No abstract

This paper outlines the development of an apparatus to supply air with both controlled temperature and relative humidity, at a variety of flow rates up to 114 L min−1. To achieve adjustable constant relative humidities in the air, the two‐pressure principle was used. This method involved saturating the air at a higher pressure, and then passing the air through a pressure release valve to the lower working pressure to achieve the desired humidity, while controlling the temperature to the desired level. The absolute pressure when the saturation is achieved determines the humidity of the final air. Standard design procedures were followed to ensure the air approached saturation in the pressurized column and that the amount of water was sufficient to make sure the columns would not run out of water during an experiment. The problems encountered included a pressure fluctuation coming from the compressor through the pressure regulator, and a regular fluctuation in the temperature of the water, within a 90 min period, when the water temperature was used to control the air temperature exiting the column. These problems were overcome by using two‐pressure regulators on the air supply and by controlling the temperature of the water rather than the air temperature. The result was a stable but adjustable temperature and relative humidity air supply.