On the coalescence of bubbles in highly turbulent flows*

The coalescence of bubbles immediately downstream of bubble-generating systems, such as regenerative pumps, has not been studied despite broad applications in gas-liquid systems for optimizing industrial processes in chemical reactors, petroleum transport, and wastewater treatment. The flow field here consists of a coalescence-dominated bubbly flow regime in an extremely high Reynolds number turbulent flow decaying rapidly downstream. Understanding the impact of the turbulent intensity/Weber number and air content on the rate of coalescence is important for developing reliable predictive models for process design in these applications. In this study, we explore the bubble dynamics in a duct connected downstream of a side-channel

pump. The high turbulent intensity in the pump (∼ 50%) significantly reduces the bubble sizes below the size distribution possible in a fully developed duct flow, creating a coalescence dominated regime along the duct immediately downstream of the pump. Experimental measurements of bubble size distribution are taken along the duct for different flow rates and air contents, and are also compared with Euler-Euler simulations coupled with a population balance approach, and direct numerical simulations of bubbles in isotropic turbulence to establish an in-depth understanding of the multiphase flow regime. The results will be discussed in detail during the talk.