In order to reveal the effect of baffles on flow structure and cyclic variation stirred by Rushton turbines, particle image velocimetry experiments were performed in baffled and unbaffled stirred tanks. In a baffled tank, the peak value of time-averaged velocity obviously increases, the high velocity region enlarges significantly, and the fluctuation of fluid elements near the turbine increases significantly. In the 20° phase plane of the baffled tank, the high swirl strength region slightly enlarges, but the peak of phase-resolved swirl strength is lower. The peak value and high value regions of turbulent kinetic energy are larger in the baffled stirred tank at various phase planes. Using quadruple proper orthogonal decomposition, the flow field is decomposed into a small-scale part, a transition part, a large-scale part, and a mean part with different spatial scales. Adding the baffle, the mean part with largest spatial scale obviously increases (it is favorable for mass transfer at different liquid levels) and the transition part, which mainly includes the random fluctuation of a turbulent cascade, slightly enhances (it is conducive to diffusion). The main influence of cyclic variation for various blade passages is the flow with large-scale, and the standard deviation of time coefficients decreases by 3%–4% for the mean part and the large-scale part by adding the baffle.
Adding a small amount of surfactant to a gas-liquid two-phase flow can markedly change the dynamic behavior of its bubbles. In this study, the lateral motion of a single bubble ( deq=1.99-3.33 mm, Reb=200-420) contaminated by surfactant and rising in a linear shear flow is experimentally studied. Sodium dodecyl sulfate (SDS) is chosen as the surfactant with concentrations ranging from 10 ppm to 50 ppm. A curved screen is used to generate a stable linear shear flow, and particle image velocimetry (PIV) is used to measure the quality of the flow field. Bubble motion parameters, including trajectory, aspect ratio, instantaneous velocity, terminal velocity, are captured using the shadow method with charge-coupled device (CCD) cameras. The lift coefficient CL is obtained by quasi-steady-state analysis. The results show that the presence of surfactant inhibits the lateral migration of bubbles rising in a shear flow and that increasing the SDS concentration and bubble equivalent diameter strengthens this inhibition effect. That is, the CL and the net lateral migration distance decreased with SDS concentration and bubble equivalent diameter. In addition, the variation trends of the quasi-steady drag coefficient, bubble terminal velocity, and bubble oscillation frequency with bubble equivalent diameter and SDS concentration also were analyzed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.