Design and Development of Demisting Device of a Commercial Vehicle and its Numerical as Well as Experimental Validation

Adequate visibility through the vehicle windshield over the entire driving period is of paramount practical significance. Thin water film (fog) that forms on the windshield mainly during the winter season would reduce and disturb the driver’s visibility. This water film originates from condensing water vapor on 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. Hot and dry air which impinges at certain velocity and angle relative to the windshield helps to remove the thin water film (defogging) and hence improves driver’s visibility. Hence a well-designed demisting device will help to eliminate this fog layer within very short span of time and brings an accepted level of visibility.

An attempt is made here to design and develop a demisting device for a commercial vehicle with the help of numerical and analytical approach and later on validated with experimental results. System configuration was finalized by analytical method followed by 3D (dimensional) modeling in CATIA. Steady state and transient computational fluid dynamics (CFD) analysis were carried out in CCM+ to predict the striking zone, airflow mapping over the windshield and transient defogging pattern respectively. The predicted transient behavior of windshield defogging was validated with experimental results obtained from prototype sample of demisting device. The numerical results of airflow mapping and transient defogging pattern were in good agreement with that of experimental data. Thus a methodology is developed which is very useful in reducing the number of prototypes, testing cost and the project development timeline by adopting numerical and analytical approach in the early stage of design and development cycle.