Fabrication of Micro Nozzle and Micro Impingement cooling heat transfer Experiments

• Main Authors: Kuo-Chung Yen, 顏國忠
• Other Authors: Chie Gau
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/79290006695311763762

碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 92 === 　　Micro-scale impingement cooling process has a very high potential application in cooling a micro-thermal or a high heat flux IC circuits system due to its capability of removing a large amount of heat over a small micro-area. 　　The objective of this study is to design and fabricate a micro nozzle in a size form 5 um to 25 um. This micro nozzle is then used to blow a micro air jet that can be used to impinge and cool a heated thermal chip. The entire thermal chip system is then placed vertically on an optical holder and can be moved vertically in micro-scale by a precision screw on the holder. The structure of this micro jet and the impingement cooling heat transfer over the thermal chip will be studied. The nozzle is made with Si wafer using wet etch ( TMAH、isotropic ) coupled with dry etch ( Anisotropic ) process. This nozzle is rectangular in shape and has 4000 mm in length. The width of the nozzle has three different sizes, i.e. 25 mm, 10 mm and 5 mm, that can be accurately measured. 　　The experimental measurements include flow visualization of the micro jet and impingement cooling heat transfer over the thermal chip. Flow visualization is made by smoke generation that is facilitated by a vertical thin, electrically heated wire coated with oil. The oil is actually supplied by an oil pan on the top of the wire. The jet stream appears to be very stable and maintain its original structure very long until it breaks down on dies out. The breakdown length of the jet becomes shortened when the Reynolds number increases due to the increase in the velocity of the jet. 　　During the impingement cooling experiments the Reynolds numbers varies from 6 to 80, and the nozzle-to-spacings (Z/B) ratio from 4 to 16000. The location for the occurrence of maximum stagnation point Nusselt number approaches the nozzle as the Reynolds number increase.When Reynolds number is kept constant, the Nusselt number and the heat transfer coefficient have increasing with decreases the nozzle width. 　　An attempt was first made to correlate the stagnation point Nusselt number in terms of relevant nondimensional parameters such as the Reynolds number and Z/B. This is done by first normalizing Z/B by dividing Z/B with L/B, i.e. Z/L. The correlation results show that all the stagnation point Nusselt numbers at the same Reynolds number can collapse approximately into a single curve, and these correlations are very successful. Similar kinds of correlations have also been obtained for both the average Nusselt number and the local Nusselt number.