Solids Particle Velocity in pneumatic conveying (dilute phase)

Section summary
1. Definition
2. Calculation
3. Usual values for dilute phase pneumatic transport

Pneumatic Transport
Types of pneumatic transport
Conveying phases
Dilute Phase transport
Dense Phase transport
Air mover
Roots Blower
After Cooler
Airlock Rotary Valve
Product inlet / Injector
Piping
Pick-up velocity
Conveying speed / velocity
Air volumetric and mass flowrate
Pipe Equivalent Length
Solids velocity in pipe
Bends
Solids Breakage
Pressure drop
Pipe Diameter or Bore
Design methods
Pipe Blockage
Powder Build-up
Selecting dilute or dense phase
Horizontal Conveying
Vertical Conveying

1. Definition

During the pneumatic transport of a powder in a pneumatic conveying line, the air is bringing the energy necessary to move the solids all along the pipe. Air velocity can be calculated easily thanks to the air flowrate and pipe diameter but it would be wrong to assume that the solid speed in the pipe is equal to the conveying air velocity, particularly in dilute phase. Indeed, the particles of solids won't be carried out all the way at the same velocity than the air as the particles will resist the air flow (drag), bounce on the pipe walls, settle... which will slow them down. As a consequence the particle conveying velocity will be less than the air conveying velocity. The factor in between the 2 velocities is called slip factor.

2. Calculation

The particle conveying velocity is calculated from the air conveying velocity thanks to the slip factor :

Particle velocity calculation equation with slip factor

Equation 1 : calculation of the particle conveying velocity

With :
- uair = air velocity in conveying pipe (m/s)
- up = solid particles conveying velocity (m/s)
- fslip = slip factor


3. Usual values for dilute phase conveying

Typical values of slip factors and thus of solid particles conveying velocity can be found in litterature.

Table 1 : Usual values of slip factors

Particle Slip factor
Coarse particle
0.8
Fine powder
0.9

Source : Theory and Design of pneumatic conveying Systems, Agarwal, Powder Handling and Processing, 2005.




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