The conveying air velocity is the speed at which air circulates in the conveying pipe of a pneumatic conveying line. Air velocity is changing all along the conveying line, thus one must always refer to a reference position (beginning or end of the line) when calculating the air velocity. The air velocity is sometimes called conveying speed.
The air velocity in the pipes is calculated by dividing the air volumetric flowrate (m3/s) by the passing section of the pipe (m2).
Equation 1 : calculation of the air velocity in a conveying pipe of diameter D
With :- uair = air velocity in conveying pipe of diameter D (m/s)
Note the following : the air volumetric flowrate is changing with the pressure and temperature, along the conveying line pressure is decreasing thus air expands, which makes the volumetric flowrate higher and thus the conveying air velocity higher (at constant D). To counter this phenomena, it is possible to change the diameter of the pipe, thus D may not be constant all along a same pipe.
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Every conveying line is unique and will have its specific air velocity, however, some orders of magnitudes can be given for both dilute and dense phase.
Table 1 : Reference end of line
velocity for dilute and dense phase conveying
|Type of conveying||Pressure||Vacuum|
||20-25 m/s||20-30 m/s
Note that the actual velocity of the product conveyed is lower than the conveying air velocity.