B The Meissner and Loffler Model

First we calculate the wall velocity using an a of 0.723 which we compute from Eq. (4.2.5). This gives ve = 31.5 m/s, which is slightly higher than Vin due to the constriction of the inlet jet in the slot inlet. We can then calculate vecs from (4.2.6), calculating the friction factor, /, from (4.2.9)  

Note that we divide the solids loading in kg dust/m air with the air density to obtain the loading as a mass fraction. This gives vgcs = 64.1 m/s. 

We now have all the necessary data. Inserting in equations (4.3.3) and (4.3.4) using the value of K for a rounded edged vortex tube, we find that Barth predicts a pressure drop of  

Obviously the predictions of the models differ considerably. While the models of Stairmand and Shepherd and Lapple agree reasonably well, the Casal/Mar-tinez and Barth models differ by almost a factor of two. In the following chapter we shall put the models for pressure drop to a test we shall compare their predictions of the effect of cyclone length on pressure drop with experiment. 

They consider a cylindrical element as sketched. Convective flow of moment-of-momentum in and out of the element is balanced with the moment of the wall friction force at the top and bottom walls. An obvious weakness in this approach is that the friction at the cylindrical part of the waU is not easily included. Meissner and Loffler therefore propose a three-step strategy  

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