Air - Altitude, Density and Specific Volume
Density and the specific volume of air vary with elevation above sea level
The density of air varies with pressure (the Ideal Gas Law) and the altitude above sea level. Mean absolute pressure at sea level is approximately 760 mmHg (101.325 kPa, kN/m2) with a variation is about +/- 5%.
The chart above can be used to estimate "temperature vs. elevation density correction factor". The density at a given temperature and elevation can then be calculated as
Altitude and Air Pressure
The air barometer pressure varies with altitude as shown in the table below:Altitude (m) | Pressure | |
---|---|---|
(mmHg) | (kPa) | |
0 | 760 | 101.3 |
75 | 753 | 100.4 |
150 | 746 | 99.5 |
250 | 739 | 98.5 |
300 | 733 | 97.7 |
450 | 719 | 95.9 |
600 | 706 | 94.1 |
750 | 693 | 92.4 |
900 | 681 | 90.8 |
1000 | 668 | 89.1 |
1200 | 656 | 87.5 |
1350 | 644 | 85.9 |
1500 | 632 | 84.3 |
1800 | 609 | 81.2 |
2100 | 586 | 78.1 |
2400 | 564 | 75.2 |
Altitude and Air Density
Air density and specific volume as functions of altitude above sea level can be indicated as in the diagrams below:STP - Standard Temperature and Pressure
- STP - Standard Temperature and Pressure is 0oC and 101.325 kN/m2.
NTP - Normal Temperature and Pressure
- NTP - Normal Temperature and Pressure, commonly used for testing and documentation of fan capacities, is 20oC and 101.6 kN/m2 (68oF, 30 in Hg)
Altitude and Specific Volume Correction
The specific volume of standard air at a certain altitude can be calculated by multiplying with the volume correction factor belowAltitude | Volume Correction Factor | |
---|---|---|
(m) | (ft) | |
0 | 0 | 1.00 |
480 | 1600 | 1.05 |
990 | 3300 | 1.11 |
1500 | 5000 | 1.17 |
1980 | 6600 | 1.24 |
2460 | 8200 | 1.31 |
2970 | 9900 | 1.39 |
Altitude and Air Pressure
Altitude | Pressure | ||||
---|---|---|---|---|---|
feet | meter | inHg | torr | psia | kPa |
0 | 0 | 29.92 | 759.97 | 14.7 | 101.3 |
500 | 152 | 29.39 | 746.51 | 14.43 | 99.4 |
1000 | 305 | 28.86 | 733.04 | 14.17 | 97.6 |
1500 | 457 | 28.34 | 719.84 | 13.91 | 95.8 |
2000 | 610 | 27.82 | 706.63 | 13.66 | 94.1 |
2500 | 762 | 27.32 | 693.93 | 13.41 | 92.4 |
3000 | 914 | 26.82 | 681.23 | 13.17 | 90.7 |
3500 | 1067 | 26.33 | 668.78 | 12.93 | 89.1 |
4000 | 1219 | 25.84 | 656.34 | 12.69 | 87.4 |
4500 | 1372 | 25.37 | 644.4 | 12.46 | 85.8 |
5000 | 1524 | 24.9 | 632.46 | 12.23 | 84.3 |
5500 | 1676 | 24.44 | 620.78 | 12 | 82.7 |
6000 | 1829 | 23.98 | 609.09 | 11.77 | 81.1 |
6500 | 1981 | 23.53 | 597.66 | 11.55 | 79.6 |
7000 | 2134 | 23.09 | 586.49 | 11.34 | 78.1 |
7500 | 2286 | 22.66 | 575.56 | 11.13 | 76.7 |
8000 | 2438 | 22.23 | 564.64 | 10.91 | 75.2 |
8500 | 2591 | 21.81 | 553.97 | 10.71 | 73.8 |
