Sub-Atmospheric Pressure, Subcooled, Flow Boiling of Water on Screen Laminate Enhanced Surfaces

Subcooled flow boiling experiments with water at 0.2atm pressure assess the utility of fine filament screen-laminate enhanced surfaces as high performance boiling surfaces. Experiments are conducted on vertically oriented, multi-layer copper laminates in distilled water. The channel Reynolds number is varied from 2,000 to 20,000; and, subcooling ranges from 2K to 35K. Boiling performance is documented for ten different surfaces having pore hydraulic diameters ranging from 39μm to 105μm, and surface area enhancement ratios ranging from 5 to 37. Heat flux of up to 453W/cm² is achieved at 35K subcooling at a channel Reynolds number of 6,000, which represents a 3.5-fold increase in Critical Heat Flux (CHF) over that of saturated pool boiling on the same surface. Results show that CHF is strongly correlated with subcooling; and the effect of subcooling is more pronounced as flow intensity is increased. It is found that CHF enhancement due to subcooling and flow intensity is intrinsically linked to the surface area enhancement ratio, which has an optimum that depends on the degree of subcooling. High speed video imagery (1200fps) and long range microscopy are use to document bubble dynamics. Boiling mechanisms inherent to subcooling, enhanced surface geometry, and CHF are discussed.