Solids Particle Velocity in pneumatic conveying (dilute phase)

Do you have a question, a remark ? Please contact the author at

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

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

Straight pipes

Typical values of slip factors and thus of solid particles conveying velocity can be found in litterature [1].

Table 1 : Usual values of slip factors

Particle Slip factor
Usual range all kinds of particles
Coarse particle
Fine powder


In 90 degrees bends, the solids slow down further and the exit velocity is equal to around (0.8*entry velocity). It takes around 20 pipe diameters to reaccelerate the solids after the bend.

This last relationship explains also why it is important not to have consecutive bends in a pipe layout : the solids will slow down and finally deposit, which may choke the line.

Source : [1] Theory and Design of pneumatic conveying Systems, Agarwal, Powder Handling and Processing, 2005.

Do you want to know more ? is covering all aspects of solids and powder processing and handling
The pages below will probably interest you !
Answers ALL your questions on solids and powder mixing
All you need to know about measuring the degree of mixing (Coefficient of Variation) of a dry mix
All on the physical phenomena causing segregation of particles and how to avoid them
All on main size reduction processes, key equipement, design consideration..etc..
POWDER Properties
All on powder key physical characteristics, among others : flowability, density...etc..
All equipment found in bulk solids handling industries, explained, with design tips...
You can find much more through the menus at the top of the page !