Temperature Field in a Floodlight

The company ARRI Lichttechnik is a worldwide leading producer of lighting equipment for, e.g., studio technology and motion-picture production. The floodlights produced by the company ARRI provide a significant thermal output due to their strong luminosity. Measurements taken by ARRI have shown that temperatures of several hundred degrees Celsius occur in the interior of the floodlights, which might damage the highly sensitive electronic parts if no countermeasures are taken.

In studios or at motion-picture sets, the use of ventilators is impossible due to unacceptable noise. The floodlights are therefore cooled by convection. The floodlight cases are provided with openings, so that cool air streams into the interior, is heated at cooling plates, thus cooling the interior, and leaves the floodlight as hot air. These processes have been made visible in the framework of the project by computer simulation.

Temperature and Surface Radiation

The heating of the floodlight is primarily due to surface radiation, which is emitted from the wreath filament depending on its temperature and thermal output, and is subsequently subject to multiple reflections within the floodlight. Other components of the floodlight case are also radiating, depending on their temperature. In the interior of the primarily metallic components of the floodlight, heat is transported by usual heat conduction.

The air is now heated at the surfaces of these components, which initiates a convective flow. This convective flow has been modeled by the Navier-Stokes equations and the so-called Boussinesq approximation. The temperature-depending differences of density in the air are only accounted for by a so-called lift term of the impulse equation, they are not accounted for in the continuity equation.

FLUENT® for Numerical Computations

Possibly disturbing sound waves are thus avoided from the beginning, which improves numerical stability and reduces computing times. At the contact interfaces, temperature continuity and the reduction to zero of the entire heat balance was required, whereas at the exterior boundaries of the computing domain, requirements were pressure continuity and the reduction to zero of the entire mass flow. 

Numerical computations were carried out by the commercial software package FLUENT®, where discretized versions of the relevant equations are implemented. FLUENT® is a numerical method using the finite volume method; the computing domain must therefore be divided into smaller cells by a grid. However, the floodlight geometry is very complex, so that several geometry simplifications became necessary for the so-called meshing. These simplifications were to remain without essential influence on the results as far as possible.

Simulation Results

The simulation results show the formation of a convective flow through the floodlight essentially from bottom to top, as expected. The temperatures of the individual components correspond very well to those measured by ARRI. The methods developed within this project are thus able to offer considerable advantages concerning the future design of floodlights.

Type of Project: Industry Project
Project Partner: ARRI Lichttechnik