In the wake of bubbles: Velocity Field Measurement by PIV Technique

Abstract

In this paper, the PIV (Particle Image Velocimetry) non-intrusive technique is proposed to calculate the velocity field in the wake of a single bubble rising with a rectilinear path in a quiescent liquid. The aim of this study is to find a general equation which describes the velocity of the flow in a bubble wake. Then, it will be possible to find the term relative to the convective mass transfer around the bubble and, at last, the total mass transfer around it. The set-up tracks the velocity field evolution along the bubble wake for a parallel plane to the bubble path. A spherical bubble is created through a capillary thanks to the constant pressure which applies a syringe pushed by a programmable syringe pump, regulating in this way the advance speed of the injected air. The bubble rises through a glass column containing different solutions, thus presenting different viscosity and Re conditions. Each of these solutions is seeded with silvered tracer particles whose movement allows following the flow velocity field thanks to the PIV method. A high speed camera is located far from the column in order to record the bubble position, size and velocity. This camera is also synchronized with the laser flash by a synchronizer processor. All the experiments have been carried out with bubbles ranging from 0.75 to 3 mm and with 6 hydrodynamic conditions (1 < Re < 125).