Flow regime loading

FIGURE 1.36 General scheme for the process of CPC and mobile phase flow regime for the descending mode of CPC (insert bottom left) used for the CPC separation of dichlorprop with [mono-ll-octadecylthio-h ls-10,ll-dihydroquinidinyl)]-l,4-phthalazine as chiral selector. Elution profiles for dichlorprop after injection of 366 mg racemate, amolar ratio r = 1 of loaded dichlorprop to total selector present in the rotor, and arotor speed of 1100 rpm. Stationary phase, 10 mM selector in methyl tert-butylether mobile phase, 100 mM sodium phosphate buffer (pH 8) flow rate 3 mLmin temperature, 25°C. (Reproduced from E. Gavioh et ah. Anal. Chem., 76 5837 (2004). With permission.)... 

The time taken for a system to reach a desired pressure within the molecular flow regime cannot be calculated as simply as it can for viscous flow, because the outgassing of the various materials used in the construction of the system starts to play an important role in terms of the quantities of gas which have to be removed. However, since the product of the pressure in the system and the net pumping speed is equal to the total gas load (measured in units of pressure x volume) it is clear that the net pumping speed (Equation (1.4)) should be kept as large as possible. The molecular flow conductance of a long tube is given by... 

FIG. 14-19 The flow regime likely to exist on a distillation tray as a function of vapor and liquid loads. (From H. Z. Kister, Distillation Design, copyright 1992 hy McGraw-Hill reprinted hy permission.)... 

The flow regime likely to exist on a diet illation tray, as a function of vapor and liquid loads,... 

Pumping velocity 1 to 4 m/s 0.06 to 0.7 kW/Mg/h per km distance. Loading 0.3 to 1.7 kg solids/kg water. Economic trade-off between solids loading and pumping costs. Try to use the heterogeneous flow regime and consider adjusting pH to alter stability of dispersion. 

Spray regime operation is desirable (321) for negative-surface-tension systems (i.e., where the mixture s surface tension decreases from the top tray toward the bottom tray). Froth regime operation is desirable for positive-surface-tension systems (surface tension increases from the top tray down), and when liquid entrainment needs to be minimized (321). In most commercial applications, vapor and liquid loading requirements override these desirability considerations and dictate the tray flow regime. For optimum tray performance, the tray layout must therefore accommodate the expected flow regime. 

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