2018 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 / Cut-off structure / Flow instability |
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| Outline of Annual Research Achievements |
A type of rectangular radial expanding minichannel heat sink (REMHS) was proposed. With visualization experiments, we investigated the effects of cut-off and gap structures on flow boiling characteristics in REMHS. The REMHS with cut-off structures maintained a high heat transfer performance with the increase of xout. At xout = 0.39, the superheating degree of wall temperature was 14 K, heat transfer coefficient reached 19 kW/m2K, which was 2 times that of the REMHS without cut-off structures. The gap structure formed vapor-liquid separation in REMHS and decreased the oscillation of wall temperature. The pressure drop characteristic curve in REMHS presented a 2-time polynomial feature and reached the maximum at a low xout. We further investigated the effect of structural parameters (inlet diameter, channel entrance and expanding ratio) on the flow boiling characteristics of two circular REMHS. The wall temperature displayed symmetrically, with a temperature deviation less than 1.3 K. Reverse flow in REMHS-2 was more aggravated, local dry-patch occurred at low xout. As xout increased from 0.25 to 0.52, heat transfer coefficient of REMHS-1 increased from 25.4 to 28.2 kW/m2K, and that of REMHS-2 decreased from 23.3 to 21.2 kW/m2K. The spontaneous deceleration in REMHS resulted in a thinner liquid film layer, the heat transfer coefficient of REMHS varied much flatter with xout or m than that in straight channel. Two-phase flow inlet is also allowed for REMHS.
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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
According to our proposal, the first stage is to comprehend the effect of structural parameters on the flow boiling heat transfer performance of cooling devices. Our investigation basically followed the research planning. In addition, related models for heat transfer coefficient and pressure drop are undergoing on the basis of our experimental results. For the models in heat transfer, the effect of liquid film evaporation will be considered and quantified. For the model in pressure drop, the friction variation and acceleration with the expanding cross sectional area will be discussed in detail. The progress is shown as below:
1) July-September, 2018: Rectangular REMHS design, manufacturing, and experimental loop establishment.
2) October-December, 2018: Testing on rectangular REMHS.
3) January, 2019: Circular REMHS design, manufacturing, and experimental loop establishment.
4) February-April, 2019: Testing on the circular REMHS.
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| Strategy for Future Research Activity |
According to the research progress, we will further discuss the validity of different connection modes for the proposed REMHS to solve the multi-heat source cooling issue. The related experiments are going to be conducted under the similar operating conditions as that for single REMHS. The two-phase inlet condition is expected to take full advantages of the vertical entrance and radial expanding channels, which can mitigate the flow instability and improve the heat transfer capability of REMHS. It is believed the two-phase flow inlet can realize a superior heat transfer coefficient under large vapor quality condition. Besides, to prevent liquid film breakage in REMHS, a capillary layer will be added to realize “liquid-supply” by spraying subcooled liquid spontaneously. The adding of capillary layer enables further enhancement in heat transfer by increasing steady saturated flow boiling region. The optimization of capillary layer, including porosity, pore size, thickness of capillary layer and wetting property will be conducted.
The next progress is planned as below:
1) May-July, 2019: Testing on the effect of connection modes.
2) August-October, 2019: Circular REMHS with capillary layer design, manufacturing, and experimental loop establishment.
3) November-December, 2019: Testing on proposed test section.
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Research Products
(4 results)
