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CFD has been actively applied for developing automotive air conditioning system in recent years. In addition to automobile interior air conditioning, an automotive air conditioning system has the important function of providing a clear field of view by defogging (or defrosting) the windows. Although many CFD application methods have been reported for estimating windshield defogging pattern, few examples of simulation show accurate result of transient clearing pattern. To predict transient clearing pattern accurately, using a correct model of window glass fogging-clearing is important. As the result of our observation on fogged glass surfaces, fogging was found out to be an aggregation of water drops, so that new dropwise condensation-evaporation model was developed and applied. Transient defogging patterns were simulated with the CFD code including this model, and accuracy was verified on a simplified compartment model and actual automobiles.

Vehicles have been more required to save energy against the background of the tendency of ecology. As the result of improving efficiency of internal combustion engines and adoption of electric power train, heat loss from engine coolant, which is used to heat the cabin, decreases and consequently additional energy may be consumed to maintain thermal comfort in the passenger compartment in winter. This paper is concerned with the humidity control system that realizes reduction of ventilation heat loss by controlling recirculation rate of the HVAC system by using highly accurate humidity sensor to evaluate risk of fogging on the windshield. As the results of the control, fuel consumption of hybrid vehicles decreases and maximum range of electric vehicles increases.