Ventilation Grille Sizing

The aspect ratio is

Length
______   of the grille.
Breadth

(Total volume flow rate [m³ . s^-1]).(100)
______________________________________________= Area (m²)
(No. inlets).( inlet velocity [m . s^-1]).( per cent free area)

Fluids Constants

SPECIFIC HEAT CAPACITY OF DRY AIR
1.01 . kJ . kg^-1 . C^-1 da

SPECIFIC HEAT CAPACITY OF WATER VAPOUR
1.89 . kJ. kg^-1

SPECIFIC HEAT CAPACITY OF ATMOSPHERIC AIR (stp)
1.012 . kJ . kg^-1 . C^-1

MEAN SPECIFIC HEAT CAPACITY OF WATER
4.185 . kJ. kg^-1

LATENT HEAT OF WATER VAPOUR AT 273K (0C)
2500 . kW

SPECIFIC MASS OF WATER (stp)
1000 . kg . m^-3

SPECIFIC MASS OF ATMOSPHERIC AIR AT 293K (20C)
1.205 . kg . m^-3

VELOCITY OF SOUND IN AIR
330 . m . s^-1

ATMOSPHERIC PRESSURE

The standard atmosphere (1.atm) =

101 325 Pa  — or 101.325 kPa.

The following units are equivalent, but only to the number of decimal places shown:

• 760 mm Hg (Torr),
• 29.92 in Hg,
• 14.696 PSI,
• 1013.25 millibars.

One standard atmosphere is standard pressure used for pneumatic fluid power (ISO R554), and in the aerospace industry(ISO 2533) and petroleum industry(ISO 5024) .

Temperature Correcting

Because the specific mass of atmospheric air at 293 . K

= [1.205 . (293. K/293 . K) ] . kg . m^-3

= 1.205 . kg . m^-3

So the specific mass of atmospheric air at a temperature of 29.C

= [1.205 . (293 /273+29) ] . kg . m^-3

= [1.205 . (293 /302) ] . kg . m^-3

= 1.169 . kg . m^-3

which is the specific mass corrected for the higher temperature.

Composition of Air

COMPOSITION		% by volume
N2	Nitrogen	78.03
O2	Oxygen	20.99
A	Argon	0.94
CO2	Carbon dioxide	0.03
H2	Hydrogen	0.01
others		parts per million
Ne	Neon	0.001230
He	Helium	0.000400
Kr	Krypton	0.000050
Xe	Xenon	0.000006