Boiling Under Hele Shaw Flow Conditions: The Occurrence of Viscous Fingering

Abstract

Boiling and bubble dynamics were experimentally investigated in a HeleShaw flow cell using pure water at atmospheric pressure as the working fluid. The resulting vapor bubble shapes were recorded by means of a highspeed camera for several plate spacings and heating power levels. It was found that viscous fingering phenomena of vapor bubbles occurred only under very special boiling conditions and cell parameters. The evaporation front velocity was identified as a major parameter for the onset of viscous fingering. The observed basic viscous fingering dynamics was in reasonable agreement with theoretical analyses. In addition to that classical viscous large fingering, smallscale evaporation instability was observed leading to microscopic roughening of accelerating evaporation fronts. This instability might be explicitly related to evaporative heat and mass transfer effects across the fastmoving phase interface.