Relative centrifugal field

The force produced in a rotating body is given as multiples of earth s gravitational field (9.807 m/s ), and relative centrifugal field (ref) is calculated by... 

The correct term to describe the force required to separate two phases in a centrifuge is relative centrifugal force (RCF), also called relative centrifugal field. Units are expressed as number of times greater than gravity (e.g., 500 X g). 

The final and less commonly dealt-with member of the family of electrokinetic phenomena is the sedimentation potential. If charged particles are caused to move relative to the medium as a result, say, of a gravitational or centrifugal field, there again will be an induced potential E. The formula relating to f and other parameters is [72, 77]... 

If the motion of the molecule is one of translation, as it is during sedimentation in a centrifugal field, the velocity of every bead is the same, and in the free-draining case the difference in velocity Aw, for each bead relative to the solvent is the same as the (relative) translational velocity u of the molecule as a whole. Fig. 138 is illustrative of this case. The total force on the molecule is then... 

The flow problems considered in Volume 1 are unidirectional, with the fluid flowing along a pipe or channel, and the effect of an obstruction is discussed only in so far as it causes an alteration in the forward velocity of the fluid. In this chapter, the force exerted on a body as a result of the flow of fluid past it is considered and, as the fluid is generally diverted all round it, the resulting three-dimensional flow is more complex. The flow of fluid relative to an infinitely long cylinder, a spherical particle and a non-spherical particle is considered, followed by a discussion of the motion of particles in both gravitational and centrifugal fields. 

It is the aim of this section to offer but a brief introduction to this relatively new field of endeavour that will surely have a not inconsiderable role in shaping the whole future of both physical and chemical processing. It may be noted at the outset, however, that it is not the use of centrifugal forces which is a relatively new development, but rather their application in spinning discs and indeed, centrifugal devices are already widely used in processing, as indicated by the following examples ... 

The gravitational force in a centrifuge is dependent on two quantities the speed of rotation and the distance from the centre of rotation. Equation 4.12 expresses the relative centrifugal force (RCF) (in units of g - the Earth s gravitational field) in terms of these two parameters. 

The relative centrifugal force (RCF) is defined as the force field relative to the Earth s gravitational field Equation 13.2 shows its definition ... 

A more useful concept is the relative centrifugal force (RCF), which is the force acting on a given particle in a centrifugal field in terms of multiples of its weight in the earth s gravitational field, and... 

Equilibrium separation. When a gas mixture in a centrifuge rotates as a solid body without motion relative to the wall of the cylinder, its pressure and composition are independent of 6 and 2 and vary with r according to the equations for equilibrium in a centrifugal field. 

Unlike sedimentation equilibrium methods, measurement of sedimentation rates - how fast the molecules fall in the centrifugal field -can give information about both macromolecular shape and the size. These methods use relatively high centrifugal forces and measure the concentration profiles within the centrifuge tube (cell) as a function of time. 

Following cell homogenization, centrifugation techniques enjoy nearly universal use in the purification of subcellular organelles. Centrifugation is relatively simple and can be performed on several liters to submilliliter volumes of cell homogenate. As shown in Equation 20.1, the sedimentation velocity dx/dt per unit centrifugal field (m x) is dependent on the size of the particle (r ), the density difference of the particle compared to the medium (pp - p ), and the viscosity of the medium (tj) ... 

Sedimentation works against diffusion caused by Brownian motion. With a sufficiently weak centrifugal field (relative to particle and density differences), a stage will be reached where the rate of sedimentation equals the rate of diffusion, and a state of equilibrium sedimentation occurs. For given experimental conditions, the sedimentation equilibrium depends on the mass of the dissolved molecule and is therefore a method for determining molecular weights. 

Most of the early methods developed for probing the relative stability of asphaltene and crude emulsions were centered on monitoring the amount or percentage of an emulsion which will phase separate on a macroscopic scale into a bulk continuous or disperse phase under the influence of gravity or a centrifugal field. These experiments are usu-... 

Despite many potential advantages of centrifugal fields, there are relatively few examples of... 

Here, g is the gravitational acceleration, z is the height of the particle measured relative to the bottom of the column in the case of the gravitational field or the distance from the axis of rotation in the case of a centrifugal field, and w is the angular velocity of rotation of the centrifuge. In general, g depends on the distance from the center of the earth. However, since //is very small compared to the radius of the earth, one can assume... 

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