Compressed Air and Water Content
Saturation pressure and maximum water content in compressed air
The maximum content of water in air at saturated conditions decrease with pressure and increase with temperature as indicated in the diagrams below.
Pressure in bar (gauge)
| Mass of Water in Air (10-2 kgH2O/m3 free saturated air) | |||||
|---|---|---|---|---|---|
| Temperature (oC) | Pressure (bar gauge) | ||||
| 0 | 2 | 4 | 6 | 8 | |
| 0 | 0.48 | 0.17 | 0.10 | 0.07 | 0.05 |
| 20 | 1.7 | 0.58 | 0.35 | 0.25 | 0.19 |
| 40 | 5.1 | 1.7 | 1.0 | 0.73 | 0.57 |
| 60 | 13 | 4.3 | 2.6 | 1.9 | 1.4 |
| 80 | 29 | 9.7 | 5.8 | 4.2 | 3.2 |
| 100 | 56 | 19 | 12 | 8.4 | 6.5 |
| 120 | 37 | 22 | 16 | 12 | |
- 1 kg/m3 = 0.0624 lb/ft3
Pressure in psi (gauge)
Example - Water Extracted from an Air Compressor
100 m3 of free air enters a compressor at atmospheric conditions 20oC and 70% water content. The air leaves saturated at gauge pressure 8 bar and 40oC.
Based on the diagram and table above the water content in the entering air can be estimated to approximately 1.7 kg per 100 m3 free air. 70% of this is 1.19 kg per 100 m3.
The water content in the air leaving the compressor can be estimated to approximately 0.57 kg per 100 m3 free air since the air is saturated - holding 100% of maximum water capacity.
The difference
(1.19 kg) - (0.57 kg) per 100 m3 free air
= 0.62 kg per 100 m3 free air
is extracted in the compressor.
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