EFFECT OF SURFACE WETTABILITY ON TRANSITION BOILING HEAT TRANSFER FROM A VERTICAL SURFACE
Transition boiling heat transfer from a 6.3 cm wide and 10.3 cm high copper surface is studied experimentally. The experiments are conducted in pool boiling mode using saturated water and Freon-113 at one atmosphere pressure. The wettability of the surface is changed by oxidizing the surface or by depositing a thin coating of flurosilicone sealant. The experiments are conducted in both heating and cooling modes. The transition boiling heat fluxes obtained during heating mode are generally higher than those obtained during cooling mode. The difference between the two diminishes as the surface becomes more wettable or as the contact angle decreases. Using contact angle as a measure of surface wettability, the maximum heat flux is found to decrease with increase in the contact angle. At a contact angle of 107°, the observed steady state maximum heat flux is about 50% of that predicted from the hydrodynamic theory which does not include the surface effect. The transition boiling data including the data for the maximum heat flux are correlated with the contact angle.