| Summary: | 博士 === 國立清華大學 === 工程與系統科學系 === 95 === Heat pipes are widely used as heat-transport devices because of their superiority of transferring heat within low temperature differences. Recently, the vapor chambers (flat plate heat pipes) are applied on the electronic cooling. However, most of the available analysis models are too complicated to real applications. In the proposed non-lumped model, vapor is assumed as a single interface between wick structures, so the local temperature distribution and the heat spreading effect can be therefore investigated. Furthermore, the non-lumped model can be simplified as a lumped model, which contains four control volumes only. The calculated results are in line with the results in previous literatures and the experiments conducted in this study.
Experimental comparisons between copper/aluminum plates and a vapor chamber having the same thickness have been also conducted. The spreader plates integrated with a plate-fin heat sink are tested in a wind tunnel. For small-area heat sources, the vapor chamber shows a lower thermal resistance and much uniform temperature distribution than the metal plates. Then, the heat sink integrated with the vapor chamber is simulated by using non-lumped model. In order to obtain more accurate transient responses, the heating block and insulation are also considered in simulation domain. From the simulations, the major thermal resistance of the vapor chamber is contributed by the heated wall. The maximum difference of the hotspot temperature rises between the simulation and experiments is 6.3 %.
Additionally, a steady-state three-dimensional heat conduction equation is analytically solved by using separation of variables. The temperature distribution within a partially heated rectangular plate is solved and the spreading resistance is therefore obtained. The analytical solutions show very good agreement with numerical simulations, and they are also in line with the previous correlation and approximation. The spreading resistance of the thin plates with a small aspect ratio is much higher than the one-dimensional conduction resistance.
By adapting the ideas of isotropic or anisotropic heat spreading, the effective thermal conductivities of the vapor chamber have been calculated. The radial conductivity of the vapor chamber is merely 48.74 W/m-K, but the axial conductivity is more than ten times of the radial conductivity. The high axial conductivity can sufficiently enhance the heat spreading along the axial direction, and thereby resulting in a lower total thermal resistance. Combining into the whole module simulation, the surface temperature distribution is similar as that obtained by non-lumped model.
In this study, the non-lumped model is developed and presented. Moreover, the thermal spreading resistances have also been analytically investigated. An anisotropic method to calculate the effective thermal conductivities of vapor chamber is also proposed. Heat pipes, vapor chambers and integrated thermal modules draw lots of attention from cooling industries. However, there was no sufficient model to estimate the performances of the integrated thermal modules. The proposed non-lumped model and calculation of effective thermal conductivities will be helpful to evaluate the performances of vapor chambers, and they will be useful in further designing work of vapor chambers and integrated modules.
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