Re: Conveyance Velocity
Dear Ken,
Assuming that this thread is about pneumatic conveying of materials.
Some literature (Vacuum Line Loss Charts) show different minimum and maximum recommended velocity ranges for horizontal lines and vertical upflow lines. The upflow velocities are shown higher than the horizontal flow velocities. Other charts don't make this distinction between horizontal and vertical flow and just show a single velocity range.
In pneumatic conveying, the gas velocity in horizontal lines is chosen at a higher value than for vertical lines.
This is due to the fact that the gravity in horizontal lines is perpendicular to the material flow.
In order to keep the particles in suspension, a higher velocity is required.
Some literature states: "the minimum conveying air velocity for flow vertically up is generally lower than that for horizontal flow." This contradicts the two recommended velocity ranges shown on the charts mentioned above.
This statement is correct.
Some charts show the velocity range is constant no matter what tube diameter and others show the recommended conveyance velocities increasing with increasing tube diameter.
The conveying air velocity cannot be kept constant as the suspension velocity is decreasing with the square root of the gas pressure.
This means that the gas velocity at the end of a pipeline has to be higher, due to the lower gas pressure at the end of the pipeline.
Some literature give velocity ranges for different material types and air retention properties. The charts don't make this distinction in material types.
It is obvious that the required gas velocity is different for different materials.
The different suspension velocity for different materials require different gas velocities, to keep those materials in suspension.
See attached PDF for Example.
This chart seems to be for gas only situations.
What are the general rules for Conveyance Velocity and where can specific information be found?
The (local) gas velocity must be a factor times the (local) suspension velocity, in order to prevent sedimentation.
Have a nice day ■
Teus
Conveyance Velocity
I am confused on the different information available on conveyance velocity. Please help clarify.
Some literature (Vacuum Line Loss Charts) show different minimum and maximum recommended velocity ranges for horizontal lines and vertical upflow lines. The upflow velocities are shown higher than the horizontal flow velocities. Other charts don't make this distinction between horizontal and vertical flow and just show a single velocity range.
Some literature states: "the minimum conveying air velocity for flow vertically up is generally lower than
that for horizontal flow." This contradicts the two recommended velocity ranges shown on the charts mentioned above.
Some charts show the velocity range is constant no matter what tube diameter and others show the recommended conveyance velocities increasing with increasing tube diameter.
Some literature give velocity ranges for different material types and air retention properties. The charts don't make this distinction in material types.
See attached PDF for Example.
What are the general rules for Conveyance Velocity and where can specific information be found?
Attachments
example vacuum line loss chart (PDF)
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