Flow regimes and transitions

Figure 17.7 Flow regimes and transition gas velocities in a bubble column slurry reactor (adapted from Shah et al., 1982).

Gourich B, Vial C, Essadki AH, AUam F, Soulami MB, Ziyad M. (2006) Identification of flow regimes and transition points in a bubble column through analysis of differential pressure signal— influence of the coalescence behavior of the hquid phase. Chem. Eng. Process., 45 214—223. 

The transition between the trickle-flow regime and the pulse-flow regime is plotted in the Figure 5.2—4 as a function of the superficial gas velocity, uc, the liquid velocity, uL, and the total reactor pressure, P, for the water-nitrogen system [17]. This figure shows clearly that the transition depends strongly on the pressure in the reactor. 

To verify the flow regime and the laminar-turbulent transition, a bronze block was replaced by an transparent altuglas plate. Visualisation with dye revealed a very stable flow for Reynolds numbers up to 2500 for both smooth and rough channels. On the contrary, large eddies were visualised for Reynolds numbers over 3800. Between these two values a stable flow region following turbulent structures were observed. 

As the flow enters the transition flow regime and eontinues into the free-molecular flow regime, the Knudsen number becomes significant enough that the molecular approach has to be utilized. Thus, the Boltzmann equation... 

The HEM will handle both laminar and turbulent flow regimes the HEV will not. This is a very significant advantage when scaling-up from small diameter mixers in the laboratory (perhaps 1/8") to large mixers in the plant. In the laboratory it may be that the flow regime is transition or laminar. 

Hydromorphological monitoring generally relies on series of elements such as assessment of quantity and dynamics of flow, connections to groundwater, continuity, channel patterns, width/depth variations, substrate conditions, structure and condition of the riparian zone in the case of rivers, residence time, lake depth variation, tidal flow regime, substrate condition and structure and condition of the intertidal zone, freshwater flow regime and direction and speed of dominant currents for transition/coastal waters. 

Unlike other equations in the table, this equation applies to all three flow regimes—laminar, transition, and turbulent. Its predictions for laminar flow are in agreement with /= 16/Re. The predictions for transition flow are subject to some uncertainty. However, the predictions for turbulent flow are comparable with those rendered by the preceding equation. 

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