Compressed air used in industrial fields needs to undergo cleaning and drying treatment. After air is compressed by air compressor, condensate water will be produced. Untreated compressed air containing condensate water can lead to:
■ Corrosion failure of pneumatic equipment;
■ The quality of air-assisted processes deteriorates;
■ The quality of the final product declines;
■ Rusting and corrosion of the pipeline led to leakage;
Therefore, the dryer is crucial for protecting the user's production system and process flow.
# Theoretical Basis and Moisture Content Standards #
How much moisture can be contained in the air? Why does condensation occur?
Air is a mixture. Besides gaseous components such as nitrogen and oxygen, it also contains solid particles like dust, sand and smoke, as well as water vapor. Air containing water vapor is called moist air.
The content of water vapor in the air is high at high temperatures and low at low temperatures.
| Atmospheric Dew Point/Moisture Content Relationship Table |
|
Dew point ℃
|
Moisture content
g/m³
|
Dew point ℃ |
Moisture content
g/m³
|
Dew point ℃ |
Moisture content
g/m³
|
Dew point ℃ |
Moisture content
g/m³
|
| 14 |
12.070 |
-5 |
3.4070 |
-24 |
0.7678 |
-43 |
0.1298 |
| 13 |
11.350 |
-6 |
3.1690 |
-25 |
0.7074 |
-44 |
0.1172 |
| 12 |
10.660 |
-7 |
2.9460 |
-26 |
0.6463 |
-45 |
0.1055 |
| 11 |
10.010 |
-8 |
2.7370 |
-27 |
0.5922 |
-46 |
0.0950 |
| 10 |
9.309 |
-9 |
2.5410 |
-28 |
0.5422 |
-47 |
0.0854 |
| 9 |
8.819 |
-10 |
2.3580 |
-29 |
0.4960 |
-48 |
0.0768 |
| 8 |
8.270 |
-11 |
2.1860 |
-30 |
0.4534 |
-49 |
0.0689 |
| 7 |
7.50 |
-12 |
2.0060 |
-31 |
0.4141 |
-50 |
0.0617 |
| 6 |
7.260 |
-13 |
1.8760 |
-32 |
0.3779 |
-51.1 |
0.0540 |
| 5 |
6.797 |
-14 |
1.7360 |
-33 |
0.3445 |
-53.9 |
0.0400 |
| 4 |
6.360 |
-15 |
1.6050 |
-34 |
0.3138 |
-56.7 |
0.0290 |
| 3 |
5.947 |
-16 |
1.4830 |
-35 |
0.2856 |
-59.4 |
0.0210 |
| 2 |
5.559 |
-17 |
1.3690 |
-36 |
0.2597 |
-62.2 |
0.0140 |
| 1 |
5.192 |
-18 |
1.2610 |
-37 |
0.2359 |
-65 |
0.0110 |
| 0 |
4.847 |
-19 |
1.1650 |
-38 |
0.2141 |
-67.8 |
0.0080 |
| -1 |
4.523 |
-20 |
1.0740 |
-39 |
0.1940 |
-70.6 |
0.0050 |
| -2 |
4.217 |
-21 |
0.9884 |
-40 |
0.1757 |
-73.3 |
0.0030 |
| -3 |
3.930 |
-22 |
0.9093 |
-41 |
0.1590 |
|
|
| -4 |
3.660 |
-23 |
0.8359 |
-42 |
0.1438 |
|
|
Relative humidity (RH) and pressure dew point (PDP) are indicators and concepts for measuring the dryness of compressed air.
The lower the relative humidity (RH) of compressed air is, the less water vapor it contains and the drier the compressed air will be. Therefore, the lower the relative humidity (RH) of compressed air is, the better.
The water vapor content in the air usually does not reach the saturated state of the maximum water content. The percentage of the actual content below the saturated state to the maximum content is the relative humidity (RH). Given the dew point and relative humidity, the water vapor content at that temperature condition can be calculated, for example:
The saturation content at the dew point (DP) of 25℃ is 22.830g/m³, and the relative humidity (RH) is 70%. Then, the content at 1m³ is 1 x 22.83 x 70% = 15.981g.
The saturation content at the dew point (DP) of 35℃ is 39.286g/m³, and the relative humidity (RH) is 100%. Then, the content at 1m³ is 1 x 39.286 x 100%=39.286g.
The standard for measuring the moisture content of compressed air is ISO8573-1:2010, which stipulates six grades of the pressure dew point (PDP) of compressed air ranging from -70℃ to 10℃. The lower the PDP number, the higher the quality requirement of the compressed air and the drier the compressed air.
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