Continuing trend of higher packaging density and the increasing device heat dissipation rate of electronic control unit (ECU) for automobiles requires the further advancement of ECU cooling technology. One of the major heat transfer paths from the ECU to the ambient is the contact between the ECU enclosure and the metal chassis where the ECU is attached to the body of the vehicle. Bolted attachment however cause surface deformation of the ECU enclosure that deteriorate the heat transfer capability. Although the deformation-caused surface waviness is apparently responsible for the increase of thermal contact resistance (TCR), vast majority of the conventional TCR works have focused only on the effect of surface roughness, including the pioneering works done by the Japanese researchers, Tachibana and Sanokawa. Their Tachibana-Sanokawa Equation of TCR considers various surface roughness parameters, it however cannot handle the waviness. This work mainly focuses on the effect of the strain caused by the bolted joint and the resulting or designed waviness on the TCR. Elasticity analysis of bolt-jointed two test plate specimens shows the deformation characteristics. Then, the pressure distribution between the ECU enclosure and metal surfaces is visualized in order to confirm the effect of designed waviness on ECU enclosure surface. Thermal experiment is then conducted to quantitatively show the significance of the designed waviness. The results discussed in the present work is expected to have impact not only to the ECU cooling but to the wide range of industrial application.

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Possibility of enhancement of boiling heat transfer under subatmospheric pressure is examined experimentally. Considering the application for CPU cooling by phase change, pressure is cited as 15kPa. Effect of surface size on heat transfer performance of pyramid type surfaces is especially examined. By increasing the heat transfer surface size from 10mm square to 25mm square, experimental heat transfer performance of smooth surface becomes to agree well with Labountzov’s correlation. Furthermore, heat transfer performance of pyramid type surface increased with increment of surface size, and optimum pitch changed from 1.0mm to 2.5mm. Increase ratio of heat transfer coefficient of 25mm square pyramid types from smooth surface is also larger than that of 10mm square pyramid types.

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Jet impingement quenching as one of the most efficient cooling techniques has many practical applications. When a liquid jet impinges on a hot surface beyond the homogeneous nucleation temperature, a stable wetted area remains on a small stagnant region at an earlier time. Then the wetting area starts propagating outside at a particular velocity over the hot surface after a specific resident time. In the present study, subcooled water jet quenching experiments on a hot nickel disk were conducted to elucidate transient boiling transition between film and nucleate boiling regimes on the wetting front, which was the tip of the wetted region. A local transient heat transfer was measured for different jet velocities, jet subcoolings, and initial temperatures with a fast response thin-film thermocouple. Though the transient local boiling heat transfer around the wetting front fluctuated highly and irregularly due to reputations of local wet and dry at a dominant period of about 1 ms, time-averaged heat transfer characteristics agreed fairly well with the existing correlations for steady-state pool boiling heat transfer, critical heat flux and single-phase convection.

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In our previous study, interfacial tension during microwave irradiation was measured, and interfacial modification for surfactant desorption was discovered through the quick response of the tension. Although higher output is necessary to maximise interfacial modification, continuous thermal energy supply by microwave absorption causes boiling from interface. Therefore, we thought that it is necessary to disperse the energy during the interval by the pulse microwave irradiation. On the other hand, the surfactant is re-adsorbed during the interval. In this study, the mechanism of surfactant desorption caused by microwave local heating was discussed by means of our dimensionless number proposed as index of the energy concentration.

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