Bubble rise characteristics in oscillating grid turbulence

Abstract To clarify the effects of free stream turbulence and surfactant concentration, a systematic study was carried out using an advanced PIV/Shadowgraphy system. The experiments were carried out for the case of single bubbles as well as bubbles rising in chains in grid generated turbulence. The data on rise characteristics of the bubbles along with liquid flow pattern are reported for the first time for the bubbles rising in surfactant solution in presence of controlled turbulence. An oscillating grid apparatus was used to generate nearly isotropic flow with nearly zero mean flow. The in-house image processing routines were used to deduce the trajectory of the bubbles along with the parameters describing bubble shape characteristics like the eccentricity and interface wobbling. The results indicated that the modification of rising velocity was a function of the turbulent characteristics, the bubble frequency and the surfactant concentration. The maximum interactions between the continuous and dispersed phases occurred at higher bubble frequency and higher surfactant concentration. The increase in turbulence intensity was observed to increase the bubble rise velocity at higher surfactant concentration.