9000 | 2743 | 21.39 | 543.31 | 10.5 | 72.3 |
9500 | 2896 | 20.98 | 532.89 | 10.3 | 71.0 |
10000 | 3048 | 20.58 | 522.73 | 10.1 | 69.6 |
10500 | 3200 | 20.19 | 512.83 | 9.91 | 68.3 |
11000 | 3353 | 19.8 | 502.92 | 9.72 | 67.0 |
11500 | 3505 | 19.41 | 493.01 | 9.53 | 65.7 |
12000 | 3658 | 19.03 | 483.36 | 9.34 | 64.4 |
12500 | 3810 | 18.66 | 473.96 | 9.16 | 63.1 |
13000 | 3962 | 18.3 | 464.82 | 8.99 | 61.9 |
13500 | 4115 | 17.94 | 455.68 | 8.81 | 60.7 |
14000 | 4267 | 17.58 | 446.53 | 8.63 | 59.5 |
14500 | 4420 | 17.24 | 437.9 | 8.46 | 58.3 |
15000 | 4572 | 16.89 | 429.01 | 8.29 | 57.1 |
15500 | 4724 | 16.56 | 420.62 | 8.13 | 56.0 |
16000 | 4877 | 16.22 | 411.99 | 7.96 | 54.8 |
16500 | 5029 | 15.9 | 403.86 | 7.81 | 53.8 |
17000 | 5182 | 15.58 | 395.73 | 7.65 | 52.7 |
17500 | 5334 | 15.26 | 387.6 | 7.47 | 51.5 |
18000 | 5486 | 14.95 | 379.73 | 7.34 | 50.6 |
18500 | 5639 | 14.65 | 372.11 | 7.19 | 49.5 |
19000 | 5791 | 14.35 | 364.49 | 7.05 | 48.6 |
19500 | 5944 | 14.05 | 356.87 | 6.9 | 47.5 |
20000 | 6096 | 13.76 | 349.5 | 6.76 | 46.6 |
20500 | 6248 | 13.48 | 342.39 | 6.62 | 45.6 |
21000 | 6401 | 13.2 | 335.28 | 6.48 | 44.6 |
21500 | 6553 | 12.92 | 328.17 | 6.34 | 43.7 |
22000 | 6706 | 12.65 | 321.31 | 6.21 | 42.8 |
22500 | 6858 | 12.38 | 314.45 | 6.08 | 41.9 |
23000 | 7010 | 12.12 | 307.85 | 5.95 | 41.0 |
23500 | 7163 | 11.86 | 301.24 | 5.82 | 40.1 |
24000 | 7315 | 11.61 | 294.89 | 5.7 | 39.3 |
24500 | 7468 | 11.36 | 288.54 | 5.58 | 38.4 |
25000 | 7620 | 11.12 | 282.45 | 5.46 | 37.6 |
25500 | 7772 | 10.88 | 276.35 | 5.34 | 36.8 |
26000 | 7925 | 10.64 | 270.26 | 5.22 | 36.0 |
26500 | 8077 | 10.41 | 264.41 | 5.11 | 35.2 |
27000 | 8230 | 10.18 | 258.57 | 5 | 34.5 |
27500 | 8382 | 9.96 | 252.98 | 4.89 | 33.7 |
28000 | 8534 | 9.74 | 247.4 | 4.78 | 32.9 |
28500 | 8687 | 9.53 | 242.06 | 4.68 | 32.2 |
29000 | 8839 | 9.31 | 236.47 | 4.57 | 31.5 |
29500 | 8992 | 9.11 | 231.39 | 4.47 | 30.8 |
30000 | 9144 | 8.9 | 226.06 | 4.37 | 30.1 |
Temperature vs. Elevation Density Correction
The chart above can be used to estimate "temperature vs. elevation density correction factor". The density at a given temperature and elevation can then be calculated as
ρ = ρref / f (1)
where
ρ = density at the given temperature and elevation (lbm/ft3)
ρref = density reference at elevation 0 ft and temperature 70 oF - (0.075 lbm/ft3)
f = correction factor from the chart above
Example - Density at Elevation 4000 ft and Temperature 300 oF
From the chart above - at elevation 4000 ft and temperature 300 oF the correction factor is approximate 1.7. The density can be calculated as
ρ = (0.075 lbm/ft3) / 1.7
= 0.043 lbm/ft3
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