Publication Date

Summer 2018

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Advisor

Raymond Yee

Subject Areas

Mechanical engineering

Abstract

The A Toroidal LHC ApparatuS (ATLAS) strip tracking detector is scheduled to be upgraded in 2025. The order of magnitude for the hit densities and the radiation damage are expected to increase. When radiation increases, the leakage current increases and the heat generated at the silicon trackers can lead to thermal runaway. Cooling is critical in these detectors.

In this study, a glassy graphitic foam was developed by AllComp Inc.~as a precursor to the adhesives (glues). Graphene\textsc{\char13}s highly anisotropic thermal properties result in high thermal conductivity in the planar direction, while it is low in the normal direction. In these conditions, it is interesting to analyze how varying thickness of the thermal interface materials (TIMs) optimizes for effective thermal conductivity. It was hypothesized that the direction where heat enters the graphitic foam and the size of the cross-sectional area normal to the heat flux direction would affect the overall effective thermal conductivity. Furthermore, the overall effective thermal conductivity is likely reduced when a gap is created between ligands and the bonded surface. In this study, a computational approach was adopted, in which a model was developed using the finite element method. From the simulation results, it was found that 0.2 mm thickness of glue provides a better heat transfer at the interface. Using this thickness, the effective thermal conductivity was found to increase by 2.2\% to 5.7\% depending on the thermal conductivity of the selected filler. The amount of surface area contact between the bonded (titanium) surface and the ligands also alters the required thickness of the glue to reach the heat flux saturation in the graphitic foam. The results demonstrate that the parameters at the interface can be optimized to improve the overall heat transfer via conduction.

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