Multi-dimensional modelling of evaporation in the micro region of a micro grooved heat pipe

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2015
Akkuş, Yiğit
Capillary cooling devices are preferred in heat removal from electronic components which are characterized by high heat dissipation rates. Heat pipes use various wick structures to generate the necessary capillary action. Heat pipes that use grooved micro-channels as wick structures, have been widely studied by researchers due to the fact that their simple geometry enables the modelling of fluid flow and heat transfer both analytically and numerically. Near the attachment point of liquid-vapor free surface to the groove wall tip, there exists an extended meniscus geometry which is generally known as the micro region. The low thermal resistance across the evaporating thin film of the micro region enables high heat transfer rates, and a considerable amount of the evaporation originates from this region. In the literature, evaporation has been modelled using the unidirectional flow assumption of the liquid. In the present study, the three directions of the liquid flow are considered. This thesis solves the evaporation in the micro region with the unidirectional flow model starting from a location where the effect of disjoining pressure is small. Unlike many studies in the literature, the boundary conditions defined at the starting point are not tuned during the solution procedure to match the undisturbed meniscus radius. The results of the unidirectional flow based model reveal that the curvature of the film thickness profile may change its sign and bends inward near the contact line depending on the physical system considered in the problem. Following unidirectional model, the present study applies the spectral element method to solve the linear momentum equations in order to get the effect of vertical flow of the liquid. Although the amount of inlet mass flow or the film thickness profile is not changed substantially with the application of bi-directional flow based evaporation model, determination of the distribution of vertical velocity in the micro region enables understanding of the underlying physical phenomena. Finally, the contribution of the axial flow to evaporation is investigated by solving the distribution of axial velocity using spectral element method and the contribution of the axial flow to evaporation is found to be negligible. Systems which form small apparent contact angles at a definite superheat, are found to have higher heat removal capacity.
Citation Formats
Y. Akkuş, “Multi-dimensional modelling of evaporation in the micro region of a micro grooved heat pipe,” Ph.D. - Doctoral Program, Middle East Technical University, 2015.