Author(s): N. E. Lima Neto; David Z. Zhu; Nallamuthu Rajaratnam
Linked Author(s): N. Rajaratnam
Keywords: Eration; Bubbles; Entrainment; Nozzles; Turbulent flow
Abstract: This paper describes experiments on bubble plumes in a relatively large water tank to investigate the effect of nozzle type, including single/multiple orifice nozzles and a porous airstone, on the characteristics of the bubbles and the induced flow structure. Measurements of bubble characteristics and flow field surrounding the bubble core were obtained using a double-tip optical probe and particle image velocimetry, respectively. The results revealed that radial distributions of bubble diameter and velocity were well described by a straight line, while the specific interfacial area followed a Gaussian curve. The variation of cumulative liquid entrainment rate with height was well described by a straight line, while the variations of kinetic energy of the mean and turbulent flow near the bubble core were well described by a polynomial curve and an exponential curve, respectively. Bubble velocity did not change significantly with different nozzles, but bubble size decreased significantly while interfacial area, liquid entrainment rate, and kinetic energy of the mean and turbulent flow increased significantly by using the porous airstone instead of nozzles with large orifices. The results for a nozzle with multiple orifices of small diameter are comparable to those for the airstone, which suggests the suitability of its use for systems susceptible to clogging.
Year: 2007