| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 92 === The objective of this work is to grow well-alignment and high degree of graphitization of CNTs at ultra low temperature. In the present work here, we have succeeded in varying such parameters as the Ni thickness, the MW power, the growth time and the pretreatment time to synthesize almost none amorphous carbon of CNTs. Furthermore, we have also succeeded in synthesizing well-alignment CNTs at ultra low temperature, i.e. 450℃or 260℃. The Raman optical spectrum intensity of this multi-wall carbon nanotubes were grown at 260℃is 0.2356. Another important property of CNTs is the electron-field-emission performance. It is the turn-on electric field is 2.849V/μm. As the applied electric field is 5V/μm, we can obtain an emission electric current density approximately 0.2mA/cm2.
This second objective of this study is to perform the micro-jet impingement cooling heat transfer over the rib-roughened thermal chip. The rib-roughened thermal chip was made by wet etching the Si (100) wafer .Until now, however, no one was reported the micro-jet impingement cooling heat transfer over the rib-roughened made by Si on a thermal chip.
For the micro-jet impingement cooling experiments, the local Nusselt numbers distribution along the rib-roughened thermal chip were measured for the Reynolds number varying from 16 to 640, and the nozzle-to-spacing ratio from 4 to 3200. In addition, different size of nozzles, i.e. 25μm, 50μm, 100μm was used to ensure different structures of micro-jet impinging on the wall. The effect of micro-jet impingement cooling varies with the width of the 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 the jet breaks down. A correlation for the location where the maximum stagnation point Nusselt number occurs with the Reynolds numbers can be obtained as (Z/B)max = 27966/Re.
An attempt was first made to correlate the stagnation point Nusselt number in terms of relevant no dimensional parameters such as the Reynolds number and Z/B. This is done by first normalizing Z/B by dividing L, i.e. Z/BL. 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 numbers.
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