Recycle-flow mixer

Figure 1.186 Schematic of the recycle-flow micro mixer with five mixing elements [56] (by courtesy of Transducer Research Foundation).

Mixer type Recycle-flow micro mixer Outlet channel width 50 pm... 

Figure 1.188 Microscope images of the color formation due to a reactive characterization of mixing in the five mixing elements of the recycle-flow micro mixer (Re = 28 150 pm). Phenolphthalein and NaOH solutions were mixed [56] (by courtesy ofTransducer Research Foundation).

The spreadsheet shows an initially assumed value of the recycle flow rate (ha) of 100.0 mol/s (Cell E13) and an assumed value of the mixing point outlet temperature of 50°C (Cell D8). The value of hi will be varied until the calculated recycle flow rate (/i4c) in Cell J13 equals the assumed value, which it now does not. (The actual calculation will be done by finding the value of 4a that drives the value of ha - ha in Cell 117 to zero.) Once the flow rates are correct, the mixing point temperature will be varied to determine the value that drives A// = S out out (in Cell D4) to zero for the adiabatic mixer. 

One of the promising designs is the modified Tesla structures [46]. It uses the Coanda effect to split part of the fluid stream and direct it so that it recombines with the opposing flow of the other part of the stream. Coanda effect micromixer relies on the redirection of a flow by a special guiding structure that creates new interfaces within the flow [47]. This special passive structure provides good mixing at low flow rates. In this way the Coanda mixer can also be seen as a special realization of the SAR approach using recycle flows [32]. 

Liquid industrial waste [10+]. One of the three streams that enter a mixer has a composition of 5 % w/w solids, 10 % w/w bacteria, and 7 % w/w heavy metals. The resulting stream from the mixer has a mass flow rate of 1,000 kg/h and a composition of 9.6 % w/w bacteria. Then this stream is fed to a settler, whose dense stream is 20 % of the input flow. The clarifled stream is fed to a sorter, which generates a recycle of 10 %, which is the second stream that enters the mixer. The flow of the clarifled stream that leaves the plant (leaves the sorter) has a composition of 1 % w/w solids. The dense flow has a composition of 20 % w/w solids and is then fed to a centrifuge that removes 30 % w/w moisture at a mass flow rate of 50 kg/h, which is the third stream that enters the mixer. The output stream of the centrifuge has 7 % of bacteria and is fed to an evaporator, which eliminates 60 % w/w humidity, generating a final stream with 40 % w/w solids. Calculate (a) the composition and mass flow rate of the clarified stream that leaves the plant (leaves the sorter), (b) the composition and mass flow rate of the stream that leaves the evaporator, (c) the composition and mass flow rate of the input and output streams of the settler, and (d) the Composition of the third stream that enters the mixer. 

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. 16. Two-hquid flotation flow sheet (39). The original ROM is kaolin (white clay) that contains 11% impurity in the form of mica, anatase, and siUca. Treatment produces high purity kaolin and a Ti02-rich fraction. A, Kaolin stockpile D, dispersant (sodium siUcate plus alkah) W, water K, kerosene C, collector (sodium oleate) RK, recycled kerosene S, screen M, inline mixer SPR, separator CFG, centrifuge P, product and T, to waste.

The final loose end in the process is the aqueous decanter product, A7. The hexane must be removed before the mixture can be sent to wastewater treatment, ie, accepted as a water by-product. Two opportunistic separations. Fractionators 12 and 13, are possible. Selection of Fractionator 13 gives pure water underflow, and a distillate similar to D5. Distillate D13 can be recycled back and mixed with D5 without affecting the operation of Mixer 1. AH streams are processed and the flow sheet produces both desired products (Fig. 5b). 

Jet Mixers Continuous recycle of the contents of a tank through an external pump so arranged that the pump discharge stream appropriately reenters the vessel can result in a flow pattern in the tank which will produce a slow mixing aciion [Fossett, Trans. Jnst. Chem. Eng., 29,322 (1951)]. 

The performance of the Sonogashira reaction is claimed to be the first example of a homogeneously metal-catalyzed reaction conducted in a micro reactor [120], Since the reaction involves multi-phase postprocessing which is needed for the separation of products and catalysts, continuous recycling technology is of interest for an efficient production process. Micro flow systems with micro mixers are one way to realize such processing. 

Both the contact efficiency of isobutane and olefin in the zones and the mixing efficiency of acid and hydrocarbon in these reactors are very important. The flow must be such that no isobutane recycle will bypass the reaction zone and no hydrocarbon will bypass the acid-hydrocarbon mixing zone. With this type of unit, a mixer driven by a 40-hp. motor is usually used in each of the zones. A reactor containing five such mixers can normally make 1500 bbl. per day of alkylate. The seven-zone reactors can make 3400 bbl. per day of alkylate. 

The three component streams are in a recycle mode at the desired flow rates before foaming. During foaming, surfactant and precursor are premixed before they come in contact with the polyisocyanate in the power mixer. The foaming mixture is then discharged through multiple nozzles in the spreader (Figure 5). 

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