Automotive lights have become an integral component of vehicle styling and brand identity. In the past they were developed mainly with the focus on technical criteria. However, their design has become a crucial aspect of the vehicles exterior appearance. Additionally, the use of new materials leads to more individualized and more complex geometries, which make it challenging to comply with the technical requirements. For reasons of lightweight construction and economical forming processes, thermosetting and thermoplastic polymers are increasingly used. These materials are considerably more temperature sensitive when compared with metals. Even when using halogen bulbs, the temperature distribution in the headlight geometry gets often critical. In addition to heat transfer, the effective evaporation of condensate films, which can form on the inner part of the lens depending on the weather conditions, is an important criterion for the layout design of headlights. The aim of this work is the development of a methodology which is able to predict both, the temperature distribution in the headlight as well as the evaporation of condensate film, with a good accuracy. Thus, a tool should be provided to the developer that identifies problematic designs and supports their improvement before the actual prototype production. The verification of this method succeeded at the example of the VW Polo headlight, relying on detailed measurements of the flow fields, the temperature distributions and the condensate film evaporation. To validate the numerical simulation of the temperature distribution and water film evaporation of automotive headlights, numerous detailed measurements were carried out. The computation results were essentially confirmed. The buoyancy flow and the temperature distribution were accurately predicted by the simulations. The assumption of diffuse radiation reflection does not account for the specular character of the reflectors. This leads to a difference in the prediction of the temperature distribution at the lens. The prediction of the evaporation of a condensate film on the lens matches well the measured results in the bounds of the measuring accuracy. The wall film model seems to be suitable for the description of the evaporation processes.
Investigation of heat transfer and evaporation processes in automotive headlights
Untersuchung des Wärmeübergangs- und Verdampfungsprozesses in Automobilscheinwerfern
2007
7 Seiten, 6 Bilder, 6 Quellen
Conference paper
English
C640/033/2007 Investigation of heat transfer and evaporation processes in automotive headlights
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