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Section summary |
---|

1. Definition |

2. Calculation |

3. Usage |

The air flow is a fundamental data in pneumatic
conveying systems. From the air flow, the air
speed, solids loading ratio,
pressure drop...
can be calculated. It must however be noted that the air flow is
usually given in normal conditions (Nm^{3}/h) not necessary
representative of the conditions in the conveying line as the air is
compressible. The objective of this page is to show how to calculate
the air volumetric flowrate at different conditions and calculate as
well the mass flowrate.

How to calculate volumetric air flow ? How to calculate mass air flow ?

From the volumetric air flowrate given in conditions 1 (**often
the normal conditions, 101325 Pa and 20°c**), the volumetric
flow can be calculated in conditions 2. Conditions 2 should be
either the beginning of the line or the end of the line.

The pressure in conveying line is not very high, few bar abs at maximum, thus the perfect gas law applies well.

Throughout the line, the number of moles of air / h is conserved, so the following equality can be written :

**Equation 1 : calculation of the air volumetric flowrate at
different conditions
**

With :

- Q- Q

- P1 = pressure in conditions 1 (Pa)

- P2 = pressure in conditions 2 (Pa)

- T1 = temperature in conditions 1 (K)

- T2 = temperature in conditions 1 (K)

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**To calculate the air mass flowrate, it is necessary to calculate
the air volumetric mass at the conditions studied**. It can also
be defined thanks to the perfect gas law.

With :

- ρ

- P = pressure at the conditions considered (Pa)

- T = temperature at the conditions considered (K)

- M

The volumetric mass can thus be multiplied by the volumetric flowrate to get the air mass flowrate in the pneumatic conveying pipe :

With :

- m

- Q

ρair = volumetric mass of the air at the conditions considered (kg/m

The following data can be calculated from the air volumetric flowrate and air mass flowrate

- Air conveying velocity at any point of the line

- Air solids ratio

- Pressure drop in pipes

Examples of calculation and conversions can be see on the page dedicated to the shortcut design method for calculation of dilute phase pneumatic conveying lines.