Growth and collapse of vapor bubbles in subcooled boiling near the region of alternating boiling modes

The growth and collapse of vapor bubbles in subcooled pool boiling of water have been observed using high-speed video. The bubbles have been generated at a single nucleation site on a vertical circular copper surface in the pressure range of 25 kPa less than or equal to p less than or equal to 40 kPa and the subcooling range of 4 K less than or equal to Delta T-sub less than or equal to 40 K. Relative regular alternations between bubbles generated at a single nucleation site and populations of small bubbles occur at subcoolings higher than 25 K. The lower the pressure, the more pronounced are these alternations, which are accompanied by a more or less effective heat transfer and wall temperature fluctuations up to 40 K. The time proportion that each of these different boiling modes contributes to meet the given constant heat flux depends also on the subcooling. The start of the small bubbles' mode always seems to be the result of a rapid collapse of a big initial bubble which causes a secondary nucleation process. Measurements of bubble life cycles are presented. The frequency of bubble generation, time of growth and collapse and extensions of the bubbles are shown to depend on pressure, heat flux and subcooling. The relations of bubble parameters and boiling modes are described.