Date of Award

Summer 2021

Document Type

Open Access Dissertation

Department

Mechanical Engineering

First Advisor

Chen Li

Abstract

Heat pipes are known as efficient two-phase heat transfer devices and widely utilized in thermal management of power plants and electronics. The hybrid mesh-groove wick promises to attain a higher thermal performance of the heat pipe by balancing the permeability and capillarity. However, traditional fully hybrid mesh-groove wick presents considerable condensation thermal resistance due to the condensed quiescent working fluid and thick, saturated wick.

In this study, a novel partially hybrid mesh-groove wick has been proposed to enhance the evaporation of L-shaped copper-ethanol heat pipes. L-shaped heat pipe promotes high-efficient draining of condensed liquid by gravity, while traditional straight-shaped heat pipe encounters unwanted flooding in the horizontal condensation section. The experiment has been conducted to optimize the coverage length of the hybrid mesh-groove wick, including grooved wick, partially hybrid mesh-groove wick, and fully hybrid mesh-groove wick. The results demonstrate that the partially hybrid wick substantially outperforms the grooved wick and fully hybrid wick. The highly efficient capillary evaporation enabled by the mesh-groove hybrid wick is the main factor. However, such hybrid wick cannot be applied in the condensation section owing to thick liquid film confined by the hybrid wick.

Besides, this study has also investigated the effect of mesh-layers number and charging ratio on the thermal performance of the L-shaped partially hybrid mesh-groove wicked heat pipe (LPHHP). Furthermore, a regression analysis method in machine learning has been explored to optimize the charging ratio of the LPHHP. The optimal charging ratio is in a region influenced by the heat load rather than a constant value as a traditional view.

Also, the 3D capillary flowing process of both groove and hybrid wick has been simulated using the CFD method. Simulation results present that the capillary filling process can be significantly enhanced by the mesh-groove hybrid wick in comparison with the groove wick. The enhanced mechanism of the hybrid wick is an extra meniscus on the upper wire surface, resulting in higher capillary pressure. Lastly, a bioinspired contracting mesh-groove hybrid wick has been proposed for the fastest capillary filling. The channel width ratio has been optimized using the CFD method. The optimal width ratio is demonstrated to be 0.5, with a normalized time of 78.2% compared to the straight-channel hybrid wick.

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