Features of vapor bubbles evolution at liquid boiling at subatmospheric pressures

Abstract

The article presents the results of an experimental study of the dynamics of vaporization at water boiling at subatmospheric pressures up to 8.8 kPa. The usage of a transparent heater, high-speed video and IR thermography allowed analyzing the effect of pressure on the dynamics of vapor bubbles, the evolution of dry spots as well as the surface superheating corresponding to the onset of boiling. It is shown that the pressure reduction at a given heat flux density leads to a significant increase in the Jacob number at the activation of the nucleation site and the growth rate of vapor bubbles. It has been found that the curve of dry spots growth rate has a nonlinear dependence on the pressure in the range of 8.8-103 kPa. The minimum value of the growth rate of dry spots is observed at a pressure of 42 kPa.