A study of bubble ebullition in forced-convective subcooled nucleate boiling at low pressure

Abstract

An investigation of forced-convective subcooled nucleate boiling was carried out using high speed photography. Experiments were performed using a vertical circular annulus at atmospheric pressure, for mean flow velocities of 0.08–1.2 m s −1 and subcoolings of 10–60°C. The filmed conditions are defined relative to the onset of nucleate boiling and the onset of significant void. The following observations were made: (i) bubbles do not grow and collapse on the heated wall, but eject into the flow for subcoolings below 60°C; (ii) after the onset of nucleate boiling, bubbles slide away from the nucleation site and later eject into the flow; (iii) bubbles condense while sliding on the wall; and (iv) bubbles generated near the onset of nucleate boiling conditions slide for a distance of up to 50 mm, while for other conditions the total axial distance traversed by the bubbles is less than 2 mm on average. The maximum bubble diameter and condensation time are shown to be influenced by the location relative to the onset of significant void.