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 Fig. 5.3: A wet sponge being squeezed | Air contains water in the form of moisture. Since air can be compressed and water can not, when air is compressed the water precipitates in the form of condensate. The maximum humidity of the air depends on temperature and volume. It does not depend on quantity.
Atmospheric air can be imagined as a moist sponge. It can take in a certain amount of water when it is relaxed. But if it is squeezed, part of the water runs out. Some of the water will always stay in the sponge regardless of how hard it is squeezed. Compressed air is very similar.
The following examples illustrate the quantity of condensate to be expected q c when air is compressed. The example assumes a humid Summer day with 35° C and 80 % atmospheric humidity. |
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V1 = 6,50 m³, V2 = 0,59 m³
p1 = 0 barop = 1 barabs, p2 = 10 barop = 11 barabs
T = 35 °C
j1 = 80 %, j2 = 100 %
humax = 39,286 g/m³
Fig. 5.4: Precipitation of condensate during compression |
mK = precipitated condensate [g]
V1 = Volume at 0 bar op [m³]
V2 = Volume at 10 bar op [m³]
humax 1 = max. humidity at 35° C [g/m³]
j1 = relative humidity of V1 [%]
j2 = relative humidity of V2 [%]
Because the water that comes out of the compressed air is the part the air can not store, the humidity j of the compressed air rises to 100 %.
When compressing 6,5 m³ air to 10 bar pressure, at a constant temperature 181,108 g water will precipitate in the form of condensate. |