Compressed Air and Maximum 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 (kg per 100 m3) in saturated air

Mass of Water in Air (kgH2O/100 m3 free saturated air)
Pressure (bar, gauge)
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

Pressure in psi (gauge)

mass of water (lb per 100 ft3) in saturated air

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.

Related Topics

  • Air Psychrometrics - The study of moist and humid air - psychrometric charts, Mollier diagrams, air-condition temperatures and absolute and relative humidity and moisture content
  • Gases and Compressed Air - Air, LNG, LPG and other common gas properties, pipeline capacities, sizing of relief valves

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