Standard Test Method for Water Vapor Content in Compressed Air Using Electronic Moisture Analyzers

Importancia y uso:

5.1 Water vapor is ubiquitous and a basic contaminant in compressed air. It cannot be eliminated but shall be controlled. Knowledge of the vapor content of compressed air is important for industrial processes to ensure that compressors that generate compressed air are functioning properly and equipment and systems that use the compressed air will function properly and maintain high reliability. This test method describes the measurement of water vapor using direct readout electronic instrumentation. Measurements are provided as dew point/frost point and calculations of related unitless quantities (ppm) are provided. Sampling techniques and warnings are provided to reduce false readings caused by contamination from the sampling method. Dry compressed air typically has a frost point between –80 °C and –40 °C (0.5 PPM_V to 127 PPM_V) at atmospheric pressure.

5.2 Measurement of moisture in compressed air can be done after regulating the pressure down to ATM or measured at elevated pressure up to the full system pressure. When measurements are made of the actual dew point (for example, condensation) or the related property of vapor pressure, the value of the dew point (and vapor pressure) is directly affected by the sample pressure since the vapor pressure is a component of the total pressure. The relationship between vapor pressure and moisture content (and dew point) is well defined below 5 MPa, but at greater pressures, additional study needs to be done to define this relationship.

5.3 Electronic moisture analyzers are also used for measuring moisture levels in other gases, including gaseous fuels. See Test Method D5454. In addition, tunable diode laser spectroscopy (TDLAS) is another technology that may be applicable to detecting moisture in compressed air. This technology is already being used in gases. See Test Method D7904.

Subcomité:

D22.13

Volúmen:

11.07

Número ICS:

71.100.20 (Gases for industrial application)

Palabras clave:

dew point; humidity; hygrometer; temperature; vapor pressure dew point;