Bubble-laden thermals in supersaturated water

Abstract

Bubble-laden thermals provide a formidable gas transport mechanism responsible, for instance, for the explosive foaming-up process during the beer tapping prank, or the infamous gas eruption of Lake Nyos in 1986. In this work we investigate experimentally the growth and motion of laser-induced turbulent thermals in a carbonated water solution with surfactants. One of the novelties of this study is that we are able to quantify with high temporal resolution the rate at which the gas volume contained in the bubbles grows. After an initial transient stage, the gas bubble and entrained liquid volumes of the thermal both grow as a cubic power of time. The buoyancy generation rate is well explained by the mass transfer scaling expected for individual bubbles. In contrast, the thermal rise velocity does not adhere to any particular scaling law. These facts lie in qualitative agreement with a phenomenological model, based on classical models for turbulent thermals, that takes into account buoyancy generation.