Numerical Studies on the Effect of Cooling Vent Setting and Solar Radiation on Air Flow and Temperature Distribution in a Passenger Car 2009-28-0048

Owing to the dynamic life style, considerable time is spent in traveling. Consequently, the demand for thermal comfort of passengers in vehicles has increased. And, to provide thermal comfort, the vehicles are equipped with Heating, Ventilation and Air Conditioning (HVAC) systems. However, the tendency to use more glass in vehicle styling, fuel-economy constraints, environmentally safe refrigerants and reduced condenser air flow, particularly at idling conditions, hampers the goal of achieving the desired thermal comfort of passengers. Thus, it is imperative to evaluate the performance of the HVAC units and the effect of their delivery systems to predict the impact on the airflow, temperature distribution and thermal comfort of passengers. CFD simulations have gained importance for such evaluations, which include both steady state and transient calculations.

In this paper, the studies made on the effects of solar radiation and different A/C vent angle settings on the airflow, temperature distribution and the thermal comfort of passengers in a typical medium size car are presented. The baseline study was carried out on the empty car followed by studies on the effects of including passengers in the simulations. Geometric model of the car cabin was created in CATIA V5. The model was discretised using GAMBIT pre-processing tool. CFD analyses on the model, for the baseline case (without passengers) and with passengers, were carried out using FLUENT. Parametric studies on A/C vent angle settings were carried out (the vent angles were varied longitudinally from a default position, wherein the A/C airflow was normal to the dashboard surfaces). The solar radiation incident on the car cabin and the output from the air conditioner were also considered for the CFD analyses.

From the analyses it was observed that the solar radiation heated the exterior and interior surfaces of the car cabin. Also, the presence of passengers altered the flow and temperature distributions in the cabin considerably. The different vent angles also had considerable impact on the air flow pattern and temperature distribution in the cabin, affecting the sensation of thermal comfort by the passengers.