Author(s): Iran E. Lima Neto; David Z. Zhu; Nallamuthu Rajaratnam
Linked Author(s): Iran E. Lima Neto, David Z. Zhu
Keywords: Eration; Bubbles; Jets; Mixing; Turbulence
Abstract: Air-water bubbly jets have a wide range of environmental engineering applications. Compared to the injection of pure air, the injection of air-water mixtures has additional advantages, such as production of small bubbles without the need of porous diffusers, which are susceptible to clogging, and higher energy efficiency for mixing purposes. Moreover, air injection into an effluent diffuser can also avoid the use of additional air diffusers for mixing and aeration in lakes and rivers. In the present study, vertical upward air-water bubbly jets with a gas volume fraction, ε, of up to about 70% and nozzle Reynolds number, Re, ranging from about 10,600-17,700 are investigated experimentally in a relatively large water tank. Measurements of the liquid flow surrounding the bubbly jets are obtained with Particle Image Velocimetry. The power spectra of the velocity components are studied and a cut-off frequency is used to estimate the turbulent kinetic energy and Reynolds stresses. The results revealed nearly isotropic turbulent flow conditions for all experiments, and both the turbulent kinetic energy and Reynolds stresses increasing with axial distance from the nozzle. These parameters also appear to increase with the gas volume fraction, ε, and the nozzle Reynolds number, Re. Finally, a correlation is obtained to relate the depth-averaged turbulent kinetic energy near the bubbly jets with a function of ε`4/3 and Re`1/2. The results obtained in this study will be useful for estimating the potential of turbulent mixing induced by bubbly jets for applications in water and wastewater treatment and restoration of water bodies.
Year: 2009