The Influence of Subcooling on the Frequency of Bubble Emission in Nucleate Boiling

The experimental results reported in Ibrahim and Judd (1985) in which bubble period first increased and then decreased as subcooling varied over the range 0 ≤ θ_sat ≤ 15° C is interpreted by means of a comprehensive boiling heat transfer model incorporating the contributions of nucleate boiling, natural convection, and micro-layer evaporation components. It is shown that bubble emission frequency varies to accommodate the impressed heat load in the manner described above because changes in subcooling cause the heat flux within the area influenced by the formation and departure of bubbles to change in the opposite sense to the fraction of the surface area within which bubble formation and departure occurs. The mechanism responsible for the nucleation of bubbles at exactly the frequency required at each level of subcooling is the object of continuing research.