Characteristics of pool boiling heat transfer in the vicinity of the critical heat flux point. (The relations between bubble motion and heat flux fluctuation)

In order to study the mechanism of critical heat flux of pool boiling, measurement of heat flux fluctuation and high speed photographic observation were carried out simultaneously on a constant temperature surface heated by electrically controlled Joule heating, in the vicinity of a critical heat flux point. They revealed the following : (1) when the surface is covered by a coalesced bubble, heat flux begins to increase because evaporation is enhanced ; (2) heat flux begins to decrease either while the surface is covered by a coalesced bubble due to dryout of the liquid on the surface, or just after nucleation begins under the rising bubble due to a relatively low heat transfer rate of nucleation ; and (3) heat applied from the time the surface is covered by a bubble until the time heat flux begins to ducrease does not vary widely and corresponds to latent heat of liquid about 11 -μm thick.