Analysis of Defogging Pattern on Windshield and Ventilation Load Reduction based on Humidity Distribution Control 2016-01-0256

In the winter, windshield glass fogging must be prevented through the intake of outdoor air into a vehicle. However, the corresponding energy loss via the ventilation system cannot be ignored. In the present study, the defogging pattern on the windshield is evaluated and the water vapor transportation in the flow field in the vehicle is analyzed in order to investigate the ventilation load by means of a numerical simulation. Some examined cases involve new outlet positions. Additionally, a new, energy-saving air supply method for defogging, with so-called “double-layer ventilator”, is proposed. In this method, one air jet layer is obtained via a conventional defogging opening in the vicinity of the windshield, supplying an outdoor air intake. The other jet consists of recirculated air that covers the outdoor air, preventing it from mixing with the surrounding air. The calculation results indicate that the exhaust opening location, from which the internal vehicle air is obtained for recirculation, affects the cabin flow field, the windshield fogging pattern and the ventilation load. The water vapor generated from human occupants did not spread well and that is why there was the humidity gradient in the vehicle. This means that the flow field must be considered in order to achieve efficient defogging, that is done by emitting the water vapor immediately. The double-layer method exhibits the same level of defogging performance as single-layer techniques, even with half the airflow velocity. The energy load can be reduced by approximately 5 % using the appropriate conditions.