|M.Sc Thesis||Department of Mechanical Engineering|
|Supervisors:||Prof. Emeritus Hetsroni Gad|
|Prof. Emeritus Shitzer Avraham|
|Full Thesis text|
This study presents an optimization procedure for the design of a Latent Heat Thermal Management System (LHTMS) for an electronic device with a transient and high heat generation. The LHTMS consists of a Phase Change Material (PCM) combined with internal fins which are used for creating high conductive paths into the PCM. The aim of the optimization is to produce a design of the LHTMS with a minimal height while still withstanding the heating of 200 W, generated by the electronic device, without exceeding the maximum allowed temperature of 60 °C.
A review of candidate PCMs is presented along with an evaluation and a comparison between them.
The optimization itself is performed by varying the number and thickness of internal fins of the LHTMS. Once the optimum combination is chosen, further analyses are performed for obtaining the required height of the LHTMS, which satisfies the performance requirements.
The numerical method used in the study is the Finite Elements Method (FEM) which uses the enthalpy method in order to obtain solutions for problems involving the change of phase. Due to the latter, several experimental methods were used in order to obtain the enthalpy-temperature dependence of the chosen PCM.
Once the design has been completed, an LHTMS was manufactured and its performance was compared to the calculated one.
From the comparisons, it was concluded that large differences between the experimental and the FEM results might occur. These differences seem to occur due to presence of significant internal convection in the PCM, which is neglected in the numerical model. These differences could also result from paucity of knowledge of the exact thermo-physical properties of the chosen PCM and the asymptotic approximation made to its enthalpy.
In addition, the experimental LHTMS was filled and tested with water. The results show that internal convection is present in the water, thus raising the calculated performance by up to a factor of two and almost matching it to the performance of the PCM filled LHTMS. Since the PCM used in this study (ClimSel C48) contains approximately 40% water in its liquid phase, the last result further verifies the existence of internal convection inside the PCM.
It was also demonstrated that reducing the heating rate to 100 W results in significant increase of the LHTMS effectiveness, thus leading to a superior performance when compared to equivalent water filled LHTMS.