Separation by Rotating Flow

Separation based on rotating flow principles is one of the most common operations involved in gas-solid flows. This section describes the fundamental rotating flow principles and their applications to cyclone operation. The efficiency of dust collection in cyclones is also described. 

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The flow geometry assumed is illustrated in Fig. 14.21. The gas mixture is assumed to be rotating at uniform angular velocity co in a semicircular groove of radius a. Centrifugal equilibrium is established where the mixture is separated by the flow divider at radius c into an iimer, light fraction enriched in hydrogen and Fs and an outer, heavy fraction depleted in these components relative to UF. ... 

As a result, there is a growing trend to off-line clean reverse-pulse filters by using bags with multiple compartments. These sections allow the outlet-gas plenum serving a particular section to be closed off from the clean-gas exhaust, thereby stopping the flow of inlet gas. On the dirty-side of the tube sheet, the isolated section is separated by partitions from the neighboring sections where filtration continues. Sections of the filter are cleaned in rotation as with shaker and reverse-flow filters. 

Under this heading are grouped a number of investigations in which a finite volume of electrolyte is stirred either by rotation of the electrode, or where this stirring (or circulation) is accomplished independently (see Table VII, Part F). In principle, the boundary separating these types of flows from laminar flows discussed earlier is not sharp. 

The independence from a power supply makes PASs popular options for measurements of POCs in the remote alpine atmosphere, but they also limit the temporal resolution that can be achieved. Trying to combine the advantages of both PAS and active samplers, a flow-through sampler (FTS) was recently designed, which requires no external power source, but can sample large volumes of air in fairly short periods of time [18, 19] by rotating into the wind and have it blow through a series of PUF disks. The volume of air sampled can be estimated from wind speed records. The FTS will trap particles, but they cannot be analyzed separately from the gas phase POCs. 

A so-called Couette pump is illustrated in Fig. 4.20. Assume that the central shaft has a radius of rs = 0.08 m and the outer housing has a raduis of r/, =0.1 m. The feed flow and the out flow are separated by a 90° section where the clearance between the shaft and the outer housing is only 1 mm. Under normal operating conditions the shaft rotates at 800 rpm. 

Fig. 6.13 Comparison of streamlines from rotating-disk solutions at two rotation rates. Both cases are for air flow at atmospheric pressure and T = 300 K. The induced inlet velocity is greater for the higher rotation rate. In both cases the streamlines axe separated by 27tA4< = 1.0 x 10-6 kg/s. The solutions are illustrated for a 2 cm interval above the stagnation plane and a 3 cm radius rotation plane. The similarity solutions themselves apply for the semi-infinite half plane above the surface.

For case (a), the flow field consists of a single convective cell which circulates around an elliptic point (center) located at X= Y= 0 [28], For case (b) the flow field consists of two counter-rotating cells with centers at X = 0 and Y = 0.58. The cells are separated by the surface Y= 0. For case (c), the flow field is similar to (b) in the sense that the flow field consists of two counter-rotating cells separated by the surface at X= 0. The centers of rotation are at X= 1 and Y = 0. For case (d), the flow field consists of four counter-rotating cells separated by two surfaces at X = 0 and Y = 0. 

The two contributions to the rate of rotation, li, of the rod are convection and Brownian diffusion. Unlike the elastic dumbbell, where the springs were allowed to deform by the flow, the fixed separation of the beads in the rigid dumbbell must be maintained. For that reason, the vector u can rotate, but it cannot stretch. This constraint is satisfied by ensur-... 

Example 6.1 The Synthesis of the Roll Pump Consider building block 1 in conjunction with an infinite surface created by a rotating solid cylinder, as shown in Fig. E6.1a(a) and Fig. E6.1a(b). The curvature of the cylinder does not change the concept and mechanism of drag flow. Next, the stationary surface must be created. The simplest solution is to place the solid cylinder inside a stationary barrel, as in Fig. E6.1a(c) and Fig. E6.1a(d), where in addition we created entrance and exit ports through the barrel separated by a solid obstruction. 

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