Static mixers measurement

This study has shown the possibility to measure segregation problems when discharging mixtures through a funnel. It has also shown the effect of the number of drum revolutions at a fixed speed on the quality of a mixture, as well as the effect of a static mixer. The axial structure of the mixtures through autocorrelation functions could also be studied from these data, but this has not been reported here for clarity of the paper. In addition, it must be remembered that we just studied the evolution of the dielectric permittivity, and that in most cases, we will have to follow the volumetric compositions of each component in order to characterise the homogeneity of the medium. The capacitive method is indeed full of promise for particulate systems, and it would be interesting to explore it much into details, particularly for determining the proportions of each component of the mixture. 

Figure 10.47 shows for the % in. inside diameter mixer reactor the importance of the initial molar feed ratio. For relatively low initial molar feed ratios (below about 1.0) the recycle loop/static mixer system can actually give poorer performance than the agitated vessel without a recycle loop. The data indicate that this ratio should be kept above 3 to ensure that the recycle loop/static mixer system is used to fullest advantage. At recycle ratios of 2.4, the feedpipe velocity had a minor, although measurable, effect on the yield of the slowest reaction. 

Measured Laminar Mixing Efficiency for Selected Static Mixers... 

Measured values of e for several static mixers are ranked in Table 9.24. The corresponding a, for comparison, is shown in Figure 9.46. 

These interesting devices consist of a tube or duct within which static elements are installed to promote cross-channel flow. See Figure 8.5 and Section 8.7.2. Static mixers are quite effective in promoting radial mixing in laminar flow, but their geometry is too complex to allow solution of the convective diffusion equation on a routine basis. A review article by Thakur et al. (2003) provides some empirical correlations. The lack of published data prevents a priori designs that utilize static mixers, but the axial dispersion model is a reasonable way to correlate pilot plant data. Chapter 15 shows how Pe can be measured using inert tracers. 

The two dimensionless groups are based on the empty pipe diameter (D,), including the value of u, which is a superficial velocity. In principle it only requires one value of AP to be measured at one value of v, to define the product Re for any static mixer but a range of measurements can give useful information regarding the slight variability of tf> Re and also the upper limit of the laminar flow regime in terms of Re ... 

The turbulent flow characteristics of the static mixer are less well documented than those for laminar flow, probably because of the more recent emphasis on turbulent applications and the background of development for laminar flow applications. Turbulent mixing has been modelled in terms of eddy size for the Sulzer mixer. Measurements of mass transfer have been made and data are available for drop size in liquid-liquid dispersions for Kenics - ", Sulzer and Lightnin mixers. 

This book is unique in its consistency in terminology and units. Tower or column motionless mixer or static mixer tray or plate - these are just some of the terms that are used interchangeably when discussing process equipment. In this book consistent use of terms has been applied. The SI units of measurement are used throughout the text. 

D. Dechlorinated Brine Discharge System. This is the most difficult control loop in the brine system. Neutralization takes place in a static mixer. Caustic enters through an injector nozzle upstream of the mixer, and pH is measured close downstream. The starting pH of the brine is normally less than 2.0, and the end-point is between 8.0... 

In experimental studies, however, the striation concept is not often used. This has to do with the difficulty in accurately determining the number of striations beyond the level of coarse mixing. Another measure of mixing is the coefficient of variation (COV), discussed earlier. The COV has been used in several experimental studies to compare the goodness of mixing in various static mixers. 

In labyrinth or honeycomb flocculators (static mixers) the head loss has to be measured experimentally with a prototype module in a test rig. Then equation 4.57 can be used to calculate the power dissipation and, hence, the mean velocity gradient G. 

Flow patterns in the Kenics static mixer are too complicated to determine the residence time distribntion analytically. Instead, experimental measurements were fit to a simple model. The model nsed for the Kenics mixer in Table 1-3 assumes regions of undisturbed laminar flow separated by planes of complete radial mixing, there being one mixing plane for every four Kenics elements. Simpler models are useful for systems in turbulent flow. 

It is wise to use a size of static mixer for which manufacturer s friction factor data are available and to ensure confidence in any data of this type before using them in any further correlation. Whenever possible, the friction factor should be measured during the experiment. 

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