The definition of the suspension velocity is the free fall velocity of a particle at standard air conditions. (0 degrC and 1 bara) or the upwards pipe gas velocity to keep a particle in suspension.
The suspension velocity of a particle changes along a pneumatic conveying pipeline as a function of SQRT(1/gas density) or # SQRT(1/gas absolute pressure)
The suspension velocity of a particle is important in the calculations of a pneumatic conveying system:
-The acceleration of a particle
A small particle with a low suspension velocity undergoes a higher acceleration.
-Sedimentation/choking
Bigger particles with a high suspension velocity will fall out of the gas flow sooner, forming sedimentation or even a plug, resulting in choking.
-The suspension velocity is causing a partial pressure drop, whereby small particles are easier to keep in suspension than bigger particles
This is the reason that small particles require lower gas velocities than bigger particles.
Although there are numerous articles describing the importance of the suspension velocity (related to the particle density and the particle size) the commonly used pneumatic conveying calculation algorithms do not account for the suspension velocity.
Instead of the calculated or measured suspension velocity, the unit of “pick-up velocity” is used to determine the required airflow.
This “pick-up velocity” is in most cases derived from laboratory tests and therefore valid for the tested material and particle size. (And the pipe size and pressure)
Knowing that the suspension velocity is a function of the gas density (absolute gas pressure and temperature), the “pick-up velocity” must also be a function of absolute gas pressure and temperature, for which must be accounted for in the calculations.
A pneumatic conveying calculation must check for the ratio suspension velocity/gaswallvelocity to determine the boundary of sedimentation /choking.
In addition, the particle suspension velocity I combination with the gas velocity, resulting in the relative gas velocity must also be accounted for and leads to the requirement that the particle velocity MUST also be calculated.
(If the gas velocity equals the particle velocity, the particle will fall out of the gas flow, because there is only gravity acting on the particle)
The above description shows that the suspension velocity of a particle MUST be accounted for in a pneumatic conveying calculation algorithm to determine the existence of wall sedimentation/choking and that the material particle velocity also MUST be calculated for that purpose. ■
Suspension velocity in pneumatic conveying calculations.
The definition of the suspension velocity is the free fall velocity of a particle at standard air conditions. (0 degrC and 1 bara) or the upwards pipe gas velocity to keep a particle in suspension.
The suspension velocity of a particle changes along a pneumatic conveying pipeline as a function of SQRT(1/gas density) or # SQRT(1/gas absolute pressure)
The suspension velocity of a particle is important in the calculations of a pneumatic conveying system:
-The acceleration of a particle
A small particle with a low suspension velocity undergoes a higher acceleration.
-Sedimentation/choking
Bigger particles with a high suspension velocity will fall out of the gas flow sooner, forming sedimentation or even a plug, resulting in choking.
-The suspension velocity is causing a partial pressure drop, whereby small particles are easier to keep in suspension than bigger particles
This is the reason that small particles require lower gas velocities than bigger particles.
Although there are numerous articles describing the importance of the suspension velocity (related to the particle density and the particle size) the commonly used pneumatic conveying calculation algorithms do not account for the suspension velocity.
Instead of the calculated or measured suspension velocity, the unit of “pick-up velocity” is used to determine the required airflow.
This “pick-up velocity” is in most cases derived from laboratory tests and therefore valid for the tested material and particle size. (And the pipe size and pressure)
Knowing that the suspension velocity is a function of the gas density (absolute gas pressure and temperature), the “pick-up velocity” must also be a function of absolute gas pressure and temperature, for which must be accounted for in the calculations.
A pneumatic conveying calculation must check for the ratio suspension velocity/gaswallvelocity to determine the boundary of sedimentation /choking.
In addition, the particle suspension velocity I combination with the gas velocity, resulting in the relative gas velocity must also be accounted for and leads to the requirement that the particle velocity MUST also be calculated.
(If the gas velocity equals the particle velocity, the particle will fall out of the gas flow, because there is only gravity acting on the particle)
The above description shows that the suspension velocity of a particle MUST be accounted for in a pneumatic conveying calculation algorithm to determine the existence of wall sedimentation/choking and that the material particle velocity also MUST be calculated for that purpose. ■
Teus