Plastics are a common material in automotive lamp design used for housings, lenses and bezels. Halogen bulbs together with small lamp dimensions and/or additional heat loads coming from the engine compartment often cause high temperature loads to the lamp. The use of plastics increases the problem because of the low thermal conductivity, which makes it difficult to let flow the heat towards colder regions. Temperature homogenization is hindered so that unfavorable hot spots may occur. In general the heat load is due to conduction, convection and radiation, which may occur in single mode or in any combination but with a different weighting depending on the boundary conditions. A thermal analysis of a lamp has to consider all three heat redistribution mechanisms in a coupled manner within the whole geometry. There is evidence that a quantitative solution is hardly to be achieved by analytical means if one looks at the basic equations which are coupled and highly non-linear. Furthermore several materials applied in lamp design are selective radiators indicating a multi-band radiation approach. Because of this a numerical analysis is the means to choose. In the paper the influence of natural convection flows and radiative heat redistribution on the temperature field of an automotive fog lamp is studied. The thermal analysis was done with the commercial computational fluid dynamics package CFX-4. The three-dimensional, steady-state analysis accounts for natural convection flow and radiation within the entire fluid domain, which contains the filling gas of the bulb and the air inside and around the lamp. Conduction is taken into account within the housing. Bulb and lens are treated as translucent conjugate heat transfer (CHT) objects. Radiation is modelled by a multi-band ray-tracing approach which is solved with a Monte-Carlo scheme.
Radiative heat redistribution and natural convection flow inside an automotive fog lamp
Wärmeverteilung und natürliche Konvektionsströmung in einer Fahrzeug-Nebelleuchte
2005
11 Seiten, 7 Bilder, 5 Quellen
Conference paper
English
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