Simulation And Optimization Of Automobile Air-Conditioning System And Comfort Study

At present,the research on air conditioning system and its thermal comfort is mostly based on the experimental methods.With the development of computer technology,simulation technology is more widely used owing to its various advantages.This paper,with a 9m passenger car as the research object,analyses the air conditioning systems and components,crew cabin flow and heat transfer using in the use of simulation technology,and propose a method for crew comfort evaluation.Based on the theory of air conditioning and refrigeration cycle,a one-dimensional simulation model is built on the basis of KULI software.The operating conditions are set according to the driving conditions.The simulation results are compared with the existing test values.The error is within the acceptable range,so the model can be used to simulate the operation of the vehicle air conditioning system.In air conditioning system,the heat transfer of the medium is carried out in the form of refrigerant phase change,while the microscopic flow state of the medium cannot be observed by the experimental method and the error between the simulation value and experimental value is great which can be solved by CFD methods.Based on the three-dimensional models of expansion valve and evaporator,the FLUENT software is used to simulate the three-dimensional phase transition process with the function of UDF,which is based on the basic equations of flow and heat transfer and select the RNG turbulence model and the Mixture multiphase flow model,set up thermodynamic relations of refrigerant R134a.Then the results of the three-dimensional calculation of the heat transfer coefficient are given to the one-dimensional model for amendment.The results show that the error between the simulated value and the test value is obviously reduced,and it proves that the one-dimensional model can be improved by three-dimensional simulation,which can greatly improve the accuracy of one-dimensional simulation and has great practical significance.On the basis of this,the one-dimensional model results are taken as boundary conditions,and the simulation software is used to analyze the flow field and temperature field of passenger cabin.In order to observe the influence of the flow field on the crew,dummy models are added to the model to simulate the passengers.The results of the initial simulation show that the outlet wind speed is too high,the body surface wind speed is high,while the local temperature is too low.After the improvement of the duct structure,the wind speed of the outlet is reduced by 10.1%and the temperature of the human body is picked up by 6.2%.Therefore,the structure of the duct has significant effects on the thermal comfort of the human body.For the study of comfort,the widely used comfort evaluation index is PMV-PPD and ASHRAE evaluation criteria.On the basis of the expression of thermal sensory regression in other parts of the study,this paper analyzes the proportion of the four parts of the head,trunk,upper limb and lower limb in the subjective evaluation by using AHP.Furthermore,each part of the expression was assigned a corresponding weight value,and the overall thermal sensation of the occupant evaluation method is obtained,which is of significance in the bus comfort design and air conditioning system research and development.