Characterization of net coolant flow rate to copper boiling surfaces using two-phase particle image Velocimetry and dielectric fluid

Abstract

Particle Image Velocimetry (PIV) has been widely used in fluid mechanics for various single and two-phase flow visualization studies. Using PIV, the net coolant flow rate required for quenching a copper circular heated surface under high heat flux pool boiling applications was quantified. The flow rate was calculated using a control surface analysis of all the periphery vectors surrounding the pool boiling activity. The vectors were deconstructed into their relevant Cartesian components using a custom Matlab code. The acquired data may be useful for empirical modeling of many practical high-performance electronic systems including thermosiphons and multi-component liquid immersion cooled servers. Boiling heat transfer fluxes ranging from 5.5 W/cm2 to 11 W/cm2 yielded quenching fluid flow rate requirements ranging from 1.7 g/s to 93.6 g/s. The highest heat flux tested, 11 W/cm2 is near the Critical Heat Flux (CHF) for the PF-5060 working fluid with a resulting maximum heat transfer coefficient of 8.8 kW/(m2K). With subcooled boiling conditions, it was found that as little as 2.5 °C reduction in pool temperature below the saturation point resulted in a 42% reduction in required coolant flow rate. A further reduction in the cooling flow rate requirement, 87% below the saturated pool condition, was found when the subcooling level was increased to 5 °C. When subcooling is introduced, transient conduction near the microlayer vapor/surface/liquid interface of bubble formation begins to be the dominant heat transfer mechanism.