Analytical Simulation of Automobile Windshield Defogging

Visibility in the automotive industry is a major source of concern for the car manufacturers and safety design engineers. Water film (fog) that forms on the windshield during winter times would reduce and disturb the driver’s visibility. This water film is originating from condensing water vapor on the inside surface of the windshield due to low outside temperatures. Primary source of this vapor is the passenger’s breath, which condenses on the windshield. Warm and dry air, which impinges at certain velocity and angle relative to the windshield, will reduce the thickness of this water film (defogging) and hence improves driver’s visibility. Therefore, a well-designed HVAC system will help reduce this water film thickness to an accepted level for visibility. CFD technology can be utilized to study the defogging process by tracking water vapor content and predict transient variation of condensed water layer on the glass surface. An analytical approach to simulate the defogging process including removal of the water vapor from the passenger cabin glass is discussed. The pre-processing including grid generation was performed using ICEMCFD. The transient thermal CFD simulation was performed using Fluent.

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