What is the difference between dew point and pressure dew point?
The term "pressure dew point" is used when the Dew point temperature of gases at pressures above the ambient pressure is measured. These are so the dew point temperature of a pressurized standing gas. This is of particular importance since the pressure changes, the dew point temperature of the relevant gas changes.
What influence does the pressure have on the dew point?
With increasing gas pressure also increases the Dew point temperature. The following is an example of air at ambient pressure of 1013.3 mbar and a Dewpoint temperature of -10 ° C explained.
the above table is the water vapor partial pressure (indicated by "e") 2.8 mbar. Compresses now this air, doubling the total pressure to 2,026.6 mbar, doubles according to Dalton's law also the partial pressure of water vapor (e) to a value of 5.6 mbar. This value of 5.6 mbar now corresponds to one Dew point temperature of about -1 ° C. Thus increases with the Air pressure also the dew point temperature of the air. Vice versa decrease with expansion of a compressed gas Ambient pressure the partial pressures of all gas components including that of water vapor, so that the Dew point temperature of the gas decreases. The relationship between the total pressure to the water vapor partial pressure, e, can be described as follows:
P1 / P2 = e1 / e2
After the conversion of the dew point temperature into the corresponding saturation vapor pressure let itself easily the influence of the change of the total pressure on calculate the saturation vapor pressure. The calculated Saturation vapor pressure can then return to the corresponding dew point temperature to be converted.
These calculations can be done using tables but they are also done through a series of programs. Why is knowledge about the dew point of the compressed air important?
The meaning of the dew point temperature of the compressed air depends on their respective purpose. In many cases, the question about the dew point disregarded (portable compressors for Pneumatic tools, tire pressure systems at petrol stations, etc.). In some cases, the dew point is only important because the lines, through which the air flows, temperatures below freezing are exposed, where too high a dew point can lead to freezing and blocking of the lines.
Many modern industrial plants use compressed air for operation various systems whose function in condensate formation internal parts can be affected. Some water sensitive processes using compressed air Working (eg spray painting) can be very demanding to the degree of drying. For medical and pharmaceutical processes can be steam or other Gases represent a "pollution", so very high Purity levels are required.
Which dew point temperature range is typical for compressed air?
The dew point temperatures of compressed air range from ambient down to -80 ° C, in some cases even lower. Compressor systems without air drying tend to produce compressed air that is saturated at ambient temperature. Systems with refrigeration dryers direct the compressed air through a cooled heat exchanger, so that the moisture from the air flow condenses. Such systems typically produce compressed air with a dew point not lower than +3 ° C. With
Desiccant drying systems absorb the water vapor from the air stream, reaching dew points of -40 ° C tp and below.