer coefficient. The heat exchange efficiency and total heat transfer coefficient calculation of finned tube are calculated with frost layer adhering, then the factors affecting the air side heat transfer coefficient and the influence of various factors on the heat transfer coefficient are analyzed.The mechanisms of LNG boiling and gasification in the finned tube are analyzed, by comparing various correlations calculating the saturated boiling of pure substances, the calculation model applying to the gasification of LNG is selected where natural gas is regarded as a kind of pure virtual substances, and we obtained the heat exchange coefficient inside the fin tube.The dynamic processes of mutual coupling of the heat and mass transfer changes with time of LNG inside and outside the AAVS are calculated, the distributions of the internal and external parameters of finned tube in different time along the pipe are analyzed, the influences of different environmental parameters and structure parameters and operating parameters to the processes of the gasification are analyzed.