Vapor bubble departure in subcooled flow boiling

An experimental and analytical study was performed on the behavior of a typical vapor bubble growing on a vertical heated surface. Experimental data were obtained for subcooled flow at low pressure (1-3 bar) and low flow rates. The effects of subcooling, heat flux, flow rate and pressure on bubble size and shape were investigated systematically using high speed photography. Flow visualization studies have revealed that bubbles attain a different shape than that typically assumed. Therefore, an ellipsoidal rather than a spherical model has been developed to describe the bubble dynamics. The results of the present study as well as available data compare well with the model predictions. Particular attention is given to forces acting perpendicular to the heated surface that lead to the ejection of the bubble.