| Summary: | This report summarizes work carried out during the first two years of a research program sponsored by IBM Corporation. This study has elucidated a number of the heat-transfer characteristics of several fluorochemicals which have potential application as coolants for high power density computer components. Single-phase heat-transfer coefficients have been determined for Freon-113 and FC-78 flowing in a rectangular channel with one of the wide sides heated. Heat-transfer coefficients for the short channels are significantly higher than those predicted by conventional correlations due to entrance effects and superimposed free convection. Uncertainties as to the actual values of certain thermophysical properties introduce corresponding uncertainty in correlation. Subcooled flow boiling data were taken with the rectangular channel for a wide variety of fluid-surface combinations, and over a wide range of flow conditions. These data should facilitate a close estimate of surface temperatures in actual systems. Data taken with an annular test section delineated hysteresis effects which were tentatively identified in the rectangular channel tests. Pool boiling tests indicated large temperature overshoots in the boiling curve with Freon-113. It was found that conventional correlations do not adequately describe critical heat flux data for horizontal circular heaters. The critical heat flux increases as diameter decreases, and increases as the wall thickness increases. The observed hysteresis effects in pool and flow boiling were examined in detail. It is suggested that the phenomenon of temperature overshoot hysteresis is due to two causes: a) the existence of metastable bubbles which are triggered only at sufficiently high disturbance level, and b) the deactivation of larger nucleation sites by displacing the vapor by liquid during subcooling.
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