Pressure dew point: after the wet air is compressed, the density of water vapor increases and the temperature also rises. When the compressed air cools down, the relative humidity will increase. When the temperature continues to drop to 100%, water drops will come out from the compressed air, the temperature at this time is the "pressure dew point" of compressed air ".
The relationship between pressure dew point and normal pressure dew point
The corresponding relationship between the pressure dew point and the normal pressure dew point is related to the "compression ratio", which is generally expressed by charts. Under the condition of the same "pressure dew point", the higher the "compression ratio" is, the lower the normal pressure dew point it corresponds to IS. For example: when the compressed air pressure dew point of O.7MPa is 2℃, the normal pressure dew point is-23℃. When the pressure increases to 1.0MPa and the dew point of the same pressure is 2℃, the corresponding normal pressure dew point drops to-28℃
Pressure dew point measurement
Although the unit of pressure dew point is ℃, its connotation is the water content of compressed air. Therefore, measuring the dew point is actually measuring the moisture content of the air. There are many instruments for measuring compressed air dew point, such as mirror dew point meter, electric sensor Dew Point meter, dielectric method Dew Point meter, Crystal oscillating Dew Point meter, infrared Dew Point meter, semiconductor sensor Dew Point meter, such as MICHELL Dew Point meter in Britain, the measuring range of this instrument can reach-100℃.
Precautions for measuring pressure dew point
Use the dew point meter to measure the air dew point, especially when the water content of the tested air is very low, the operation should be very careful and patient. The gas sampling equipment and connecting lines must be dry (at least more dry than the tested gas), the connection of lines should be completely sealed, and the gas flow rate should be selected according to the regulations, moreover, a long enough pretreatment time is required. A little carelessness will lead to a large error. It is proved that there is a big error when measuring the "pressure dew point" of the compressed air processed by the cold dryer by using the "micro-moisture analyzer" using phosphorus pentoxide as electrolyte. According to the manufacturer's explanation, this is because the compressed air will produce "secondary electrolysis" during the test process, which makes the read value higher than the actual value.
