Cross-flow centrifugal

Pharmaceutical Removal of suspended matter is a frequent application for MF. Processes may be either clarification, in which the main product is a clarified liquid, or solids recovery. Separating cells or their fragments from broth is the most common application. Clarification of the broth in preparation for product recovery is the usual objective, but the primary goal may be recovery of cells. Cross-flow microfiltration competes w l with centrifugation, conventional filtration by rotary vacuum filter or filter press and decantation. MF delivers a cleaner permeate, an uncontaminated, concentrated cell product... 

Figure 4.15. Solid-liquid separation in industrial scale using centrifugation in continuous mode (A) or passage of the suspension through manifolds such as those shown in (B) mounted with filter cartridges (C) designed for tangential or cross-flow of liquid suspension. Panel A NIH Fredrick facility, with permission Panels B and C Milipore, MA, with permission.

The collection of particles is achieved in a countercurrent flow between the water droplets and the particulates. In a cyclonic scrubber, water is injected into the cyclone chamber from sprayers located along the central axis, as shown in Fig. 7.19. The water droplets capture particles mainly in the cross-flow motion and are thrown to the wall by centrifugal force, forming a layer of slurry flow moving downward to the outlet at the bottom of the cyclone. Another type of scrubber employs a venturi, as shown in Fig. 7.20. The velocity of the gas-solid suspension flow is accelerated to a maximum value at the venturi throat. The inlet of the water spray is located just before the venturi throat so that the maximum difference in velocity between droplets and particles is obtained to achieve higher collection efficiency by inertial impaction. A venturi scrubber is usually operated with a particle collector such as a settling chamber or cyclone for slurry collection. 

Based on these considerations, a schematic was proposed showing regions of vortices and of secondary cross flow in the T-junction by which the findings given above can be explained (see Figure 1.57) [68], This is said to resemble secondary flow of Prandtl s first kind as a result of centrifugal force when fluid flows in curved path. 

The existence of spiral flow is observed near the short radius of the bend. The water surface is superelevated at the outside wall for the cylindrical free vortex. The element EF is subjected to a centrifugal force mV2/r, which is balanced by an increased hydrostatic force on the left side due to the superelevation of the water surface at C above that at D. The element GH has exactly the same hydrostatic force inward, but the centrifugal force outward is much less because the velocity is decreased by friction near the bottom. This results in a cross flow inward along the bottom of the channel, which is balanced by an outward flow near the water surface, hence the spiral. This spiral flow is largely responsible for the commonly observed erosion of the outside bank of a river bend, with consequent deposition and building of a sand bar near the inside bank. 

Vortex filters use centrifugal force to swirl raw water above the surface of the media in a cross-flow manner. Large suspended solids are collected on the sidewall of the filter tank. The smaller solids drop down to the surface of the fine sand media and are filtered out through this media. When the pressure drop reaches about 15 psig, the vortex filters are backwashed. 

Table 1. Relationship between X and the physical solute properties using different FFF techniques [27,109] with R=gas constant, p=solvent density, ps=solute density, co2r=centrifugal acceleration, V0=volume of the fractionation channel, Vc=cross-flow rate, E=electrical field strength, dT/dx=temperature gradient, M=molecular mass, dH=hydrodynamic diameter, DT=thermal diffusion coefficient, pe=electrophoretic mobility, %M=molar magnetic susceptibility, Hm=intensity of magnetic field, AHm=gradient of the intensity of the magnetic field, Ap = total increment of the chemical potential across the channel...

Cross-flow MF Pall PSS (2.5 pm limit of separation), Fairey Microfilfrex FM4 (1 pm) and APV Ceraver (1.4 pm) ceramic and stainless steel membranes SpinTek ST IIL centrifugal membrane filtration technology... 

Heal JM, Bailey G, Helphingstine C, Thiem PA, Leddy JP, Buchholz DH, Nusbacher J. Non-centrifugal plasma collection using cross-flow membrane plasmapheresis. Vox Sang 1983 44(3) 156-66. 

Further, it is possible to utilize different fields to yield the various FFF subtechniques. The two most common fields are centrifugal and fluid cross-flow, which give rise to the sedimentation and flow FFF subtechniques. Other fields currently in use include thermal, electrical, and magnetic fields. In the normal mode, it is possible to extract physical parameters from retention data. For example, sedimentation FFF using a centrifugal force gives information about the buoyant mass, and flow FFF gives information about the sample s diffusivity or hydrodynamic diameter. 

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