Gas Mixing Around the Jetting Region

26 for a nominal jet velocity of 32.6 m/s and with two different aeration flows outside the jet. The concentration profiles penetrate farther into the emulsion phase when there is less aeration flow outside the jet. The concentration profiles obtained at different elevations are also approximately similar if the local tracer concentration is normalized with the maximum tracer concentration at the axis, C/Cm, and plotted against a normalized radial distance, d(r1/2 c, where (r1/3)c is the radial position where the tracer concentration is just half the maximum tracer concentration at the axis (see Figs. 27 and 28). Thus, we experimentally determined that, in a permanent flamelike jet in a fluidized bed, not only the velocity profiles in the jet, but also the gas concentration profiles, are similar. 

The resulting velocity profiles and the flow pattern inside and around the jet are shown in Figs. 29 and 30 for a jet velocity of 32.6 m/s and with two different aeration flows. The jet boundary at Vz = 8 m/s shown in Figs. 29 and 30 was calculated from Tollmien similarity. The boundary where the tracer gas concentration becomes zero, C = 0, was determined from the normalized experimental tracer gas concentration profiles shown in Figs. 

27 and 28. The arrows in Figs. 29 and 30 indicate the actual axial and radial flow components, and the magnitudes are in m/s. The gas flow direction is predominantly from the emulsion phase into the jet at distances close to the jet nozzle. This flow can be from the aeration flow in the emulsion phase, as in the cases of high jet velocity or high aeration flow, or from the flow recirculated from the upper part of the jet. The 

The axial velocity profiles, calculated on the basis of Tollmien similarity and experimental measurement in Yang and Kcaims (1980) were integrated across the jet cross-section at different elevations to obtain the total jet flow across the respective jet cross-sections. The total jet flows at different jet cross-sections are compared with the original jet nozzle flow, as shown in Fig. 31. Up to about 50% of the original jet flow can be entrained from the emulsion phase at the lower part of the jet close to the jet nozzle. This distance can extend up to about 4 times the nozzle diameter. The gas is then expelled from the jet along the jet height. 

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