Centrifuges scale

Regardless of the machine device, centrifuges are typically maintenance-intensive. Filters can be cheaper in terms of capital and maintenance and should be considered first unless centrifugal equipment already exists. Small facilities (<1000 liters) use filtration, since centrifugation scale-down is constrained by equipment availability. Comparative economics of the two classes of operations are discussed by Datar and Rosen (loc. cit.). 

Fig. 17 Micropattemed surfaces allow ultrahigh-throughput production of size-specified aggregates. Surfaces patterned were generated in (a) poly(dimethylsiloxane) (PDMS) with wells of (b) 100, 200, 400 and 800 pM. (c) Sections of PDMS textured with 400 pM wells were inserted into wells in a 24-well plate. A single-cell suspension of hESCs was dispensed into the microwells. After 24 h, the well contents were imaged, extracted and re-imaged, (d) Aggregates were formed only in the presence of 10 pM of the ROCK inhibitor Y-27632, in the presence or absence of centrifugation. Scale bars 400 pM [134]...

A cyUndrical or, preferably, a pear-shaped separatory funnel (Fig. II, 1, 5, e and d) of 10-15 ml. capacity is usually employed for the separation of immiscible liquids. For separations on a smaller scale, a dropper pipette may be used the upper layer is best removed with a bent pipette as in Fig. XII, 1,3. For liquids which tend to emulsify, centrifugation (a hand centrifuge is satisfactory) will usually produce a clean line of demarcation between two immiscible liquids. 

The scale-up of filtration centrifuges is usually done on an area basis, based on small-scale tests. Buchner funnel-type tests are not of much value here because the driving force for filtration is not only due to the static head but also due to the centrifugal forces on the Hquid in the cake. A test procedure has been described with a specially designed filter beaker to measure the intrinsic permeabiHty of the cake (7). The best test is, of course, with a small-scale model, using the actual suspension. Many manufacturers offer small laboratory models for such tests. The scale-up is most reHable if the basket diameter does not increase by a factor of more than 2.5 from the small scale. 

The Z-concept permits scale-up between sinulat centrifuges solely on the basis of sedimentation performance. Other criteria and limitations, however, should also be investigated. Scale-up analysis for a specified sohds concentration, for instance, requires knowledge of sohds residence time, permissible accumulation of sohds in the bowl, G level, sohds conveyabihty, flowabihty, compressibihty, limitations of torque, and sohds loading. Extrapolation of data from one size centrifuge to another calls for the apphcation of specific scale-up mechanisms for the particular type of centrifuge and performance requirement. 

AH of these equations work in the scale-up of geometricaHy similar centrifuges. The reduces the effect of rotational speed from CO to and... 

A number of special processes have been developed for difficult separations, such as the separation of the stable isotopes of uranium and those of other elements (see Nuclear reactors Uraniumand uranium compounds). Two of these processes, gaseous diffusion and gas centrifugation, are used by several nations on a multibillion doUar scale to separate partially the uranium isotopes and to produce a much more valuable fuel for nuclear power reactors. Because separation in these special processes depends upon the different rates of diffusion of the components, the processes are often referred to collectively as diffusion separation methods. There is also a thermal diffusion process used on a modest scale for the separation of heflum-group gases (qv) and on a laboratory scale for the separation of various other materials. Thermal diffusion is not discussed herein. 

Type of centrifuge Inside diameter, in Disk diameter, in/niimher of disks Speed, r/min 2, value, units of 10 fF Recommended scale-up factors"... 

These scale-up factors are relative capacities of centrifuges of the same type hut different sizes when performing at the same level of separation achievement (e.g., same degree of clarification). These factors must not he used to compare the capacities of different types of centrifuges, f Approaches 2.5 at rates helow mL/min. fLong howl configuration. 

Solid-Bottom Basket Centrifuges SmaUer-scale, solid-bottom batch basket centrifuges are available for small test samples, when the sample cannot tolerate mechanical handling or when the traces of solids remaining in a more automated centrifuge would be subject to decomposition or spoilage. 

It is known that the specific resistance for centrifuge cake, especially for compressible cake, is greater than that of the pressure or vacuum filter. Therefore, the specific resistance has to be measured from centrifuge tests for different cake thicknesses so as to scale up accurately for centrifuge performance. It cannot be extrapolated from pressure and vacuum filtration data. For cake thickness that is much smaller compared to the basket radius, Eq. (18-116 7) can be approximated by... 

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