By this, the air temperature T drops under the dew point temperature of Td = 10☌ (50☏), which causes condensation in the pipe. In a secondary pipeline, the same air is cooled to T = 5☌ (41☏) by cold weather. The RH is now = 28.9%, and consequently there no risk of condensation. The air is then dried to a dew point of Td = 10☌ (50☏) and thereby cooled to 30☌ (86☏). Thus, the air has a dew point temperature Td = 50☌ (122☏) and the relative humidity RH = 100%. The air at the compressor outlet is at 50☌ (122☏) and is fully saturated. Here's a practical example of this relationship in a compressed air network: These relationships, including the calculation of measurement uncertainties, can be calculated very easily with an online calculator, such as the E+E Elektronik’s humidity calculator. When the air temperature approaches the dew point temperature, the relative humidity increases and, with it, the risk of condensation. As of this point, the air cannot hold any more water vapor, resulting in condensation.Īs the dew point temperature relates to the absolute amount of water vapor in the air, it is not affected by changes of the air temperature. The maximum possible water vapor partial pressure in the air is called saturation vapor pressure and is determined by the temperature. PTotal = pN 2 + pO 2 + pAr + pCO 2 + e‘ or pTotal = pa + e‘ For the total pressure of humid air, the following applies: Therefore, for fully dry air at sea level (1013.25 hPa) the following applies:Īnother common component of air is water vapor (= water in its gaseous phase). Other components of air can be ignored as their share is negligible. The main constituents of air are nitrogen (N 2), oxygen (O 2), argon (Ar) and carbon dioxide (CO 2). In contrast, the measurement of relative humidity (RH) indicates how close the air is to the saturation point.ĭalton's Law states the total pressure of an (ideal) gas mixture is the sum of the partial pressures of the individual gases. The dew point measurement relates to the absolute amount of water vapor contained in the air. The dew point, or dew point temperature (Td), is the temperature to which the air must be cooled for the water contained in the air to start condensing. Reliable measurement and continuous monitoring of the dew point in compressed air systems using dew point transmitters, such as the E+E Elektronik EE371, can help ensure smooth production processes and product quality. The following explains the basics of dew point measurement and what is important in practice. Therefore, operators of compressed air systems should address this issue before it causes serious and costly issues. A too high humidity content can have negative effects on the quality of the final product, lead to problems during the manufacturing process, or even result in complete system shutdown. The dew point provides information about the absolute humidity content of the compressed air. Wherever compressed air is used, accurate and continuous monitoring of the dew point temperature is advisable.
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