NUCLEATE POOL BOILING OF WATER ON A HEATER OF THE SIZE OF A CAPILLARY LENGTH

Nucleate pool boiling of saturated water at one atmosphere pressure was investigated on a horizontal circular surface of diameter 2.7 mm. For such a surface aside from the contact angle of the surface itself, the wettability of the surrounding surface is found to have a significant effect on both the dependence of nucleate boiling heat flux on wall superheat as well as the critical heat flux. For heated surface with a contact angle of 90 degrees, with a hydrophobic surface surrounding it, the nucleate boiling heat transfer and critical heat flux are much lower than for the hydrophilic surrounding surface. However, when the heater surface is well wetting, contact angle less than 50 degrees, there was significant improvement that could only be seen with hydrophilic surrounding. Nucleate boiling heat transfer and critical heat flux data are found to correlate with bubble departure volume and frequency of the bubble release.