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12 results on '"Wada, Mizuki"'

4. Feasibility study of two-phase immersion cooling in closed electronic device

Author

Wada Mizuki, Mahiro Hachiya, Arihiro Matsunaga, Masaki Chiba, Minoru Yoshikawa, and Kunihiko Ishihara

Subjects
Materials science, Phosphor bronze, 020209 energy, Thermal resistance, 020208 electrical & electronic engineering, Mechanical engineering, 02 engineering and technology, Heat sink, Thermal conduction, Thermal diffusivity, Coil spring, Coolant, Heat transfer, 0202 electrical engineering, electronic engineering, information engineering
Abstract

Feasibility of two-phase immersion cooling in a closed electronic device such as a microwave transmitter is experimentally investigated. Two-phase immersion cooling directly cools multiple heat sources with various shapes which enables simple and flexible thermal design by fulfilling the existing electronic device with a coolant. The challenge is to reduce internal thermal resistance from heat sources to the chassis surface by effective thermal diffusion induced by two-phase immersion. The study covers selection of coolant and effect of coolant filling ratio. Then heat dissipation performance by single and multiple heat sources as well as enhancement by two-phase immersion with conduction materials are experimentally tested. Leaf spring and coil spring, both made of phosphor bronze, are used as the conduction materials and compared with rigid copper block in two-phase immersion. Experiment setup contains a vertical heating plate and an outer wall with heatsink separated by a gap space. Thermal resistance of basic two-phase immersion and enhancement by conduction materials are compared to provide design guideline for two-phase immersion application in a closed device.

Published
2017

6. Phase change cooling with evaporative condenser at data centers

Author

Sato Masanori, Arihiro Matsunaga, Minoru Yoshikawa, and Wada Mizuki

Subjects
010504 meteorology & atmospheric sciences, Nuclear engineering, Plate heat exchanger, Thermodynamics, 010501 environmental sciences, Heat sink, 01 natural sciences, Heat recovery ventilation, Heat transfer, Heat spreader, Environmental science, Plate fin heat exchanger, Condenser (heat transfer), 0105 earth and related environmental sciences, Shell and tube heat exchanger
Abstract

Chiller-less data centers are energy efficient but only available in cold climate regions. This is due to high thermal resistance between heat sink and ultimate sink (ambient air) and heat dissipation rate relies on environment temperature. The purpose of this study is to extend availability of chillerless data center with a rack rear-door heat exchanger in warm climate regions. Evaporative condensers with natural/forced circulation cooling system by phase change heat transfer were experimentally studied to reduce thermal resistance at the condenser. Furthermore, impact of heat exchanger configuration and effect of atomized water spray were studied. Experiment verified that thermal resistance reduction in the external side of the heat exchanger by water vaporization failed to appear when horizontal heat exchanger configuration was used. Approximately 40% reduction of thermal resistance of condenser was observed on the data center test facility by spray of atomized water particles, produced by pneumatic spray nozzle, on the vertical heat exchanger at wet bulb temperature of 15°C. The results suggest that energy savings can be achieved by the appropriate evaporative condenser usage that reduces running cost of data centers in warm climate regions.

Published
2016

8. Amplification and reversal of Knudsen force by thermoelectric heating

Author

O'Neill, William J, Wada, Mizuki, Strongrich, Andrew D, Cofer, Anthony, Alexeenko, Alina A, O'Neill, William J, Wada, Mizuki, Strongrich, Andrew D, Cofer, Anthony, and Alexeenko, Alina A

Abstract

We show that the Knudsen thermal force generated by a thermally-induced flow over a heated beam near a colder wall could be amplified significantly by thermoelectric heating. Bidirectional actuation is achieved by switching the polarity of the thermoelectric device bias voltage. The measurements of the resulting thermal forces at different rarefaction regimes, realized by changing geometry and gas pressure, are done using torsional microbalance. The repulsive or attractive forces between a thermoelectrically heated or cooled plate and a substrate are shown to be up to an order of magnitude larger than for previously studied configurations and heating methods due to favorable coupling of two thermal gradients. The amplification and reversal of the Knudsen force is confirmed by numerical solution of the Boltzmann-ESBGK kinetic modelequation. Because of the favorable scaling with decreasing system size, the Knudsen force with thermoelectric heating offers a novel actuation and sensing mechanism for nano/microsystems.

Published
2014

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