Thermal Wake of a Single Rising Air Bubble in a Large Body of Stagnant Liquid

A computational effort was undertaken to study the thermal field behind a slowly rising solitary air bubble. Starting from rest, the bubble moves upward in water due to buoyancy force in the gravitational field and induces both internal and external motion. The bubble, being colder than the surrounding water, is heated by water. The upward motion deforms the shape of the bubble and generates a convective heat transfer process. Variation of temperature at the gas-liquid interface causes a local variation of surface tension. Although the problems of this type have been generally treated by the axisymmetric assumption, the present work employs a three-dimensional model that captures the azimuthal variation of flow parameters. High-speed photography was employed to visualize the bubble evolution from the onset until the bubble reached a certain velocity. The computations were performed using the finite-volume and Volume of Fluid (VOF) techniques. The shape and evolution of the bubble as predicted by the computations are compared with those captured on the high-speed photographs. The computations revealed details of the pressure and temperature fields inside and outside the bubble. They also indicated the thermal field in the wake region behind the bubble.