Date of Award

12-2015

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

First Advisor

Dr. Mohammad O. Hamdan

Second Advisor

Dr. Ahmed Hassan

Third Advisor

Dr. Emad Elnajjar

Abstract

This study aims to analyze the cooling performance of phase change materials (PCMs) integrated into metallic heat sinks (HSs) both experimentally and numerically. For the experimental part of the study, a test setup has been constructed to test PCM integrated heat sinks. The heat sinks are prepared as metallic containments having fins with fixed inter-fin spacing. The volume between the heat sink fins is filled with PCM namely: a paraffin wax, salt hydrate-calcium chloride and milk-fat, then the whole system is sealed for testing under various heat loads at 4W, 6W, 8W and 10W. Four modes of operation are experimentally tested in this study: HS under natural convection, HS integrated with PCM under natural convection, HS under forced convection, and HS integrated with PCM under forced ventilation. The temperature of heat generating surface and the heat sink surface are monitored over time to evaluate the PCM thermal performance. From the results, the time lag and temperature drop in case of with PCM compared to without PCM shows the cooling effect of adding PCM under both natural and forced ventilation modes of heat removal. It found that inclusion of each of the three types of PCM into heat sinks with natural convection shows higher temperature drop (up-to 15 °C) in first 15 min of heating than inclusion of fan (forced convection) without PCM. However, the combination of both the fan ventilation and the PCM always maintain the lower temperature other three modes. This leads to conclusion that implementing a PCM in the heat sink will be very useful in thermal management of the electronic device and the application is more suitable under cyclic thermal loading conditions since in all cases the PCM completes melting in certain time and then shows a temperature rise. It is recommended to use forced convection combined with PCM filled in HS to increase the cooling effect while using PCM will be recommended for short time operation or cyclic operation such as switching operations where PCM can be regenerated to solid during off duty cycle to be ready for the next cycle of heat absorption. It is also recommended to use PCM integrated into a HS to provide a backup passive cooling support especially in case of failure of the fan system during operation as an additional safety cover. For the numerical part of the study, a three dimensional transient heat transfer numerical model using commercial ANSYS CFD software is developed and is validated against the experimental results. Next the numerical model is used to optimize the heat sink geometry, the PCM amount and the viii cooling-heating response in order to identify potential applications in electronic packaging in terms of temperature drop and charging-discharging cycle time. From parametric study, it is observed that a narrow melting point, not mixing of the PCM, good thermal conductivity, higher density, rectangular fin type and a reasonable package size are optimum for the temperature control of electronic devices employing heat sink with PCM.

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