Microstructure design of PCM infiltrated copper composite through freeze casting method toward maximized heat absorption rate
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Date
2022-01-01
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Department
Mechanical Engineering
Program
Engineering, Mechanical
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Distribution Rights granted to UMBC by the author.
Access limited to the UMBC community. Item may possibly be obtained via Interlibrary Loan thorugh a local library, pending author/copyright holder's permission.
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Abstract
Thermal management of electronics is becoming increasingly difficult due to the trend of miniaturization in modern electronics. Modern electronics also pose a challenge due to pulse heating, or intermittent spikes of high heating that occur for less than one second. Studies have found that composites made of a conductive component and a phase change material (PCM) can be used to effectively mitigate overheating due to pulse heating without overdesigning the heat sink. This is due to the conductive capacity of the conductive component in conjunction with the high thermal storage capacity of phase change materials. A theoretical study based on phase change in homogeneous media is performed to determine the best microstructure of the composite as well as the optimal composition of the conductive component (copper). It is found that a lamellar microstructure infiltrated with PCM outperforms a disordered porous foam microstructure infiltrated with PCM for both low and high heat fluxes. It is also found that an optimal composition by volume exists for the lower heat fluxes studied and a critical composition of 30% by volume is found for the higher heat fluxes studied, above which there is no substantial decrease in the interface temperature.
Then, a numerical study at pore scale is performed to simulate simultaneous heat transfer and phase change in a unit cell of lamellar porous copper infiltrated with paraffin wax. The simulation is used to determine the effect of lamellar spacing (pore size) on the thermal management performance of the composite for different heat fluxes. This study is also performed to determine the effect of material properties, specifically thermal conductivity, on the optimal pore size. It is found that the effect of pore size is more pronounced at higher heat fluxes, showing that there is a need for application-specific microstructure design. It is also found that the effect of pore size is more pronounced for materials with higher thermal conductivities, and these materials require a smaller pore size for more efficient thermal management. For higher heat fluxes, a pore size on the order of tens to hundreds of microns is required, and a smaller pore size is not necessary to achieve better thermal management performance.
Finally, fabrication of these microstructures is investigated using the novel freeze casting technique. While this technique is well established for the fabrication of ceramic materials, it has not been extensively studied for the fabrication of porous metals. It was found that this method can be used to produce porous cupric oxide structures with low (approximately 9 vol.%) solid loading, as well as higher (approximately 12 vol.%) solid loading with the addition of potassium hydroxide (KOH). Pore sizes were created ranging from tens of microns to hundreds of microns. It is expected that future research can lead to better control over these microstructures through manipulation of the suspension composition as well as manipulation of the freezing rate of the suspension. It is also expected that future studies can use reduction and sintering techniques to produce a pure copper lamellar microstructure.