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The spatial distribution of gas holdup in a stirred tank with a Rushton impeller and i.d. of 380 mm was measured by the fiber optic technique to show the different gas−liquid flow patterns including flooding. The data on loading/flooding transition are found consistent with the general correlation. The experiments were also simulated numerically by the Eulerian−Eulerian approach with the control volume formulation with the k−ε−A p two-phase turbulence model, and different flow patterns in the gas−liquid stirred tank were well demonstrated. It is found that the gas holdup in the impeller discharge stream is underpredicted, but in the broad bulk flow region the results of simulation are in good agreement with the experimental data.

A new vision probe based on telecentric photography has been developed for multiphase system measurement. Four outstanding advantages of the probe are as follows: (i) Sharp pictures with little image distortion can be obtained because of the distinctive parallel light paths from the telecentric lens. (ii) The slim probe can be inserted everywhere in large reactors. (iii) Local characteristics such as particle (solid particle or drop or bubble) size, holdup, and interfacial area with one or even more dispersed phases can be measured. (iv) The higher holdup of the dispersed phase is allowed. The robustness of the probe has been tested in a multiphase reactor. Finally, applications in solid−liquid, gas−liquid, and gas−liquid−solid stirred tanks are present respectively to demonstrate the measurements on the particle holdup, bubble size, and particle and bubble size using this vision probe.

The experimental data on the holdup of the dispersed phase in a Rushton impeller agitated stirred tank are presented. Experimental measurement is performed utilizing the sample withdrawal method to obtain the local dispersed-phase holdup in a laboratory-scale stirred tank under a variety of operating conditions. Three-dimensional turbulent two-phase liquid-liquid flow in the stirred tank is also numerically simulated by solving the Reynolds-averaged Navier-Stokes equations of two phases formulated by the two-fluid model. The turbulence effect is formulated using a simple two-phase extension of the well-known k-turbulence model by adding an extra source term generated from the presence of the dispersed phase in the turbulent kinetic energy transport equation of the continuous phase. A modified "inner-outer" iterative procedure is employed to model the interaction of the rotating impeller with the wall baffles. The modelpredicted mean velocity, turbulence characteristics of the continuous phase, and holdup profiles of the dispersed phase are compared against the published experimental data and the present measurements to validate the computational procedure, and good agreement is found up to a rather high overall dispersed-phase holdup case (30 vol %).

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