Mixer in-line

As remarked earlier, because in-line static mixers are plug flow devices, the gas fraction is comparatively easy to determine from the ratio of mean gas flow rate to total flow rate, with adjustment for bubble slip if the flow orientation is nonhorizontal. Often, vertical downflow is preferred, since the gas-buoyancy leads to the bubble velocity being less than the liquid velocity, so the gas fraction (and hence the gas-liquid interface area) is greater than for other configurations. While there is much literature on bubble slip velocities, the predictions are said to be unreliable (Zuber and Findlay, 1965) and it is usually preferred to use empirical correlations of the gas fraction based on measurements [such as those in Middleton (1978)], although so far these all seem to be for air-water systems with negligible depletion of bubble size, so may need adjustment for other systems. 

Gas fraction in agitated vessel is difficult to predict a priori, but in the homogeneous regime, scale-up can be made reasonably accurately using empirical correlations. These are best expressed in the form 

These equations are for operation at ambient temperatme. In the fully turbulent regime there is a dependence of void fraction on temperatme which is discussed below. This gives ([) a Measmements of the void fraction distribution in gas-sparged vessels clearly show a region of high gas fraction in the violently 

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The natural process of bringing particles and polyelectrolytes together by Brownian motion, ie, perikinetic flocculation, often is assisted by orthokinetic flocculation which increases particle coUisions through the motion of the fluid and velocity gradients in the flow. This is the idea behind the use of in-line mixers or paddle-type flocculators in front of some separation equipment like gravity clarifiers. The rate of flocculation in clarifiers is also increased by recycling the floes to increase the rate of particle—particle coUisions through the increase in soUds concentration. 

FIG. 23-25 Typ es of industrial gas/Hqiiid reactors, (a) Tray tower, (h) Packed, counter current, (c) Packed, parallel current, (d) Falling liquid film, (e) Spray tower, if) Bubble tower, (g) Venturi mixer, h) Static in line mixer, ( ) Tubular flow, (j) Stirred tank, (A,) Centrifugal pump, (/) Two-phase flow in horizontal tubes. 

Wiped film stills in place of continuous still pots —Centrifugal extractors in place of extraction columns —Flash dryers in place of tray dryers —Continuous reactors in place of batch —Plug flow reactors in place of CFSTRs —Continuous in-line mixers in place of mixing vessels... 

Finally, mixing can be induced by physically splicing the fluid into smaller units and re-distributing them. In-line mixers rely primarily on this mechanism, which is shown in Figure 7.4. 

Continuous in-line mixers in place of mixing vessels... 

Soluble liquids Mixing Agitated vessel, in-line mixer... 

In-line mixers manufactured by, for example, Kenics, Lightning, and Sulzer are also applicable for continuous small-scale testing of a solvent extraction process, and 1 inch diameter models are available. This mixer system can be used either horizontally or vertically. However, few data are available for this type of contactor, although they would appear to offer many possibilities, not only for liquid-liquid systems, but also for use in... 

Figure 10.14. Some kinds of in-line mixers and blenders, (a) Mixing and blending with a recirculating pump, (b) Injector mixer with a helical baffle, (c) Several perforated plates (orifices) supported on a rod. (d) Several perforated plates flanged in. (e) Hellical mixing elements with alternating directions (Kenics Corp.). (f) Showing progressive striations of the flow channels with Kenics mixing elements.

Experts predict a trend from stirred-vessel mixing to the use of continuous mixing, e.g. by in-line mixers [1]. This again provides a chance for many microstructured mixers. 

Maintenance of a stable emulsion in the continuous metering system s total product flow is critical for an efficient margarine production and is achieved through the use of specially designed static in-line mixers. These are installed in the main pipelines downstream of the metering system as can be seen from Figure 27. 

The choice of the optimum style of in-line mixer is not nearly as certain as is the choice of the optimum style of agitator impeller. However, a firm recommendation can be made based on the experimental record and on judgment. There are several considerations that lead to the recommendation of the Kenics helical element mixer (HEM) as the most suitable mixer for handling fast consecutive reactions ... 

Scale- Up Agitated Vessels with Recycle Loops with Semi-Batch Feed to an In-Line Mixer in the Recycle Loop. Knight (1995) and Colleagues (1995) conducted a rather definitive study that determined the pertinent scale-up parameters for a static mixer in a recycle loop. They used a 20 liter semi-batch reactor agitated with... 

Recommendations for Handling Blending Requirements for Fast Reactions. For handling fast reactions, if the power requirements are unreasonable to maintain equal blend time on scale-up, then one should consider two alternates (1) inject the semi-batch feed into a recycle loop in the inlet of a static mixer and (2) do the reaction in-line while pumping out the vessel through an in-line mixer. 

Fig. 8 Ultra-hygienic in-line mixer. (Courtesy of Silverson Machines, Inc., East Long Meadow, Massachusetts.)...

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