With the growing power dissipation and more densely packed circuits, the issue of efficient thermal management has become crucial. The safe and reliable operations of microchips have a requirement on a junction temperature below 85??C. In order to meet the heat dissipation requirement at the level of 1 MW m???? of the next generation microchips, a new cooling approach has been proposed by combining the merits from forced convection in the microchannel and the synthetic jet impingements. A parametric study has been carried out on the operating conditions on the synthetic jet actuator, these parameters including: the frequency of the diaphragm in the actuator, the jet outlet velocity both in magnitude and the wave shape as well as the pressure difference between the channel two ends. It was found that these parameters have combined effect on the flow structure as well as the heat transfer rate in the microchannel. When the average jet velocity was at 2.36 ms??ยน(Rej= 130), with a fixed pressure difference at 750 Pa, the maximum temperature in the silicon wafer has been reduced to about 343 K at both 560 and 1120 Hz, which was 2 K lower than when 280 Hz was used. However when the average jet velocity was increased by 50 %, the optimal heat transfer then occurred at 1120 Hz, the maximum temperature was reduced to 337 K, with 4 K and 5K difference of 280 and 560 Hz, respectively. Furthermore when the average jet velocity was doubled from Rej= 130, the frequency at 280 Hz achieved the lowest maximum temperature in the wafer at 336 K that was 5 K and 3 K lower than 560 Hz and 1120 Hz. The flow temperature in the actuator is an important factor which affects the heat transfer in the microchannel. In order to lower the cavity temperature and avoid the ingestion of the already mixed flow, the time portion of the ingestion and ejection phases has been altered, by reducing the ejection time and increasing the ingestion time. However this approach did not show any significant effect in the heat transfer process or decreasing the flow temperature in the cavity. However in a later study by increasing the pressure difference across the channel, the flow temperature in the cavity has been substantially reduced and the heat transfer in the channel changed significantly according to the flow structure. It was found that the high pressure in the channel could deliver the vortical structure to the hotter part of the wafer thus decreasing the maximum temperature in the silicon effectively, especially when high jet velocity was used. When high jet velocity has been used, irregular variation of the flow was found The unrepeatable feature of the flow is related to the frequency, jet velocity as well as the channel pressure difference.
| Identifer | oai:union.ndltd.org:ADTP/258686 |
| Date | January 2009 |
| Creators | Li, Dan, Mechanical & Manufacturing Engineering, Faculty of Engineering, UNSW |
| Publisher | Awarded by:University of New South Wales. Mechanical & Manufacturing Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Li Dan., http://unsworks.unsw.edu.au/copyright |
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