Optimized Design Of Heat Transfer Enhancement Of LNG Intermediate Fluid Heat Exchanger

With the rapid development of China's economy and the adjustment of energy structure,liquefied natural gas(LNG)has become an important part of China's energy industry as a storage form of natural gas.LNG intermediate medium heat exchanger(IFV)is a relatively new type of gasifier,the heat transfer efficiency is high,can adapt to different quality of the sea,while a good solution to LNG gasification process of icing problems.However,IFV's advanced preparation technology is mainly controlled by foreign enterprises,and there is little research on the internal heat transfer and the design of heat transfer enhancement of such heat exchangers.In this paper,IFV is regarded as the research object and the heat transfer enhancement as the research goal,to build the mathematical model of the heat exchanger and further proposed heat transfer enhancement scheme.The flow and heat transfer mechanism of cryogenic LNG in round pipe and spiral flat tube were studied.It is found that the low temperature LNG produces a spiral flow in the spiral flat tube,which leads to the occurrence of longitudinal vortices in the tube and promotes the heat transfer enhancement process.When the Reynolds number is equal,the spiral flat tube has a maximum heat transfer factor Nu' of 1.50 compared to the round tube.The comprehensive evaluation factor ? is used to evaluate the performance of heat transfer and flow resistance of the spiral flat tube.The obtained ? is above 1.0,which shows that the integrated heat transfer performance of the spiral flat tube is good,especially in the excessive flow when the ? is up to 1.50.A one-dimensional calculation model of IFV was established to analyze the effect of fluid operating conditions on heat exchanger efficiency.The increase of inlet temperature,mass flow and LNG mass flow of seawater can improve the heat transfer capacity of IFV,while the change of LNG inlet pressure has little effect on that.The main thermal resistance of IFV is located in the propane side of the gasification zone and the NG side in the thermostat zone.The outlet temperature of seawater and natural gas and the saturated temperature of propane increase with the increase of inlet temperature and mass flow of seawater,but the saturated temperature of propane decreases with the increase of LNG mass flow and is not sensitive to the change of LNG inlet pressure.The increase in LNG inlet pressure has led to an increase in the natural gas outlet temperature and a slight increase in the outlet temperature of the seawater.The increase in LNG mass flow resulted in a decrease in seawater and natural gas outlet temperatures.The three heat transfer zones of the IFV should be subjected to different heat transfer intensities,and each enhanced mode has a different heat transfer factor.From the heat exchanger efficiency,economy and operational safety performance analysis to get the final enhanced heat transfer scheme for the evaporation zone using GEWA-T finned tube,gasification zone using spiral flat tube,thermostat zone sets baffle,while the tube arrangements are irregular.Compared with the original scheme,the scheme greatly reduces the volume of the heat exchanger,and the cost is reduced by 14.3%,which is helpful to the skid mounted design of IFV to meet the increasing demand of LNG gasification in China.