Acceleration, centrifugal separation

Phase Separation. An approximate estimation of phase separation may be obtained visually. In general, creaming, flocculation, and coalescence have occurred before phase separation is visible, thus sometimes making quantitative evaluations more difficult. Accelerating the separation by centrifugation followed by appropriate analysis of the specimens may be useful to quantitatively determine the phase separation. Details on mechanisms of creaming and phase separation as well as some advances in the monitoring techniques of emulsion stability have been reviewed by Robins [146]. 

The terminal settling velocity u, for a single spherical particle in a centrifugal separator can be calculated from equation 9.5 with the centripetal acceleration rto2 replacing the gravitational acceleration g to give... 

Figure 8.7 External field suppression of the role of centrifugal barriers in outgoing reaction channels. The incoming collision channels are shown by the full curves the outgoing channels - by the dashed curves. An applied (magnetic or electric) field separates the energies of the initial and final channels and increases the kinetic energy of the particles in the outgoing collision channels, thus accelerating their separation. Adapted from Ref. [91] Copyright 2005.

In the case of a centrifugal separator (i.e., a centrifuge), the acceleration due to centrifugal force, which should be used in place ofg, is given as ra>, where r is the radial distance from the central rotating axis (m) and co is the angular velocity of rotation (radian s -). Thus, the terminal velocity Vj (ms ) is given as... 

A number of techniques are used commercially to accelerate emulsion breakdown. Mechanical methods indude centrifugal separation, freezing, distillation and filtration. Another method is based on the principle of antagonistic action - i.e. the addition of O/W-promoting emulsifiers tends to break W/O emulsions, and vice-versa. Emulsions can also be broken by the application of intense electrical fields, the principal factors involved being electrophoresis in the case of O/W emulsions and droplet deformation in the case of W/O emulsions. 

The cyclone or centrifugal separator is a device utilizing radial acceleration for separating partides suspended in a gas stream. It con-... 

The molecules of both HSl and HS2 have a high colloid stability due to their very low collision efficiency and small size which prevent them from settling under normal gravitational acceleration. Their separation in a centrifuge with a g value of some thousands is still practically inefficient. This fact is used for sedimentation analysis to investigate the destabilization and aggregation rate of the coagulation process of humic substances. 

Example 7-1. (a) Estimate the terminal velocity for 80-to-100-mesh particles of limestone (pp = 2800 kg/m ) falling in water at 30°C. (b) How much higher would the velocity be in a centrifugal separator where the acceleration is 50gl... 

To evaluate the performance of a centrifugal separation process, a dimensionless separation factor, SF, defined as the ratio of centrifugal acceleration to gravitational acceleration, is used... 

A centrifuged separator consists of a rotating bowl or basket into which the materials to be separated are fed. One type, operating by filtration, uses a perforated basket on which the solids are retained while the liquid passes through. The other uses a solid basket or bowl against which the solids deposit, while the liquid remains close to the center and is withdrawn over a dam. This latter type operates by accelerated settling and decantation and is also used for the separation of immiscible liquids. 

In the centrifugal separation, the centrifugal acceleration in a circular motion can be represented by equation 2.8 ... 

Introduction. Centrifugal separators make use of the common principle that an object whirled about an axis or center point at a constant radial distance from the point is acted on by a force. The object being whirled about an axis is constantly changing direction and is thus accelerating, even though the rotational speed is constant. This centripetal force acts in a direction toward the center of rotation. 

Example 4-2 Solid particles (average density of 2800 kg/m ) are settling in water (30°C). What is the terminal velocity for the particles Also, what would be the velocity of the system in a centrifugal separator with an acceleration of 390 m/sec ... 

---