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 | 0.45 | 0.15 | 0.091 | 0.065 | 0.051 |
| 20 | 1.8 | 0.58 | 0.35 | 0.25 | 0.19 |
| 40 | 5.9 | 1.9 | 1.1 | 0.79 | 0.62 |
| 60 | 18 | 5.3 | 3.1 | 2.2 | 1.7 |
| 80 | 65 | 14 | 7.8 | 5.4 | 4.1 |
| 100 | 38 | 19 | 13 | 9.4 | |
| 120 | 49 | 29 | 21 | ||
- 1 kg/m3 = 0.0624 lb/ft3
Pressure in psi (gauge)
Example - Water Extracted from an Air Compressor
Free air enters a compressor at atmospheric conditions 20oC and 70% humidity ratio. The air leaves saturated at gauge pressure 8 bar and 40oC.
Based on the diagram and table above the water content in saturated air entering the compressor can be estimated to be approximately 1.8 10-2 kg per m3 free air (0.018 kgwater/m3air).
The amount of water with 70% saturation can be calculated as
(0.018 kgwater/m3air) (70%) / (100%)
= 0.0126 kgwater/m3air
The water content in the 100% saturated air leaving the compressor can be estimated from above to be approximately 0.62 10-2 kg per m3 free air (0.0062 kgwater/m3air).
The water extracted in the compressor can be calculated as
(0.0126 kgwater/m3air) - (0.0062 kgwater/m3air)
= 0.0064 kgwater/m3air
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