1999 Fiscal Year Final Research Report Summary
An Experimental Study on New Technology of Dynamic Cooling with Jet Impingement
| Project/Area Number |
10450086
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Thermal engineering
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
SUZUKI Kenjiro Kyoto Univ., Fac. Engineering, Professor, 工学研究科, 教授 (00026064)
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| Co-Investigator(Kenkyū-buntansha) |
IWAI Hiroshi Kyoto Univ., Fac. Engineering, Research Assoc., 工学研究科, 助手 (00314229)
NAKABE Kazuyoshi Kyoto Univ., Fac. Engineering, Assoc. Prof., 工学研究科, 助教授 (80164268)
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| Project Period (FY) |
1998 – 1999
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| Keywords | Jet Impingement / Crossflow / Heat Transfer Control / Heat Transfer Measurement / Velocity Measurement |
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| Research Abstract |
Effectiveness of large-scale longitudinal vortices and self-excited oscillation generated by a jet on impingement heat transfer were investigated in order to improve the performance of jet impingement cooling devices. Attention was paid to the following three items; (1) geometrical configurations of jet nozzle, (2) frequencies of the self-excited oscillation, and (3) patterns of vortical structures. The interaction of jets were also investigated together with the development of measuring techniques related to the heat transfer coefficients and flow velocity profiles. LDV and PIV systems were used to measure local velocity fluctuations and cross-sectional velocity vector distributions, respectively. The temperatures of the heat transfer target wall were measured using thermochromic liquid crystal sheets, the color images of which were taken with a CCD camera. Neural network method was applied to transform the color images into the wall temperature distributions. In the case of the jet obliquely discharged into a main flow, a pair of large-scale counter-rotating vortices was clearly visualized in the cross-section illuminated by a laser sheet, which was numerically predicted under similar boundary conditions. Comparison between the conventional vertical impinging jet and the present oblique jet reveals the superiority of the oblique jet to the vertical one. In the case of the self-excited oscillation jet, the patterns of Nusselt number distributions in the stagnation region drastically change under the conditions of relatively small impingement distance. Only small change of the geometric scales of the jet nozzle was required to generate the audible oscillation without any extra energy to the jet. Thus, the excited oscillation was found to have a great influence on the jet impingement heat transfer. Corresponding to the cases most influenced by the oscillation, Strouhal number based on the oscillation frequency was around 0.3.
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