(10b) A New Theoretical-Empirical Model for Cyclone Design

One of the theoretical bases for many cyclone design methods is the work of E. Feifel. One of those who continued and improved upon Feifel’s work was G. Miczek. Although some of Miczek’s work was published (two in Czechoslovakia and one in Chem. Eng. in conjunction with C. Doerschlag), most was not, and has been held as proprietary by my current (and past) businesses for commercial benefit. After 40 years of work within this field, benefitting from Miczek’s work, I wish to give credit to Miczek for his work by sharing it with the scientific and industrial communities.

The method is initially based upon the Vortex Theory described by Feifel and others. This describes a vortex of maximum tangential velocity at some radius that is a function of the over-all geometry of the cyclone. While the diameter of the cyclone itself is a variable that affects the location and magnitude of this “Core Vortex” velocity, it is, contrary to popular belief, by no means the most significant variable. The Core Vortex velocity magnitude and position is more strongly a function of the inlet size, arrangement and location, as well as the gas outlet diameter. The magnitude of the Core Vortex tangential velocity is not only the primary measure of the inertial forces available for particle separation but also the primary contributor to cyclone pressure drop.

At the highest level, there are two primary methods for increasing cyclone separation efficiency:

1. Increase the centrifugal force (defined as the opposite of centripetal force): i.e. increase the tangential velocity at a given radius or decrease the radius at a given tangential velocity of the flow stream that is transporting the particle.
2. Provide for a greater amount of time for the particle to be transported to the collection point before the flow stream exits the cyclone.

Miczek’s contributions can be summarized as a method that determines what he calls a “Specific Flowrate” for any given cyclone. This Specific Flowrate should be more properly defined as Specific Velocity which is defined as the average one directional gas flow velocity of a cyclone at some defined standard conditions. These standard conditions include the pressure drop across the cyclone. This approach of comparing Specific Velocity of various cyclones at standardized conditions and pressure drop allows for a description of “cyclone quality” that considers the cyclone pressure drop, capacity, Core Vortex Velocity and radiuses well as a measure of the cyclone residence time.

While cyclones are relatively simple to construct, the accurate prediction of their performance remains quite challenging and difficult for most engineers. By combining Miczek’s theoretical model with the empirical corrections he developed, an accurate predictive model for cyclone pressure drop and fraction efficiencies was achieved. We have been able to refine and improve the coefficients of Miczek’s empirical corrections as we have successfully designed hundreds of cyclones used in commercial and research applications with minimal error in predicted pressure drop and fraction efficiencies. The intent of this paper is to describe in detail the theory, research it is based upon, and provide guidance for the continued refinement of the empirical coefficients by others who wish to utilize this method.