Bubble formation at top-submerged nozzles immersed in a quiescent liquid

Abstract

Mixing is one of the most common unit operations used in radiochemical plants. In such plants, air induced mixing is preferred which is an economic and efficient means for mixing of the radioactive solutions without using moving parts. Intensity of air induced mixing depends on the diameter of the bubbles produced by the device used for air induced mixing. A typical device used for air induced mixing consists of multiple holes. To predict the diameter of the bubbles formed by a mixing device, a thorough understanding of the phenomenon of bubble formation at adjacent multiple holes is needed. The present study, which focuses on bubble formation at the hole at the tip of a top-submerged nozzle, is a step in this direction. In this study, the experiments are carried out to study bubble formation at top-submerged nozzles of different diameters. Demineralized water, nitric acid of different molarities and organic phase containing 30% (v/v) tributyl phosphate dissolved in dodecane equilibrated with nitric acid of different molarities are used in the experiments. These liquids are selected due to their relevance in nuclear chemical processes. Effects of air flow rate, nozzle diameter and the liquid used on bubble diameter and bubble detachment time are quantified using high speed imaging. Previously reported correlations to estimate the diameter of bubbles formed at top-submerged nozzles are compared with the data generated in the present study and found to be inadequate. Hence, a new correlation using relevant dimensionless numbers (Bond number, Froude number and Galileo number) is regressed utilizing the experimental data.