Visualization And Theoretical Study On Flow And Heat Transfer In Microgrooves Heat Sinks Based On Micro-PIV

Microscale heat transfer is the main focus in the heat and mass transfer, and new cooling methods based on the microscale heat transfer have been widely utilized in high-power electronical components, low temperature waste heat utilization, high-power laser cooling and LED equipment. Combined phase-change heat transfer in open capillary microgrooves heat sinks is one kind of microscale heat transfer, and its principle of combined phase-change heat transfer in open capillary microgrooves heat sinks is driving fluid to flow along the axial direction of the microgrooves by capillary pressure difference due to the structure of the microgrooves, and forming thin liquid film where there exists high evaporating heat transfer coefficient and thick liquid film where nucleate boiling exists with high phase-change heat transfer coefficient. More attention has been paid to this new cooling method and more research has also been constructed and a lot of results have been achieved.In this work, visualization investigation of the meniscus shape in rectangular capillary microgrooves heat sinks with substrate material of borosilicate glass is conducted with Micro-PFV method. Investigations of the meniscus shape of accommodation, recession and corner flow stages in rectangular microgrooves heat sinks varying with axis under the condition of inclined angle of0,15degrees,25degrees and35degrees with different heat fluxes when the pure evaporation occurs in the rectangular capillary microgrooves heat sinks; data of the meniscus shape are fitted with parabolic curves, and3D profiles of the meniscus shape along the axis of the microgrooves are also attained. Curvature of the meniscus shape along axis of microgrooves is also investigated. Results show that the meniscus shape in rectangular microgrooves heat sinks is quasi-parabolic with heat flux added from below; the meniscus shape does not change along the axis in horizontal microgrooves; heat flux has great influence on the meniscus shape; the curvature of meniscus shape in horizontal microgrooves heat sinks does not vary along the axis, while the curvature of the meniscus shape in inclined microgrooves heat sinks increases along the axis; the meniscus shape of corner flow stage gradually recedes to the corner of the microgroove under the condition of the same heat flux and inclined angle.Visualization research on fluid velocity and flow patterns of rectangular microgrooves heat sinks with substrate material of borosilicate glass and red copper is constructed with Micro-PIV method. Velocity vectors and cross-section area of the liquid in accommodation, recession and corner flow stages are investigated; the velocity distribution in the tangential direction is also studied; flow patterns in different inclined angles are investigated and assumptions by Carton and Stroes have been confirmed. Results show that fluid in microgrooves driven only by capillary pressure difference flows very slowly and is under laminar flow; velocity in thin liquid film region is far less than that in thick liquid film region; the flow pattern confirms that there exist accommodation and corner flow stages; liquid cross-section area decreases along the axis; the fitted curves of the liquid cross-section area along the axis is a conic distribution; curvature of the curves increases with the inclined angle as well as the cross-section area; liquid cross-section area decreases with inclined angle in the same cross-section. The liquid cross-section area in corner flow stage along the axis is a linear distribution and cross-section decreases.The flow characteristics in inclined rectangular microgrooves heat sinks under pure evaporation condition are investigated theoretically, and the axial flow model in rectangular microgrooves heat sinks is revised. The analytical results are compared with the experimental results, such as thickness of the liquid film of the meniscus, curvature and the liquid length of accommodation stage and recession stage, and the liquid film characteristics of the meniscus are derived.Bubble dynamic behaviors and fluctuation of triple-phase contact line and the temperature distribution on the microgrooves are investigated by high speed camera and thermal infrared imager. The fluctuation of the triple-phase contact line caused by bubble-burst, the change of the shape of triple-phase contact line due to bubble-burst under different heat flux, impact of heat flux on fluctuation time of triple-phase contact line, bubble period, bubble-burst equivalent diameter and temperature distribution, influence of superheat on bubble departure frequency are all investigated. Results show that bubble-burst makes triple-phase contact line fluctuate periodically; with increase of the heat flux, the amplitude of the triple-phase contact line increases and wavelength elongates, so fluctuation becomes violent and the fluctuation region gets wider; fluctuation time first increases and then decreases, and there exists a peak value; the bubble period decreases with heat flux; bubble-burst equivalent diameter increases with heat flux; bubble-burst equivalent diameter increases with the microgroove width under the condition of the same heat flux and microgroove depth; temperature of the surface of the microgrooves heat sinks shows a trend of fluctuation, and there exist peak and trough values; the mean temperature of the surface of the microgrooves increases with heat flux; temperature of the region of the bubble-burst shows a peak value in nucleate site in3D temperature profiles.