Measurements of the size, rise velocity, and specific interfacial area of bubbles in an impinging-jet bubble column

Abstract

A 2-D laser particle dynamics analyzer was used to simultaneously measure the bubble size, bubble rise velocity, bubble size distribution, and gas-phase turbulence intensities in an impinging-jet bubble column that utilized two venturi injectors to create turbulent gas–liquid jets in the ambient fluid. These measurements were conducted in clean deionized water and in a Kraft pulp mill effluent that was ozonated using a wide range of utilized ozone doses. The intersecting of the gas–liquid jets caused an increase in the turbulence produced in the ambient fluid and as a result, the count mean bubble diameter (dB) and the Sauter mean bubble diameter (dS) were smaller than those obtained in conventional bubble columns. This has led to a significant increase in the specific gas bubble interfacial area (a) compared to that in conventional bubble columns. The count mean bubble and Sauter mean bubble diameters were found to be dependent on the superficial gas and liquid velocities (uG and uL, respectively). The count and Sauter mean bubble diameters were smaller in the raw Kraft pulp mill effluent compared to those in the deionized water. This has led to a significant increase in the specific gas bubble interfacial area and gas hold-up (εεG) compared to those in the deionized water. As the raw Kraft pulp mill effluent was ozonated and the amount of utilized ozone increased, the count mean and Sauter mean bubble diameters increased. The bubble size distributions exhibited different trends depending on the type of the test liquid and on the operating conditions in terms of uG and uL. Generally, those distributions could be well described using normal, gamma, or log-normal density functions. Key words: laser, phase, Doppler, impinging-jet, bubble column, bubble, size, gas hold-up, interfacial area.