Particle image velocimetry (PIV) measurements in bubble columns and gas cyclones.

摘要

Particle image velocimetry (PIV) is applied to study the flow fields and hydrodynamics in a bubble column with bubbles rising in a chain, and in a pilot gas cyclone separator. In the bubble column, it is observed that the bubble rising trajectory changes from one-dimensional to three-dimensional as liquid viscosity reduces. Bubbles rise with or without oscillatory and rotational motion depending on the trajectory of bubble rising. Different behaviors of gas bubbles introduce various instantaneous and time-averaged liquid flow structures. The bubble-induced pseudo-turbulence becomes more intense and its distribution less inhomogeneous in liquid of low viscosity.;In addition, a flow-adaptive data validation (FADV) scheme is proposed to remove spurious vectors in PIV data. The evaluation results show that the FADV scheme can effectively remove the spurious vectors, as well as avoid rejecting the valid vectors.;In gas cyclones, the turbulent swirling flows are three-dimensional. When they are investigated by two-dimensional particle image velocimetry (2D-PIV), contamination is introduced into the experimental results due to the existence of considerable out-of-plane velocity caused by the tangential gas motion. Contamination-removing methods are proposed in this work. The contamination on the axial velocity has been efficiently eliminated whereas that on the radial velocity is difficult to evaluate. In order to accurately investigate the tangential, axial, and radial velocity fields simultaneously, stereoscopic particle image velocimetry (Stereo-PIV) is applied for the first time in gas cyclones. The velocity fields are measured with gas inlet velocity of 7.2 ∼ 15.0 m/s. At the same time, flow properties such as vorticity, strain-rate, Reynolds stress, and turbulence intensity are investigated systematically.