Growth and collapse of vapour bubbles in convective subcooled boiling of water

• Main Author: Farajisarir, Davood
• Language: English
• Published: 2008
• Online Access: http://hdl.handle.net/2429/1358

The growth and collapse of vapour bubbles during convective subcooled nucleate boiling of water in an internally heated annular test section was visualized using the high speed filming technique. The experiments were performed at atmospheric pressure, mean flow velocities of 0.08-0.8 m/s, liquid bulk subcooling of 10-60 °C and heat fluxes of 0.1-1.2 MW/m². High speed photographic results showed that bubbles grew to a maximum radius while sliding on the heated surface; condensed slowly while still attached to the heated surface; and ejected into the flow with further condensation. The bubble volume, displacement of bubble centroid parallel and normal to the heating surface, and change in the bubble maximum and minimum diameters were evaluated during the bubble lifetime. The effects of heat flux, liquid bulk subcooling and mean flow velocity on maximum bubble radius, growth time, and condensation time were investigated. At low subcoolings, an increase in the heat flux resulted in a decrease in the maximum bubble radius and growth time. At high subcoolings, the maximum bubble radius and growth time were independent of the heat flux. The effect of mean flow velocity on bubble parameters was negligible in the range of this study. Correlations are proposed for the maximum bubble radius, growth time, condensation time, and growth and collapse rates.