Effect of Pressure, Subcooling, and Dissolved Gas on Pool Boiling Heat Transfer From Microporous Surfaces in FC-72

Abstract

The present research is an experimental study of the effects of pressure, subcooling, and non-condensable gas (air) on the pool nucleate boiling heat transfer performance of a microporous enhanced and a plain (machine-roughened) reference surface. The test surfaces, 1-cm2 flat copper blocks in the horizontal, upward facing orientation, were immersed in FC-72. The test conditions included an absolute pressure range of 30–150 kPa, a liquid subcooling range of 0 (saturation) to 50 K, and both gas-saturated and pure subcooling conditions. Effects of these parameters on nucleate boiling and critical heat flux (CHF) were investigated. Results showed that, in general, the effects of pressure and subcooling on both nucleate boiling and CHF were consistent with the prevailing trends in the literature. For the present heater geometry, the effects of dissolved gas on the boiling performance were generally small, however, as the dissolved gas content increased (through either increased pressure or subcooling) more of the nucleate boiling curve was affected (enhanced). The enhancement of CHF from increased liquid subcooling was greater for the microporous surface than the plain surface. Correlations for both nucleate boiling and CHF were also presented.