Flow Classifications There are a variety of different methods to classify flows in pneumatic conveying. These graphical depiction are meant to help us understand and visual the process of conveying.

Geldart Classification One of the common classifications of particles and powders in motion is the Geldart classification. This classification using the density difference between the solid particles and the gas plotted against the diameter of the particle. The density is give in g/cm3 and the particle size in micron units.

Geldart Classification

Geldart’s Classification A ρp<1.4 g/cm3 small Dp B ρp<1.4 to 4.0 g/cm3 (sand like) 40-500 µm C cohesive smaller Dp D large particles - dense

General Zenz type diagram

The Particle Reynolds Number is often used in classifications The Particle Reynolds Number is often used in classifications. The diameter is the particle diameter.

Parameters for Generalized Plot

Attempt to have one operating point for the pneumatic conveying representation The generalized plot of the pressure drop per unit length against the Reynolds number presents the condition at only one point in the conveying line. As the velocity increases with distance down the pipeline, the Reynolds number moves to the right. If one employs the product of gas density times the gas velocity, only one operating point is seen for the whole system.

General Phase Diagram for One Operating Point Pressure Drop/L Gas Density * V

Clustering? The phenomena of particles clustering together and behaving more like a group of particles instead of a single particle has been often conjectured. A experiment that points to this process is seen next with the gas velocity was varied over a wide range from high to low approaching or being at the saltation point for the flow.

Clustering Process The following plot shows the maximum in the data for pressure drop per unit length with the gas velocity. The two single theoretical curves are for large and smaller particle. The experimental plot for the smaller particles show how at higher velocities the particles behave like large particles and for lower velocities how they transition into the smaller particle behavior.

Clustering Possibilities

Transitions in Vertical Pneumatic and Fluidized Bed Flows Leung has shown two pathways for particle to transition between low and high gas velocities in vertical tubes or pipes. Which path the material follows depends on the particle properties.

Choking is a phenomena that arises in vertical flow when the energy is not sufficient to sustain a steady flow of materials an thus chokes. Yang has explored this region and developed a correlation

Yang Coking Criteria

Wypych’s Friction Function Wypych has work on a friction function in order to describe pneumatic conveying of solids. He found this technique particularly in the moving wave transport of solids.

Another way of representing the friction function and the pressure drop is in a cross plot