A Flow Boiling Heat Transfer Investigation of FC-72 in a Microtube Using Liquid Crystal Thermography

Abstract

This paper presents experimental measurements of boiling heat transfer in a 1.067 mm inner diameter tube, using liquid crystal thermography for wall temperature measurement. The study was motivated by the two-phase microchannel pumped cooling loop, a recent technology proposed for thermal management of tomorrow's high-end electronics. The working fluid was FC-72, which is a dielectric coolant and measurements were obtained in a closed loop test facility. A unique flow boiling onset was observed whereby a large wall temperature gradient travels along the tube. During flow boiling conditions, wall temperature fluctuations have been observed. The use of a thermographic technique has added insight into the flow boiling characteristics and acts as a partial flow visualization method. Local heat transfer coefficients are presented and compared with correlations for both macro- and microchannels. The heat transfer coefficient is found to be influenced by the heat flux at a lower mass flux but only mildly at a higher mass flux.