Centrifuges sigma value

The sigma value is the equivalent area of a gravity settler that would perform the same separation as the centrifuge. 

Sigma values and scale-up of centrifuges. A useful physical characteristic of a tubular-bowl centrifuge can be derived by multiplying and dividing Eq. (14.4-12) by 2g and then substituting Eq. (14.3-9) written for Dp into Eq. (14.4-12) to obtain... 

For the conical conveyor type centrifuge the Sigma value can be calculated as (see Figure 7.7 for dimensions)... 

For the conocylindrical conveyor-type centrifuge the Sigma value is usually assumed to be the sum of the values for a true cylindrical section of length L given by equation 7.17 and for a conical section of length Li thus... 

The use of conical discs, or angled vanes, on the conveyor will theoretically enhance the Sigma value, the clarification capacity, of the centrifuge. To estimate the Sigma value of a stack of conical discs, the formula used for disc stack centrifuges may be employed [11] ... 

The total Sigma value for the centrifuge is obtained by adding Eo to the Sigma value calculated for the conveyor section between the feed zone and the discs. 

It is shown in Section 4.3.1 that the clarification capacity of a decanter is the product of the Stokes settling velocity (equation (4.28)) and the Sigma value of the centrifuge (equation (4.32)). The Stokes velocity is a function of the process material s physical parameters, while Sigma i.s a function of mechanical features of the centrifuge. 

The Sigma value for the decanter normally would be obtained from the decanter manufacturer, but for demonstration purposes a value will be estimated here. From equation (4,8). centrifuge gdevel ... 

The effective area of the centrifuge, known as the Sigma value, S, is obtained by integration of equation 4.18, as follows. 

If the two centrifuges are arranged in parallel, each one takes one half of the total flow, Q, and the performance is compared with that of one centrifuge taking the whole of the flow. In terms of cut size, the Sigma theory (see section 7.2.2) can be used to write for the same machine (same S value) ... 

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