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The safety and comfort aspects of passenger cars are significant sales argument and have become a topic of rising importance during the development process of a new car. The objective of this study is to compare the performance of several current model vehicles, highlight the drawbacks of current defrosting/demisting systems and point the way to improved passive mechanisms. The investigation is experimental. The experiments are carried out using full-scale current vehicle models. The results show that the current designs of the defroster nozzle give maximum airflow rates in the vicinity of the lower part of the windshield, which decrease gradually towards the upper parts of the windshield. This hinders and limits the vision of the driver, particularly at the top of the windshield, which can be uncomfortable and indeed dangerous.

The air flow distribution in a car from the panel registers to the driver or passenger is largely influenced by the register design. We have undertaken a study using both experimental and numerical techniques to understand the parameters that influence register performance. In particular, we set out to identify the register characteristics that have the greatest effect on the size of the plume. The idea is that once an occupant has reached thermal comfort, particularly after cool down, the less direct impingement of air the occupant feels, the greater his/her comfort.

This paper examines the prevailing fluid flow and heat transfer on the windshield of a full–scale vehicle and examines ways of promoting efficient de–icing and demisting. It establishes that present methods of defrosting and demisting windshields are inefficient; since the first area cleared is below the driver's eye level and even this result only occurs some considerable time after the blower has been switched on. The complexity of the windshield topography and the defroster nozzle geometry yield inadequate flow mixing, poor momentum interchange and consequently dead flow zones in critical visibility areas. This study explores ways of improving the defrosting and demisting process through passive means and using the existing air handling system of the vehicle. The results presented are from numerical simulations validated by experiment.