Experiments are reported in which organic liquids underwent pool boiling at low pressure, forming large vapour bubbles on the surface of a heater plate consisting of glass or ceramic. The temperature at the surface of the heater was measured, leading to support for the hypothesis that a thin layer of liquid (the microlayer) forms beneath the vapour bubble. From the experimental observations it is possible to deduce the thickness of the microlayer, which can also be predicted from a simple theory for the hydrodynamics of the formation of the layer. Experiment and theory agree within ±25 per cent for the limited cases available. The rates of growth of the bubbles are shown to be of the same order as the rates of evaporation from the microlayers, which can be expressed in analytic form under certain assumptions. A computer program for bubble growth allowing for the microlayer and other factors has been developed and applied to two bubbles growing under widely different bulk temperatures. The predicted radii are within ±15 per cent of those observed. The relative magnitudes of stresses due to inertia, surface tension, viscosity and gravitation are determined for a typical bubble, and discussed in relation to bubble shape and microlayer formation. It is stressed that these results may not apply to widely different conditions of boiling. © 1969.
