Measuring the dew point temperature of humid air using a photoelectric system

Abstract

Abstract

An instrument is designed and constructed to allow direct measurements to be taken of the dew point temperature of humid air. The principle uses the photoelectric system to detect the instant at which the vapour flowing over a mirror begins to condense and cloud up a mirror that is being alternately heated and cooled. A series of experimental data are extracted in different environments using this instrument. The data are in good agreement with the results obtained from analytical calculations and a psychrometric chart. The experimental data show an approximate relationship between the relative humidity and the dew point differential; i.e. for a dew point differential of 6°C below the dry bulb temperature, the relative humidity of the air is approximately 70 per cent over a moderate range of dry bulb temperatures, regardless of the barometric pressure.