We consider that the flow regime is iso-volume or stationary
Mass flow = volume flow rate x density
Volume flow (m3 / s) = section (m²) x average velocity (m / sec)
Volume flow (m3 / s) = volume of fluid disposed (m3) / flow time (seconds)
- the losses are directly related to speed fluid section and therefore Size ducts .
For compressible fluids (gas or air):
The gas is compressible, it is possible to transform a volume of the same quantity of gas by compressing or changing the temperature. It becomes very difficult to speak of a quantity of gas volume without giving the pressure and temperature of gas at the time the volume was measured .. It would be difficult to give a temperature and pressure whenever there is talk of a volume of gas, temperature and pressure at the time of volume measurement is normalized to the so-called normal conditions. This is called Normal m3.
Beware, there are two standards and therefore the possibilities of errors in conversions:
pressure identical 1013 millibars (average atmospheric pressure) for 2 standards
DIN 1343: a temperature of 273.15K (0 ° C)
ISO 2533: a temperature of 288.15K (15 ° C)
For calculations of losses, the dimensions of the volumes of gas (compressed or not) moved into the ducts shall be given in cubic meters (m3).
For conversion of m3 or Nm3 Nm3 / h m3 / h
P 1 V 1 / T 1 = P 2 V 2 / T 2
P1 and T1 being normal temperatures and pressures v1 is the normal volume (relaxed)
P2 and T2 are the temperatures and gas pressure V2 is the volume of compressed gas
P = Absolute pressure ( pressure gauge + atmospheric pressure )
V = volume
T = temperature in Kelvin