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Flow Boiling of Water at Reduced Pressure in Micro Pin-Fin Heat Sink
Keywords: flow boiling, micro pin-fin heat sink, micro channels
Flow boiling is one of the most effective methods to remove heat due to the fact that it can achieve very high heat transfer coefficient with an acceptable wall superheat, compared to single phase flow. The thermal and hydraulic characteristics of flow boiling in micro-channels have been studied extensively in the past decade, as well as its applications in heat removal in high performance electronics. This presentation show studies of flow boiling of reduced pressure water in micro pin-fin heat sink. Five designs of micro pin-fin heat sink are studied, with circular and hydrofoil pin shapes, and also with different pin sizes and pitches. The micro pin-fin heat sinks are micro-fabricated from silicon. Metal heaters and 12 small RTDs are deposited on back side of heat sink for the purpose of supplying power to the micro pin-fin heat sink and local temperature measurements. The micro pin-fin heat sink is attacked to glass cover with epoxy to close the flow passage, and the transparency of glass cover allows flow visualization. A closed flow loop system is used to test the micro pin-fin heat sink. The closed flow loop consists of fluid reservoir of 300mL, gear pump, 7-micron pore size filter, flow meter for flow rate measurement, pre-heater, test section, and temperature controlled condenser. There are totally four points of pressure measurements and six points of temperature measurements in the flow system, including fluid pressure and temperature at the inlet and outlet of heat sink. The micro pin-fin heat sink is electronically connected with PCB by wirebonding, and assembled with a package for mechanical support. The package also has measurement ports, and inlet and outlet fluid pressure and temperature can be measured very locally close to the heat sink. The working fluid is water at reduced pressure to decrease the boiling point and pressure inside the flow loop. Thermal and hydraulic characteristics of different designs of micro pin-fin heat sinks subjected to different heat fluxes and mass fluxes are studied.
Xuefei Han,
Georgia Institute of Technology
Atlanta, GA

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