Cyclone Flow Pattern and Pressure Drop

Predicting the separation efficiency of cyclones involves predicting how particles behave in the separation space. In order to do this, we need to know the velocity distribution of the gas. Some researchers have made all-embracing models for both gas flow pattern and separation efficiency others have concentrated on one or the other. We look at the two issues separately here. 

Models for cyclone pressure drop sometimes spring from models for the flow pattern and are based on an estimation of the actual dissipative losses in the cyclone others are purely empirical. 

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Cyclone Flow Pattern and Pressure Drop Px veos ... 

Flow pattern and pressure drop in cyclone dust collectors. Ibid., 31 972-984. 

This completes om short discussion of flow pattern and pressure drop. We now tmn to the models. By far most of the modeling work has concentrated on cyhnder-on-cone cyclones with tangential inlets. We will therefore talk of cyclones in these sections. Very little direct work on the modeling of the flow pattern and the pressure drop in swirl tubes has been published our... 

The Reynolds stress model requires the solution of transport equations for each of the Reynolds stress components as well as for dissipation transport without the necessity to calculate an isotropic turbulent viscosity field. The Reynolds stress turbulence model yield an accurate prediction on swirl flow pattern, axial velocity, tangential velocity and pressure drop on cyclone simulation [7,6,13,10],... 

The flow pattern of the vortex motion of the gas in reverse-flow cyclone is quite complex. First, it is three-dimensional second, the flow is turbulent An exact analysis is therefore difficult Soo (1989) has summarized a fundamental analysis of velocity profiles and pressure drops in such a cyclone. He has also analyzed the governing particle diffusion equation in the presence of electrostatic, gravitational and centrifugal forces. He has then provided an analytical expression for partide collection efficiency under a number of limiting conditions. We wiU, however, opt here for a much simpler model of particle separation in a cyclone developed by Clift et id. (1991). This approach is based on a modification of the original model by Leith and Licht (1972). The model will be... 

Performance of a cyclone separator is determined by flow pattern, pressure drop, and collection efficiency. 

But, with the above ideas about the nature of cyclone pressiu-e drop and some simplistic considerations, we can see intuitively, as shown below, that cyclone pressure drop, indeed, should decrease with increasing wall fraction in the body (we will also present a macroscopic quasi-theoretical model of cyclone performance with predicts such effects later in this book). Consider two extremes for the flow pattern in the cyclone body ... 

This completes our treatment of the models for the flow pattern in the cyclone. We discuss one more model for vg, namely that of Meissner and Loffler (1978), in Appendix 4.B. We now examine some of the most used pressure drop models. 

Thus, although this model was derived by considering the gas flow pattern in the cyclone, it relates, in its final form, the separation cut-point diameter, X50, to the pressure drop. Hence, the pressure drop needs to be predicted to use the model. A good pressure drop model for this purpose is that of Shepherd and Lapple, Eq. (4.3.18). 

We have examined some of the most widely acclaimed and cited cyclone models. There is one more way of predicting the flow pattern, pressure drop and the separation efficiency in cyclones and swirl tubes, however by Computational Fluid Dynamics, or CFD for short. 

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