A benign method of generating a surface microstructure that provides pool boiling heat transfer enhancement is introduced. Pool boiling heat transfer results from an enhanced, horizontally oriented, rectangular surface immersed in saturated FC-72, indicate up to an 85 percent decrease in incipient superheat, a 70 to 80 percent reduction in nucleate boiling superheats, and a ∼ 109 percent increase in the critical heat flux (CHF = 30 W/cm2), beyond that of the nonpainted reference surface. For higher heat flux conditions (19 to 30 W/cm2), localized dryout results in increased wall superheats (8 to 48°C). The enhanced surface heat transfer coefficients are four times higher than those from the reference surface and similar to those from the Union Carbide High Flux surface. Photographs that identify differences in bubble size and departure characteristics between the painted and reference surfaces are presented.

The effects of surface treatments and " gassy-subcooling " on pool boiling heat transfer are quantified by testing both smooth and treated surfaces at gassy-subcooling levels from O°C to 40°C (1 arm) and 40°C to 85°C (3 atm). Incipient and nucleate boiling wall superheats decrease over this range of gassy-subcooling. At gassysubcooling levels greater than 20°C, the boiling curves for the smooth surface indicate two distinct regions governed by different heat transfer mechanisms, one in which the boiling process is influenced by the presence of dissolved gas, the other by boiling of the pure liquid. The critical heat flux ( CHF ) for each surface continually increases with increased levels of gassy-subcooling and the CHF sensitivity to gassy-subcooling is higher for the treated surface~ The CHF increase due to combined surface treatment and gassy-subcooling (85°C) is ~400 percent (78 W/cm2).

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Abstruct-Two benign methods of generating surface micro-I. INTRODUCTIONstructures, "spraying" and "painting," provide pool boiling heat transfer enhancement. The methods do not require the target surface to be exposed to high stress environments, making them applicable to electronic component surfaces. The painted surface micro-structures are applied to a rectangular, horizontally oriented surface, and provide up to a 85% reduction in incipient superheat, between a 70 and 80% reduction in nucleate boiling superheats, and as much as a 100% increase in the maximum heat flux (critical heat flux-CHF), beyond that of the nontreated reference surface. The surface micro-structures are also applied to a silicon test chip and tested at saturated and sub-cooled (45°C) conditions using FC-72. At sub-cooled conditions, heat dissipation rates of 100 W/cm2 were provided at junction temperatures of 85"C, and the highest CHF observed was 159 W/cm', 224% higher than that from the untreated chip surface at saturated conditions. CHF k L P,,t R Rtcond Tbulk Tcrit Tref Tt c TI,