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Condensation occurrence in automotive headlights can be detrimental to consumer acceptance of a product. This paper describes a technique for transient numerical simulation of liquid film formation on surfaces during lighting thermal analysis performed using Computational Fluid Dynamics (CFD), including how the film’s properties influence the thermal solution. The numerical technique presented accounts for the change in the film thermal state and thickness due to heat exchange with external fluid flow and solid bodies, surface evaporation/condensation, melting/crystallization within the film volume, and its motion due to gravity and friction forces from the surrounding airflow. Additionally, accurate modeling of radiation effects is critical for lighting applications, including the attendant influence on the thermal distribution of the solids that may have surfaces subject to condensation.

This paper contains a brief description of the numerical approach used to simulate the flow of cavitating liquids that was implemented in FloEFD™ software. Some computational results obtained using this approach are presented. The calculations used 3D Navier-Stokes equations coupled with the k-e turbulence model and equilibrium cavitation model. It is assumed that this process occurs at a fixed temperature (so-called isothermal cavitation). The validity of this assumption is confirmed by numerous test data. Since the liquids heat capacity is large enough to neglect the heat generated in the phase transition, it practically doesn't change the liquids temperature. This approach allows a minimized number of required thermodynamic properties of the liquid.