Suspension stream

Consider the impingement between two opposed particles-gas suspension streams from accelerating tubes of the same diameter. The assumptions made in the establishment of the model are (1) The streams are symmetrical with respect to both the jet axis and the impingement plane (2) The gas flow velocity and all the physical properties of gas and solid are kept constant and (3) The particles beyond collision penetrate into the opposing stream up to. rlllas, while any particle will be drawn out of the system immediately once it collides with another particle. 

In order to obtain experimental evidence for understanding the influence of the impingement between the opposing droplets-in-gas suspension streams on the dispersity of liquid, and also to get some practically applicable information for designing and operating impinging stream devices, the experimental investigation described below was carried out. 

The larger the value for cr, the greater the scattering of the size distribution, and, correspondingly, the poorer the uniformity of the droplet sizes. Part of the data measured at various air-to-liquid mass flow ratio, m.JmL, are shown in Table 5.1. It can be seen that, normally, the impingement between opposing droplets-in-gas suspension streams makes cr smaller. Only those obtained at in the third column of the... 

The impingement between the two opposing suspension streams makes the sizes of the spray droplets uniform to an extent, yielding narrower size distribution. More intensive impingement favors the uniformization of droplet sizes more effectively. 

Essentially, the impingement between the two opposing droplets-in-gas suspension streams does not change the mean diameter of the droplets. 

It should be noted that the impingement or impacting of a solid-gas suspension stream on a solid surface can also result in the effect of grinding and milling. However, as mentioned in Section 8.1, flow configuration is beyond the scope of this book. 

Fig. 9.5 Hydrodynamic focusing. Suspension is focused on the axis of the measurement opening M with a probe D. The suspension streams through the axis after dilution with particle free electrolyte E.

In filtration unit operation, especially in microfiltration, one usually differentiates between dead-end filtration (with cake formation) and cross-flow filtration [25] (Fig. 5). The cross-flow filter can have different geometries (Fig. 6) phase membranes, tubular membranes, or pleated membranes, of which the tubular and pleated ones are already accepted as cross-flow geometries in reactor technology, as mentioned above. In filtration engineering the cross-flow term means that the filtrate flows perpendicularly to the suspension stream. Cross-flow may not be considered a sufficiently illustrative term here [25]. A better term would be parallel filtration, but the term cross-flow filtration has been accepted generally and may be difficult to change at present. 

Countercurrent, in which gas (or solid suspension) streams flow in opposite directions... 

In horizontal elutriators a stream of suspension is passed over a reservoir of clear fluid. The larger fineparticles leave the suspension stream and are collected at the bottom of the settling chamber. The fractionation efficiency of this device is not good since some fineparticles of all sizes will leave the suspension stream as it moves over the clear fluid in the collection chamber. The solids concentration of the feed stream must be kept low, otherwise, bulk penetration by the feed layer into the fluid in the container will occur (see discussion of the stability of the line start suspension system in Chapter 4). It is possible to use a more dense fluid in the reservoir to improve the stability of the system but this system has not been used in size characterization studies. Fineparticles that drop through the full height of the fluid stream in the time taken for the fluid stream to move across the elutriating chamber are completely removed from the feed stream. 

An instrument developed for the characterization of submicron fineparticles is shown in Figure 6.13. Fineparticles too small to be resolved as images can still be seen in dark-field-illuminated microscope systems by the scintillations of light that they create as they move into the plane of the microscope. Techniques for studying objects in this way are described as ultramicroscopy. The instrument shown in Figure 6.13 exploits ultramicroscopy and the measurement procedure is known as flow ultramicroscopy . In the original system developed by Davidson, Collins and Haller, a suspension stream of latex was made to flow up and through the plane of a dark-field-illuminated microscope and the scintillations created by the presence of the latex fineparticles counted... 

Dewatering is a filtration process where a suspension stream of consistency d is divided by a filter into a thickened part with a consistency of Ct and a filtrate stream of consistency Cf. At the start of filtering the retention of the solids on the filter is lowest. With time mat thickness increases, as does retention, which means that the solids content in the filtrate decreases. Dewatering usually aims for zero consistency in the filtrate, which in practice is not reached as retention is never 100%. In contrast, washing takes advantage of this effect for solid/solid separation. 

In practical applications this can lead to situations where a suspension stream of 3000 1/h has to be mixed effectively with a chemicals stream of as little as 0.5 1/h, i.e. one thousands of the volume flow or less. 

One reason for the generation of the varied internal structures can be found in the droplet generation during spraying For the two fluid nozzle, the suspension mass flow is ripped by the parallel inserted nozzle gas. For the rotational atomizer, the droplet generation is an effect of the ripping of the suspension stream because of... 

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