Executive summary
In this work our objective has been to develop quantitative methods for the prediction of all technically important features of the flow of gas and solid particles through ducts. Flows of this sort are of great importance in pneumatic transport of particulate material and in the circulation of particulate materials within certain chemical process plants; for example, catalytic crackers used in oil refining, and circulating fluidized beds, which are important in coal processing and a number of other chemical processes. Design of these systems is made difficult by the tendency of the particles to distribute themselves over the cross section of the duct in a highly non-uniform way. Consequently it has not been possible to predict properties such as the holdup of particles, the distribution of residence times of the particles in a given section of duct, or the gas pressure drop. Even scaling these quantities between ducts of different sizes, operated under different conditions, has been uncertain, at best.
In an earlier period of IFPRI funding (see Final Report FRR 09- 10) we developed equations of motion for gas-particle mixtures and applied them to streamline flow through ducts. The results predicted a rich variety of behavior, which conformed well with observations in systems of this type, but the quantitative predictions were unrealistically sensitive to the values of,‘certain parameters representing physical properties of the particles. We speculated that this shortcoming was a consequence of limiting our attention to steady, streamline flows since, in most situations of technical interest, the flow is markedly unsteady, like the fast, turbulent flow of a simple liquid or gas through a pipe. Accordingly, we have extended our treatment to cover this type of flow, and we now find that the unrealistic sensitivity is suppressed, while the qualitative features of interest are conserved. There is a shortage of experimental measurements against which the quantitative predictions can be tested, but comparisons with the data presently available in the open literature are encouraging.