Study On Internal Flow Field Characteristics Of Passenger Compartment Under Parked Car Ventilation For Temperature And Humidity Control

Automobile companies have to make their products not only have advantages in cost,performance and appearance but also have excellent comfort and user experience so as to enlarge their market shares in the increasingly competitive auto market of China.The performance of modern vehicle HVAC system has basically met the demand of different driving conditions.However,there is little research on improving the passenger compartment climate in parked cars under adverse environmental conditions.In this paper,the ventilation function of vehicle HVAC system was used to control the temperature and humidity of passenger compartment of a parked car for cooling after hot soak in summer and preventing frosting on the windshield in winter,which could enhance the comfort and user experience when occupants get into the car.In order to obtain reliable results from CFD simulation,methods of physical properties setting,thermal radiation simulation and humidity calculation,adopted for cooling or dehumidification simulation in this paper,were chosen based on the mechanism of hot soak and frosting and the effect of ventilation on temperature and humidity control.Then model experiments were performed in summer and winter respectively and the experimental data was compared with simulation results to prove that these methods were valid and simulation results were accurate.The winter model experiment was also shown that parked car ventilation could prevent frosting on windshield internal surface.After that,effects of total air volume,air distribution and air direction of parked car ventilation on cooling and dehumidification were studied by simulation with the proved methods and experimental conditions on a passenger compartment.Conclusions were drawn and the mechanism was investigated from the perspective of internal flow field characteristics,which provides theoretical support and design guideline for further research and application.Increasing cold air jets from defrosting inlet can speed up the air flow around windshield internal surface and lead to stronger convective heat transfer,which is the most effective way to cool the windshield in winter.When defrosting mode air door fully opens,high velocity upward air jets from air-conditioning inlet can cause steady large vortices and high speed flow in the cabin that promote the mixing and discharge of air,and accelerate both passenger compartment cooling after hot soak in summer and dehumidification in winter.Moreover,the air temperature falls slowly after the rapid cooling in the first 3 minutes because of the influence of solar radiation and heat from the thermal mass after summer hot soak.Water vapor concentration drops quickly before dehumidification efficiency reaches 90%,and then dehumidification rate decreases and tends to zero until absolute humidity inside and outside the car is equal.