2019 Fiscal Year Annual Research Report
Development on efficient miniature flat heat pipes for high power electronic cooling
| Project/Area Number |
18F18057
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| Research Institution | The University of Tokyo |
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Principal Investigator |
党 超鋲 東京大学, 大学院新領域創成科学研究科, 准教授 (30401227)
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| Co-Investigator(Kenkyū-buntansha) |
HONG SIHUI 東京大学, 新領域創成科学研究科, 外国人特別研究員
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| Project Period (FY) |
2018-07-25 – 2021-03-31
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| Keywords | Flow boiling / Expanding minichannel / Liquid replenishment / Flow instability / Microchannel heat sink |
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| Outline of Annual Research Achievements |
In the resent work, a 3D inlet distributor employing copper foam is proposed as an extra liquid feeding path to facilitate continuous liquid wetting of the boiling surface and improve the heat transfer performance. A physical heat transfer model accounting for the differences in microchannel void fraction and liquid film thickness caused by the copper foam layer (CFL) has been proposed to describe the working mechanism. The validity of the proposed 3D inlet distributor in heat transfer enhancement was verified using a series of flow boiling tests, employing deionized water as the working fluid. It was found that the local overheating of the microchannel heat sink was demonstrably reduced for all the heat flux values (q) in the tests after adopting the CFL, with a maximum reduction of 14 K at q = 397.6 kW/m2, where local dry-out was successfully inhibited. The heat transfer coefficient of the microchannel heat sink with the CFL was improved by approximately 1.7 times compared to the case without the CFL and could be maintained at 41 kW/m2K during elongated bubble flow and annular flow patterns. In addition, the proposed distributor was capable to resist gravity and long-term severe boiling, thus achieving superior and reliable performance under various orientations as well as during long operating hours.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
we have demonstrated by adopting expanding channel with radial arrangement can significantly suppress the back flow and enhance the heat transfer by at the largest 10 times. this concept provide superior performance compared to conventional microchannel two phase cooling unit especially at low inlet velocity and two phase inlet conditions. In order to apply this concept to larger electronic equipment and overcome the effect of gravity, we proposed a liquid replenish structure to the downstream of the channel where dryout is likely to occur.The proposed 3D inlet distributor employing copper foam has been validated by experiments and heat transfer performance was found increased by 1.7 times. further more, a theoretical model has been proposed to explained the working principle of the 3D inlet distributor.
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| Strategy for Future Research Activity |
In the recent future, the bubble dynamics and fluid mechanics induced by expanding microchannels are expected to investigate to help understand the mechanism of heat transfer improvement of this kind of surface/structure. Some research schemes are proposed.
1.Design and establish a pool-boiling experimental set-up. Verify the rationality of the experimental set-up and be ready for pool boiling test.
2.Related pool-boiling experiment will be conducted. The pool boiling curves as well as the corresponding bubble dynamics on different microchannels will be recorded for comparison. This part of work aims to capture the active liquid supply motion induced by the bubble elongation, and to give the quantitative analysis on the structure effect.
3.Besides, we plan to use metal foam as a “resistance” for vapor escape and strength the vapor-liquid separation for the boiling surface. The effect of the thickness, pore size, porosity and wettability of metal foam on the heat transfer performance and bubbly behaviors will be examined.
4.Moreover, Series of pool boiling test will be conducted with different working fluid to understand the effect of the surface tension as well as density difference between liquid and vapor on the heat transfer improvement. As the active liquid supply motion depends on the bubble elongation which is closely related with the fluid properties, the efficiency of the expanding channel in heat transfer enhancement for low surface tension fluid will be analyzed and discussed in tail.
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