Multiphase CFD Analysis of Condensation in Automotive Headlamps

A new 3D CFD multi-phase model to simulate the water condensation-evaporation processes

ABSTRACT

EnginSoft implemented a new 3D CFD multi-phase model to simulate the water condensation-evaporation processes inside automotive headlamps for Automotive Lighting, a leading supplier of quality headlights to the OEM market. The scope of this project was to provide the company a simulation tool that would assist in the design of an advanced headlamp with a highly reduced propensity to form internal condensation and that would dispose of any condensation formed within a fixed time. Problem Definition

Problem Definition

With the new state of the art design of more aesthetically pleasing headlamps, and the use of transparent plastic lenses that allow the naked eye to penetrate the headlamp, came the problem that vapor condensation is also very visible. Since the presence of condensation inside the headlamp can be perceived by the customer as a lack of quality and reliability, the company was researching a way to substantially reduce its occurrence and removal time and in the headlamps.

In general headlamp OEM customers define their own benchmarks in which cold air and rain conditions are considered for testing headlamps; a headlamp design can be produced only if the condensation is completely removed in a fixed period of time. 

Up to the point where EnginSoft was brought on board, the most used solution to this problem had been trial and error procedures for the optimization of the headlamps in terms of internal air flows and temperature distribution on the lens. This of course resulted in a long production cycle and high costs. 

The CFD Solution

Once faced with this problem, EnginSoft engineers characterized it as a typical multi-phase problem in which it is important to properly describe the phase change between liquid water and water vapor. To this end EnginSoft designed a multi-phase model implemented inside ANSYS CFX which describes the phase change processes occurring on the headlamp lens and can be efficiently used on long transients for studying the condensation-evaporation processes. The model accounts for:

• latent heat absorbed by evaporation and released by condensation
•  heat transfer between humid air and headlamp components (walls, lamps, reflectors, etc.)
•  thermal radiation when lamps are switched on
•  buoyancy effects of air masses with different temperature and humidity

The model was applied to specifically designed prototypes in which the condensation process was enhanced, as well as to real-world headlamp designs. In all cases the numerical results concurred with measurements from the experimental tests performed by Automotive Lighting in a dedicated and controlled climatic chamber.

"EnginSoft helped us gain a better understanding of the condensation-evaporation processes occurring inside automotive headlamps. With their help we have designed high performance headlamps that fulfill all our OEMs requirements while reducing production time and cost."

Sergio Zattoni
Automotive Lighting