Mixing rate

The decay constant is the key to the mixing rate number defined for Re > lO" by N/ D/TY = 0.5 for a disk flat blade turbine (DFBT), and N/ (D/TY = 0.9 for the propeUer. Therefore, power required to achieve any degree of uniformity in a fixed time is proportional to D and D for DFBT and propeUer, respectively. 

Fig. 31. Comparison of mixing rates with different static mixers A, Lightnin B, Komax C, Etoflo HV D, Kenics E, SMXL E, Hi-Mixer and G, SMX.

Flame Types and Their Characteristics. There are two main types of flames diffusion and premixed. In diffusion flames, the fuel and oxidant are separately introduced and the rate of the overall process is determined by the mixing rate. Examples of diffusion flames include the flames associated with candles, matches, gaseous fuel jets, oil sprays, and large fires, whether accidental or otherwise. In premixed flames, fuel and oxidant are mixed thoroughly prior to combustion. A fundamental understanding of both flame types and their stmcture involves the determination of the dimensions of the various zones in the flame and the temperature, velocity, and species concentrations throughout the system. 

Polymers which already have a long chain structure may provide a good floe at low mixing rates. Often the turbulence and detention in the clarifier inlet distribution is adequate. 

Mixing rate constants for fully turbulent flow regimes (Npg > 10,000)... 

Whenever reaction rates are of the same magnitude as, or faster than, the mixing rate in a stirred reactor, mixing will have a... 

Many reactions involve shear-sensitive materials, which severely limit the maximum mixing rate and make impeller and reactor design important. Mixing becomes the limiting factor. 

The data plotted in the figure clearly support the predicted positive dependence of crystal size on agitation rate. Precipitation in the crystal film both enhances mass transfer and depletes bulk solute concentration. Thus, in the clear film model plotted by broken lines, bulk crystal sizes are initially slightly smaller than those predicted by the crystal film model but quickly become much larger due to increased yield. Taken together, these data imply that while the initial mean crystal growth rate and mixing rate dependence of size are... 

Jones, A.G., Hostomsky, J. and Zhou Li, 1992a. On the effect of liquid mixing rate on primary crystal size during the gas-liquid precipitation of calcium carbonate. Chemical Engineering Science, 47, 3817-3824. 

Determine the cementing operation time and thus the minimum thickening time. Assume a cement mixing rate of 25 sacks/min. Also assume an annular displacement rate no greater than 90 ft/min while the spacer is moving through the open-hole section and a flowrate of 300 gal/min thereafter. A safety factor of 1.0 hr is to be used. 

Considerable confusion thus seems to exist in the literature regarding the influence of rheological properties on mixing rates and times. Exhaustive reviews are available on this subject l636i. 

When this relation is satisfied, the conversion will be limited by the reaction kinetics, not by the mixing rate. As a practical matter, the assumption of perfect mixing is probably reasonable when is eight times larger than... 

Moore WS (2000) Determining coastal mixing rates using radium isotopes. Cont Shelf Res 20 1995-2007 Moore WS, Shaw X J (1998) Chemical signals from submarine fluid advection onto the continental shelf J GeophysRes 103 21543-21552... 

Values of Db determined by " Th profiles commonly range from 1 to 50 cm7y in estuarine and slope sediments (Aller and Cochran 1976 Aller et al. 1980 Sun et al. 1994 Gerino et al. 1998 Green et al. 2002) to < 10 cm7y in the deep sea (Aller and DeMaster 1984 Pope et al. 1996). Although there is some overlap, mixing rates in the deep sea tend to be lower than those in nearshore sediments. This trend has been documented with °Pb profiles as well (e.g., Henderson et al. 1999). 

Figure 12. An example of use of to assess the rate and depth of sediment mixing from a core on the slopes of the Bahamas (Henderson et al. 1999b). The exponential decrease in Pbxs seen in the upper 6 cm of the sediment reflects decay of °Pb as it is mixed downward. The diffusional model of mixing described in the text indicates a mixing rate, D, of 51 cm kyr for this core. The two circled points at greater depth reflect rapid injection of surface material to depth in a process known as conveyor-belt feeding (Robbins 1988 Smith et al. 1997).

Where Ao is the activity at the sediment surface, w is the sedimentation rate (cm yr ), D is the mixing rate (cm yr ), is the decay constant for the nuclide of interest (yr ) and z is the depth in the sediment (cm). In some near-shore environments both sedimentation and bioturbation must be considered. But in most open marine environments the sedimentation rate is sufficiently slow that it can be ignored and the equation simplifies to ... 

D, the mixing rate, varies widely depending on environment. Boudreau (1994) comprehensively summarized measurements of D from some 36 papers including 22 using °Pb and 7 using These studies indicated mixing rates varying from 0.02... 

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