Concentration in overflow

Interstage Mixing Efficiencies Mixing or stage efficiencies rarely achieve the ideal 100 percent, in which solute concentrations in overflow and underflow hquor from each thickener are identical. Part of the deficiency is due to insufficient blending of the two streams, and attaining equilibrium will be hampered further bv heavily flocculated sohds. In systems in which flocculants are used, interstage effi-... 

The sohd can be contacted with the solvent in a number of different ways but traditionally that part of the solvent retained by the sohd is referred to as the underflow or holdup, whereas the sohd-free solute-laden solvent separated from the sohd after extraction is called the overflow. The holdup of bound hquor plays a vital role in the estimation of separation performance. In practice both static and dynamic holdup are measured in a process study, other parameters of importance being the relationship of holdup to drainage time and percolation rate. The results of such studies permit conclusions to be drawn about the feasibihty of extraction by percolation, the holdup of different bed heights of material prepared for extraction, and the relationship between solute content of the hquor and holdup. If the percolation rate is very low (in the case of oilseeds a minimum percolation rate of 3 x 10 m/s is normally required), extraction by immersion may be more effective. Percolation rate measurements and the methods of utilizing the data have been reported (8,9) these indicate that the effect of solute concentration on holdup plays an important part in determining the solute concentration in the hquor leaving the extractor. 

When the overflow clarity is independent of overflow rate and depends only on detention time, as in the case for high soHds removal from a flocculating suspension, the required time is deterrnined by simple laboratory testing of residual soHd concentrations in the supernatant versus detention time under the conditions of mild shear. This deterrnination is sometimes called the second-order test procedure because the flocculation process foUows a second-order reaction rate. 

The reactor effluent is rapidly quenched with aqueous mother Hquor in specially designed equipment operating at pressures essentially equal to the reactor pressure. This operation yields an off-gas consisting of ammonia and carbon dioxide vapor and a crystalline melamine slurry saturated with ammonia and carbon dioxide. The slurry is concentrated in a cyclone mill. The mother Hquor overflow is returned to the quenching system. The concentrated slurry is redissolved in the mother Hquor of the crystallization system, and the dissolved ammonia is stripped simultaneously. 

After the tank is filled, pumping is continued and overflow is permitted at the same flow rate. Find the concentration in the tank when it first becomes fuU, and find how long it takes for the effluent concentration to get within 95% of the steady state value. 

These data may be evaluated by selecting different nominal overflow rates (equivalent to settling rates) for each of the detention-time values, and then plotting the suspended-solids concentrations for each nominal overflow rate (as a parameter) against the detention time. For a specified suspended-sohds concentration in the effluent, a cui ve of overflow rate versus detention time can be prepared from this plot and used for optimizing the design of the equipment. 

Many early studies of transmitter release depended on measuring its concentration in the effluent of a stimulated, perfused nerve/end-organ preparation. This technique is still widely used to study drug-induced changes in noradrenaline release from sympathetic neurons and the adrenal medulla. However, it is important to realise that the concentration of transmitter will represent only that proportion of transmitter which escapes into the perfusate ( overflow ) (Fig. 4.2). Monoamines, for instance, are rapidly sequestered by uptake into neuronal and non-neuronal tissue whereas other transmitters, such as acetylcholine, are metabolised extensively within the synapse. Because of these local clearance mechanisms, the amount of transmitter which overflows into the perfusate will depend not only on the frequency of nerve stimulation (i.e. release rate) but also on the dimensions of the synaptic cleft and the density of innervation. 

In fines removal, both the cut size and the grade efficiency are difficult to assess because of the limited accuracy of the sieve analysis technique and the problems Involved in the determination of the solids concentration in the overflow. For a. 65 m cyclone, whilst using a 20 mm vortexfinder diameter, an apex diameter of 16 mm and a feed flow of 1.6 1/s, solids recovery is over 99 % This recovery corresponds to a cut size between 50 - 100 pm. Typical distributions of size by weight, for the feed flow as well as the overflow are shown in Figure 5 Results are summarised in Table 2. 

The proof strength at which the volatility curve of a particular component intersects that of ethyl alcohol indicates that proof at which the minor constituent will be concentrated in a fractionating column at the limiting condition of total reflux. For practical conditions, the maximum concentration of a particular congener or minor component occurs at a proof in the column at which its volatility is approximately equal to the internal reflux ratio (L/V where L is the molal liquid or overflow rate and V the molal vapor rate). This can be established by the technique... 

Fig. 4 Effect of various peptides and nonpeptides on the electrically (3 Hz) evoked tritium overflow from superfused mouse brain cortex slices preincubated with 3H-serotonin. The evoked overflow represents quasi-physiological exocytotic serotonin release. In all experiments, serotonin autoreceptors were blocked by metitepine. The figure shows that human neuropeptide Y concentration-dependently inhibited serotonin release and that this effect was mimicked by human neuropeptide Y (13-36) (NPYi3 36), which has a high affinity for Y2 but a very low affinity for Yi receptors. These results are compatible with the view that neuropeptide Y acts via Y2 receptors in the present model. For the sake of comparison, the figure also shows the inhibitory effects of another three agonists, acting via cannabinoid CBi, histamine H3 and prostaglandin EP3 receptors and used at concentrations causing the maximum or near-maximum effect at their respective receptors. Drug concentrations in pM. P < 0.05, P < 0.003, compared to the control (from Nakazi et al. 2000 and Nakazi 2001 redrawn).

The dynamic model of the column consists of two ordinary differential equations per tray if equimolal overflow, constant tray holdup, and instantaneous liquid hydraulics are assumed. Molar flowrates and concentrations in mole fractions are used. The liquid holdup on each tray is 0.4 kmol ... 

A given separator has three main streams the feed, which carries the cells to be separated, the stream concentrated in cells (underflow), and the diluted stream (overflow), containing the cells that the separator was not able to capture. These three streams are shown in Figure 11.4. 

Pumping of liquid colors was inefficient until the development of the microprocessor. Some liquid color was simply measured into batches with dippers. If a pump was used to deliver liquid color to an extruder, synchronizing the pump with the process was nearly impossible. If the speed of the extruder varied, color concentration in the product varied. When the extruder stopped, the liquid color could overflow and make a horrible mess. 

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