Fluids Constants

This is a technical reference post that simply lists all the physical constants used in fluid calculations.

 

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.

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