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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

An Analysis of the Effect of the Footprint Orientation on the Heat Sink Performance during Flow Boiling in Micro-Scale Channels

Get access (open in a dialog) DOI: 10.1615/IHTC15.fbl.008705
pages 2693-2707

Abstract

This paper describes an experimental study concerning the effect of the footprint orientation on the performance of a microchannels heat sink during flow boiling. The heat sink posses a footprint area of 15x15 mm2 and contains fifty parallel microchannels with cross-sectional dimensions of 100 x 500 µm, and total length of 15 mm. The ?ns between consecutive channels are 200 µm wide. Experiments were performed for R245fa, mass velocities from 400 to 1200 kg/m2s, heat fluxes up to 320 kW/m2, liquid subcooling at the heat sink inlet plenum of 5 and 10°C and saturation pressure of 180 kPa. The heat sink performance was evaluated with its footprint area positioned horizontally (HP), vertically with the microchannels aligned horizontally (VHP) and vertically with upflow through the microchannels (VP). Images of the flow boiling process in the microchannel based heat sink were captured with a high speed camera (3000 frames/s). The excess of superheating for the onset of nucleated boiling was found of the experimental condition. The average heat transfer coefficient was higher for the footprint area positioned horizontally. Heat transfer coefficients up to 33 kW/m2K were obtained. The effect of the footprint orientation on the heat transfer coefficient increases with increasing mass velocity and liquid subcooling. The pressure drop was higher for the heat sink positioned vertically with the microchannels aligned horizontally. Lower pressure drops were obtained for the heat sink positioned vertically and upwards flow. A large bubble concentration was observed in the lower part of the heat sink for higher mass velocity and the configuration VHP. Reverse flows were observed for footprint orientations HP and VHP. Discontinuities in the boiling curve just before the ONB have occurred simultaneously to bubble nucleation at plenum.