Bubble Dynamics in Confined Spaces: Effect on Heating Surface

Abstract

A theoretical study of the dynamics of a single vapour bubble growing between two close surfaces is presented. The results show that the existence of a solid wall situated opposite to the heating surface influences the bubble shape and tends to divert its geometry from the spherical to the ellipsoidal one. One also observes a slower growth rate in the direction perpendicular to the surface. Considering the forces responsible for the bubble detachment, it was found that the bubble departure radius and departure time increase when the width of the gap between the two surfaces is reduced. A close look at the mechanism leading to the heating surface “Departure from Nucleate Boiling” (DNB) in confined spaces indicated that the heating surfaces DNB is increased and the local “Critical Heat Flux” (CHF) is considerably reduced. The development of this phenomenon is explained and supported by previous experimental findings. Two transient heat conduction models are used to estimate the local heating surface (hot spot) temperature in the confined dry areas. The results show that, within a few seconds, the hot spot temperature excursion occurs and may lead to local surface damage.