Fabrication of a Rib-Roughened Thermal Chip by MEMS Techniques and Measurement of Free Micro Jet Flow and Impingement Cooling Heat Transfer

• Main Authors: Chin-Jian Chang, 張欽荐
• Other Authors: Chie Gau
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/08427992077337065238

碩士 === 國立成功大學 === 航空太空工程學系專班 === 92 === 　　Experiments are performed to study the structure of a free micro-jet flow and micro-jet impingement cooling heat transfer over a thermal chip. In the current work, the thermal chip made was flat. The rib-roughened thermal chip was also made by etching the Si(100) wafer with TMAH. However, due to limitation of current thesis, the impingement cooling experiments over a rib-roughened wall were not made, but are ready for further studies. 　　For the micro-jet impingement cooling experiments, the local Nussult numbers distribution along the thermal chip were measured for the Reynolds number varying from 16 to 640, and the nozzle-to-spacings ratio from 4 to 1600. In addition, different size of nozzles, i.e. 50μm, 100μm, 200μm were used to assure different structures of micro-jet impinging on the wall. The effect of micro-jet impingement cooling study different width of nozzles. It is found that the location for the occurrence of maximum stagnation point Nusselt number decreases with increasing Reynolds number. This is attributed to the decrease of the breakdown length of the micro jet. The maximum stagnation point Nusselt number is expected to occur at the location where jet breaks down. A correlation of the location for the maximum stagnation point Nusselt number in terms of Reynolds numbers can be obtained as (Z/B)max = 24209/Re. 　　For the free micro-jet flow experiments, both flow visualization and velocity distribution measurements using hot wire anemometer were made. There are no coherence structures of vortex formation in the shear layer as appeared in the large-scale jet. It appears that even with large gradient of velocity in the shear layer, the most unstable wave in the shear layer is too weak to have enough energy to roll up into ring vortices for the micro-scale jet. However, the micro-jet has more enough energy in direction of centerline. So, the centerline velocity of micro-jet are highly more then similarity solution. 　　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.