Mixer concentration gradients

In relatively small-scale operations, where frequent shutdowns may be desirable, as at night or during week ends, the mixer-settler plant offers the advantage that concentration gradients are maintained within the plant indefinitely even though operations have stopped. On start up, steady-state conditions are established immediately, product specifications are met with the first effluents, and recycling of the first products withdrawn is unnecessary. The agitated vessel is also eminently suitable for purely batch processes, which are likely to be on a small scale. 

Figure 1.133 Fluorescence micrographs obtained in a mixer using flow rotation and break-up. (a) Cross-sectional images showing the break-up which produces the smaller fragments of blobs. Thereby, the interfacial area is increased and large concentration gradients are provided, (b) Top of the mixer, clearly showing the propagation of one fluid into the other [146] (by courtesy oflOP Publishing Ltd.).

Mixer 90 [M 90] Serial-diffusion Micro Mixer for Concentration Gradients... 

Mixer type Serial-diffusion mixer for concentration gradients Channel depth at dam structure 5 pm... 

Vd is the so-called gradient dwell volume [i.e., the volume of the mobile phase contained in the instrument parts (mixer, filter, and tubing) between the pump and the column]. In an ideal case, linear concentration gradients in RPLC correspond to linear solvent strength (LSS) gradients according to the model developed by Snyder and Dolan " hence, Eq. 4 describes the retention data in LSS gradient elution. 

Concentration Gradient Generation and Control, Fig. 3 (a) Two-input mixer module, (b) Schematic of the microfluidic chamber, (c) Normalized fluorescence... 

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. 

To improve the mixing quality in the tubular reactor, Kenics type in-line static mixer reactor was employed. The in-line static mixers were designed to mix two or more fluids efficiently since an improved treinsport process such as flow division, radial eddying, flow constriction, and shear reversal eliminated the gradients in concentration, velocity and temperature. However, only 70 % conversion was achieved with one Kenics mixer unit. As shown in Table 2, five mixer units were required to achieve the maximum conversion. 

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