Experimental Study On The Impact Of Bubble Dynamics On Solid-Liquid-Vapor Triple-Phase Contact Line In Capillary Microgrooves

For capillary microgrooves heat sink, the combined heat transfer of evaporating heat transfer in the extended thin film region and nucleate boiling heat transfer in the intrinsic meniscus region occurs at higher heat load. It has been used to achieve heat exchanges with high heat transfer coefficient and heat flux. So capillary microgrooves heat sink can be designed to meet the stringent cooling demands of LED, high power lasers, manned space flight technology, waste heat utilization in power station and high power microelectronic devices.The main purpose of the present thesis is to clarify the impact of the bubble dynamic behaviors on the triple-phase contact line in the heat sink of open capillary microgrooves and phase-change heat transfer during nucleate boiling heat transfer process in capillary microgrooves experimentally, thereby gain comprehensive understanding of enhanced heat transfer mechanisms in this heat sink and lay the foundation for the design of micro-cooling system.The boiling phenomena in capillary microgrooves heat sink is captured by using a high-speed camera with the maximum speed of 100000 frames per second and a microscope. The rectangular microgrooves are processed on transparent borosilicate glass. Distilled water is used as cooling liquid. The regulation of the contact line waving impacted by the bubble dynamic behaviors and the relation between the waving characteristics and the physical dimension are studied. In the initial period of the boiling, the contact line appears as a sunken, and then it forms as V-shape and W-shape. At last the contact line becomes steady until the next boiling process.It is found that for the microgrooves with the same geometric size, the swing of the waving becomes high with increase of the heat flux. If under the same heat flux, the scope of the waving is restricted by the width of the microgrooves and the swing of the waving is small. For the microgrooves with the same groove width, the swing of the waving is high in deeper microgrooves. For the microgrooves with the same depth-width-ratio, the scope and the swing of the waving are large in deeper and wider microgrooves.According to the experiment, as the bubble bursts, the liquid from the micro layer on the top of the bubble jumps out of the microgrooves with the break of the bubble during the boiling process. When the liquid drops splash from the grooves, the liquid in the microgroove will refill the place where the liquid drops have spilled and the new liquid cannot be heated to the saturated boiling condition. The latent heat of vaporization of the splashed liquid drops could not be utilized when the liquid drops spill from the microgroove. Compared to the sensible heat, the latent heat of water is apparently greater. The amount of latent heat loss is related to the heat flux input and the dimensions of the microgrooves. There is more latent heat lost in deeper and wider microgrooves.