Pneumatic Transports

Overview

Engineering reference data for Pneumatic Transports in miscellaneous.

Key Formulas

Unit Conversion

$y = x \cdot k$

Multiply by conversion factor.

Linear Interpolation

$y = y_1 + \frac{(x - x_1)(y_2 - y_1)}{x_2 - x_1}$

Estimate between two known points.

Percentage

$p = \frac{\text{part}}{\text{whole}} \times 100\%$

Part as fraction of whole.

Variables

Transport Phases

Pneumatic transport operates in two distinct flow regimes, each with different characteristics and applications:

Dilute Phase Transport

In dilute phase (lean phase) transport, particles are fully suspended in the gas stream. Key characteristics:

• Velocity: Gas velocity exceeds saltation (horizontal) or choking (vertical) velocity
• Solids loading ratio: Typically below 15 (kg solids/kg gas)
• Flow pattern: Uniform suspension with particles distributed across the pipe cross-section
• Pressure drop: Relatively high due to continuous particle acceleration and wall friction
• Applications: Suitable for most powders; preferred for friable or heat-sensitive materials due to lower residence time

Dense Phase Transport

In dense phase transport, particles move as plugs, slugs, or a fluidized bed:

• Velocity: Gas velocity below choking/saltation velocity
• Solids loading ratio: Can exceed 15–100+ (kg solids/kg gas)
• Flow pattern: Alternating plugs of dense material and gas pockets, or moving bed flow
• Pressure drop: Lower specific energy consumption per unit mass transported
• Applications: Best for abrasive or degradable materials; requires careful system design

Critical Velocities

Two critical velocities define the transition between transport regimes:

Choking Velocity (Vertical Transport)

The choking velocity is the minimum gas velocity required to maintain dilute phase transport in vertical pipes. Below this velocity:

• Particles begin to settle and form slugs
• Pressure fluctuations increase dramatically
• The system transitions to dense phase flow

Saltation Velocity (Horizontal Transport)

The saltation velocity is the gas velocity at which particles begin to settle from the suspension and deposit on the bottom of horizontal pipes. Key considerations:

• Always higher than choking velocity for equivalent conditions
• Increases with particle size and density
• Determines minimum operating velocity for horizontal runs

Design Considerations

References

• Original Source