Study On Dynamic Thermal Characteristics Of AAV Longitudinal Finned Tube With Integrated Cold Energy Thermoelectric Device

As the environmental problems become increasingly serious,liquefied natural gas(LNG)is of great significance to ease energy crisis and optimize global energy structure.The ambient air vaporizer has advantages of energy consumption,simple structure and low price,which is widely used in LNG vaporization peak regulating station.However,the traditional ambient air vaporizer not only wastes a lot of cold energy of LNG,but also causes frosting on the surface of finned tube,which reduces its heat transfer efficiency in the process.In this paper,we do investigation to the traditional ambient air vaporizer(AAV)and the ambient air vaporizer of the integrated cold energy thermal power generation device.Based on the conservation of mass and energy equation,the thermal dynamic model of the longitudinal fin tube of the traditional ambient air vaporizer and the integrated cold energy thermal power generation device is established.The model is discretized by the micro element method and programmed by Fortran The heat transfer characteristics of the longitudinal finned tube of the ambient air vaporizer under the subcritical pressure and supercritical pressure are simulated respectively.The distribution curves of the outside wall temperature of the finned tube,the temperature of the fluid in the tube,the thickness of the frost layer,and the convective heat transfer coefficient inside and outside the tube along the tube length are obtained.The influence of the structure parameters and the operation parameters on the heat transfer performance of the finned tube is analyzed.The results show operation pressure,air temperature and air humidity have significant influence on the frosting outside the longitudinal fin tube of the vaporizer,the LNG outlet temperature and gasification efficiency.The higher the operating pressure and air temperature,the thinner the frost layer,the higher the temperature of the LNG outlet,the greater the air humidity,the smaller the thermal resistance of the frost layer,and the higher the temperature of the LNG outlet;the change in mass flow rate has little effect on the thickness of the frost layer,but has great influence on outlet temperature of LNG,the smaller the mass flow rate,the higher the outlet temperature of LNG;Changing the fin height and the number of fins can also significantly enhance the heat transfer performance of the vaporizer.Secondly,the heat transfer characteristics of the longitudinal finned tube of the ambient air vaporizer with integrated cold energy thermoelectric power generation device are simulated,and the differences between the original finned tube and the new type finned tube are compared and analyzed.The curves of the generation density and the generation efficiency along the tube length under frosting and no frosting conditions are obtained.The results show that the new type finned tube structure is obviously different from the original finned tube structure under non frosting conditions,the difference between them is not significant in frost condition.Power generation efficiency of the new finned tube reaches 3%,power generation density reaches 50W/m.In the frost condition,power generation efficiency is only 1.48%,power generation density is 12.17W/m,and power generation in gas-liquid two-phase region accounts for the largest proportion of the total power generation,followed by single-phase gas region and single-phase liquid region.The results of this paper provide heoretical basis for the structural optimization of the longitudinal fin tube of the traditional ambient air vaporizer and new ideas for the utilization of LNG cold energy.