Research And Development On The Automobile Air-Conditioning System For City Bus Applying The Liquefied Natural Gas

Liquefied Natural Gas(LNG),used as a vehicle fuel,can be vaporized into gas during its use and release a lot of cold energy.If this part of the cold energy can be recycled and use for the air conditioning system of the car,then it will save much more energy.The most critical equipment of cold energy recovery is heat exchanger.A large number of theoretical calculation and numerical simulation of heat exchanger are needed and the heat exchanger is optimize designed so that the heat transfer and energy saving effect can be ensured.Based on the research status of the cold energy recovery technology of LNG automobile at home and abroad,the spiral-tube heat exchanger is used as the key heat exchange element in the cold energy recovery system of LNG automobile.The heat transfer characteristics of different cross sections and different geometry structures of the spiral-tube heat exchanger are studied by numerical simulation.The research contents are as follows:Firstly,based on the platform advantage and theoretical foundation of software Fluent,the theoretical basis of the flow and heat exchanging process in the heat exchanger are elaborated in detail.A numerical simulation is carried out for the heat transfer experiment of liquid nitrogen and LNG in the reference literature.The numerical simulation results are in good agreement compared with the experimental results and the feasibility of the numerical calculation method is verified.Secondly,the different cross sections of spiral-pipe heat exchanger of LNG vehicle for cold energy recovery are simulated.The distribution of the corresponding pressure field and temperature field,and the heat transfer coefficients are obtained.The flow field characteristics and heat-exchange effect of the circular cross section of heat exchanger are well determined,which is the foundation for thestructure selection and numerical calculation of the spiral-pipe heat exchanger.Thirdly,the effect of heating fluid velocity on the fluid flow and heat transfer in the heat exchanger of the helical casing is calculated.The numerical calculation of spiral-pipe heat exchanger with different spiral diameter and spiral pitch is carried out,and the flow and heat transfer characteristics in the heat exchanger are obtained.This provided the theoretical basis for the optimal design of heat exchanger.In this paper,the basic structure of the cold energy recovery of spiral-pipe heat exchanger in LNG automobile is determined by the numerical simulation method,the numerical calculations of spiral-pipe heat exchanger from different structure forms are carried out and the characteristics of fluid flow and heat transfer in heat exchanger are obtained.This provides references for the optimization design of cold energy recovery spiral-pipe heat exchanger.