Investigation of Gallium Phase Change Material Heat Sink for CubeSat Thermal Management

  • Haokun Zhang

Student thesis: Master's Thesis

Abstract

CubeSat is a miniaturized satellite with the size of multiple 10×10×10 cm3 . During its operations, heat generated by onboard electronic components needs to be dissipated effectively. Due to the compactness of CubeSat, heat dissipation is challenging given the amount of heat generated confined within a limited space. Among the passive thermal management technologies, gallium phase change material (PCM) heat sink is a promising solution given gallium favorable thermophysical properties and its effectiveness in storing excess heat temporarily in the form of latent heat. However, the phase change heat transfer in a PCM heat sink is complex. Successful application of gallium PCM heat sink technology requires a good understanding of various coupled transport processes. This project aims to design and investigate computationally the operation of a gallium PCM heat sink in a CubeSat subjected to transient thermal loading. In terms of numerical methodology, the enthalpy method is implemented in COMSOL Multiphysics to capture phase change heat transfer process. In this study, the design of a porous medium gallium PCM heat sink evolves from a simple single casing, double casing, pin-fin enhanced and finally to CNT nanoparticle enhanced gallium PCM. The casing is constructed from aluminum nitride (AlN) ceramic for metallurgical compatibility with gallium. Polyvinyl fluoride (PVF) is integrated in the form of porous matrix within the heat sink to address phase change induced volumetric expansion/contraction. Numerical models are constructed to assess the performance of these designs and guide the design process itself. Single casing design is shown to satisfy the operating temperature requirement of the targeted CubeSat based on actual heat generation during its operation. For further improved heat dissipation performance, this thesis proposes a double-casing design with an aluminum outer casing to spreading the heat more uniformly for effective dissipation. A detailed parametric study to optimize appropriate aluminum outer casing wall thickness is performed. Based on the double-casing design with optimal aluminum outer casing wall thickness, internal pin-fins are incorporated to conduct heat more effectively from the heat sink inner surface to outer surface for improved radiative heat dissipation to space. The effects of number and diameter of pin-fins are assessed. The results reveal that the addition of pin-fins only very minimally improves the heat sink thermal performance attributed to the absence of buoyancy-induced convective heat transfer. Further heat transfer augmentation is pursued by adding carbon nanotubes (CNTs) into gallium to form nanoparticle-enhanced PCM. A porous medium nanoparticle-enhanced gallium PCM heat sink is developed. The effect of volume fraction is assessed. It is found that the higher nanoparticle volume fraction increases the thermal diffusivity of PCM and the overall average temperature.
Date of AwardJun 2022
Original languageAmerican English

Keywords

  • Phase change material; Porous media; Gallium; CubeSat thermal management; Pin-fins; Nanoparticles.

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