MICROLAYER AND BUBBLE GROWTH IN NUCLEATE POOL BOILING

A theory is presented to determine the rate of growth of a vapour bubble growing from a heated wall in a liquid which is near to saturation temperature. The theory depends on approximate assumptions derived from experiments in which thin liquid layers (microlayers) were observed to occur under such bubbles, and in which the evaporation of the microlayers contributed significantly to the growth of the bubbles. To simplify the analysis it is based on assumptions representative of more extreme situations in which the microlayer predominates, extremes which have not previously been explored. The predictions of the analysis bear some relation (±25 per cent) to the results of experiments with various fluids under conditions for which the assumptions are approximately valid. These predictions, with associated limitations on the ranges of validity of the assumptions, together indicate conditions under which microlayers may be expected to have significant effects on bubble growth. They also have implications for bubble departure size, at standard and reduced gravity. Water, organic liquids, cryogens and metallic fluids are discussed. The theory is extended to include boiling with liquid bulk temperature differing significantly from saturation temperature. © 1969.