A Visualization Study Of Microgrooves Structure Effect On The Bubbles Dynamic Behavior On The Surface With Micro-nano Composite Structures Heat Sink

A nano coating is deposited on the surface of microgroove heat sinks,which forms micro-nano composite structures.The micro-nano composite structures have the characteristics of the micro structures and the nano structures simultaneously.So the micro-nano composite structures have more unique features of heat transfer enhancement.The study of micro-scale effect on the bubbles dynamic behavior on the surface with micro-nano composite structures is important to develop and enrich the theory of phase change heat transfer on the micro-nano scale,which has an important academic value.As for application in engineering,research results of this subject can provide theoretical basis for design of micro-cooling system for electronic devices with high heat flux.It also has great significance for promoting the development in electronic industry of our country.The visualization study of the bubble dynamics behavior on the surface with micro-nano composite structures with different microgroove structures placed vertically is implemented by high-speed photography technique.The borosilicate glass microgroove plates fabricated by dicing technology are coated with 250 nm titanium nano coating by magnetron sputtering system to generate micro-nano composite structure surface.Experiments were conducted using distilled water as the working fluid under saturated and atmospheric conditions.The temperature of distilled water was maintained at saturation temperature using the heating and temperature control system,then the micro-nano composite structure heat sink was heated through the ceramic heating plate.When the system reaches steady state,the bubble dynamics behavior on the surface with micro-nano composite structures was observed and photographed by the high-speed camera.The temperature of the heat sink and the PTFE thermal insulator were recorded with data acquisition instrument.The high-speed images obtained during experiments were processed using the software PCC2.3 and MATLAB to calculate the equivalent diameter of the bubbles at each stage of growth process.The shooting rate of the high-speed camera is 6000 frames per second and the interval between every two frame is 0.17 milliseconds.We can calculate the bubble period and the bubble waiting time by the frames in the bubble period.According to the experimental results,at the same heat flux,bubble equivalent diameter,bubble period,and the waiting time decrease with the increase of the ratio of depth to width.For the same microgroove size of the micro-nano composite structure,when bubbles rupture,the equivalent diameter decrease with the increase of heat flux.At the same heat flux and microgroove size,the bubble equivalent diameter in the micro-nano composite structure less than those in microgroove structure without nano coating.Regardless of the difference of microgroove size and nano coating,the bubble period and waiting time decrease with the increase of heat flux.The results show that compared with microgroove structure without nano coating,the differences of microgroove size of micro-nano composite structure have more significant effects on the changes of the bubble dynamics behavior.