Centrifugation, pressure effects

Extensive application of the theory has been made in treating pressure effects on velocity centrifugation. If w denotes angular speed, sp the sedimentation coefficient at pressure p, ra the radius of the meniscus, x = (r/ra)2, the usual representation of pressure effects leads to the relation (10),... 

The process permits the treatment of either bulk concentrate or freshly extracted juice. Freshly extracted juice is first stabilized at 175°-180°F (79.4°-82.2°C) then centrifuged in a high speed centrifuge to effect a pulp reduction to 2% to inhibit development of excessive back pressures in the column due to plug-... 

It does not matter, from the fundamental point of view, how the pressure drop is generated in the filter. In the case of the centrifugal filters there is an additional phenomenon of the mass forces acting on the Hquid within the cake. The conventional filtration theory must be amended to include this effect (2). 

In pressure diffusion, a pressure gradient is estabUshed by gravity or in a centrifugal field. The lighter components tend to concentrate in the low pressure (center) portion of the fluid. Countercurrent flow and cascading extend the separation effect. 

A second type of apparatus based on the pressure diffusion effect is the separation nozzle. Pressure gradients in a curved expanding jet produce an isotopic separation similar to that in a centrifuge. The separation effect obtained with a single jet is relatively small, and separation nozzle stages, similar to gaseous diffusion stages, must be used in a cascade to realize most of the desired separations. 

Mass Transport. An expression for the diffusive transport of the light component of a binary gas mixture in the radial direction in the gas centrifuge can be obtained directly from the general diffusion equation and an expression for the radial pressure gradient in the centrifuge. For diffusion in a binary system in the absence of temperature gradients and external forces, the general diffusion equation retains only the pressure diffusion and ordinary diffusion effects and takes the form... 

The two principal elements of evaporator control are evaporation rate a.ndproduct concentration. Evaporation rate in single- and multiple-effect evaporators is usually achieved by steam-flow control. Conventional-control instrumentation is used (see Sec. 22), with the added precaution that pressure drop across meter and control valve, which reduces temperature difference available for heat transfer, not be excessive when maximum capacity is desired. Capacity control of thermocompression evaporators depends on the type of compressor positive-displacement compressors can utilize speed control or variations in operating pressure level. Centrifugal machines normally utihze adjustable inlet-guide vanes. Steam jets may have an adjustable spindle in the high-pressure orifice or be arranged as multiple jets that can individually be cut out of the system. 

In the friction layer where the isobars are curved, the effect of frictional drag is added to the forces discussed under gradient wind. The balance of the pressure gradient force, the coriolis deviating force, the centrifugal force, and the frictional drag in the vicinity of the curved isobars results in wind flow around low pressure and high pressure in the Northern Hemisphere, as shown in Fig. 17-16. 

Centrifugal compressors in general are used for higher-pressure ratios and lower-flow rates compared to lower-stage pressure ratios and higher-flow rates in axial compressors. Figure 6-3 is a map for centrifugal compressors that shows the effect of specific speed (A ) and specific diameter (Z) ) on their... 

Klassen, H.A., Effect of Inducer Inlet and Diffuser Throat Areas on Performance of a Low-Pressure Ratio Sweptback Centrifugal Compressor, NASA TM X-3148, Lewis Research Center, January 1975. 

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