Thermal Analysis and Design Improvement of Light Module Fixture

Introduction:
One of the products made by SAAB Avionics Systems in Jönköping was in need of a better cooling solution. The product, a Head-Up Display, holds a LED that was overheating when run at desired input power. The purpose of this thesis was to identify the design weaknesses in the current solution regarding heat dissipation and produce new design proposals that fulfill the requirements. The parts analyzed consist of a LED light source, adjustment plates and a heat sink. The adjustment plates and heat sink where covered in a surface treatment.

Theoretical framework:
A simulation of a finite element model was set up of the current solution in order to identify the influence of the different parts and their thermal properties. The simulation was set up as a steady state thermal model. The FEM and steady state equations used during this are mentioned and shortly explained. The state of modern research was found in order to find new innovative ways of solving the heat problem.

Method:
In order to understand the current solution, experiments were carried out. Interviews were used in order to get the correct information easily. A literature study was preformed to understand the different theories.

Reverse engineering was applied to get a detailed understanding of the functionality both mechanically and thermally. Brainstorming was used to generate new solutions, which was followed by a feasibility evaluation and Pugh’s method to sort out the best concepts.

Implementation and Result:
Based on the simulations it can be concluded that some of the developed solutions pass the requirements and can be implemented right away. Some need some more work in order to fully pass the demands.

Conclusions:
The thermal flow was greatly affected by the properties of the aluminum in the adjustment plates and heat sink, though there was not much room for thickness reduction. However, the oxide layer and the surface roughness also had a great impact on the high junction temperature.

The requirements where therefore met when adjustment plates and interfaces were removed, to lower the amount of oxide and air between the LED and the heat sink. But the oxide layers needed to be thinner and the surface roughness needed to be reduced in order to meet requirements.

If the oxide layers need to stay at current thickness or the surface roughness cannot be changed, the heat sink needs to be redesigned. The recommended concepts were smaller than the current solution. If this space is utilized with a bigger heat sink, the goals can be met with greater ease. There is also room for improvement when it comes to heat sink heat spreader pattern.

Discussion:
The discussion covers what knowledge which was needed to write this thesis and how different problems that occurred along its path were solved. Sustainability in different ways was also discussed.
Source: Jönköping University
Authors: Lindén, Ronja | Samuelsson, Henrik

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