DEVELOPMENT OF HUMIDITY MEASURING DEVICE USING POROUS CERAMIC BASED ON PRINCIPLE OF PSYCHROMETER

摘要

Hot air, both dry and moist, has been widely used for heating and/or a reaction atmosphere in a broad rangernof industrial fields including food processing, material drying, and other heat treatments. In a process thatrnuses hot air and superheated steam, the gas flow temperature, pressure, and humidity inside the treatmentrnchamber have a major impact on the quality of the finished product. However, there is no simple method ofrnmeasuring humidity that can be used over an extended duration in applications that use superheated steam atrntemperatures above 100℃. In this paper, we introduce a device developed for measuring humidity, whichrnconsists of a wetted porous ceramic probe with thermocouples, a water retention control system, andrncomputing devices. The measured humidity (steam mole fraction) is calculated from the measured wet- andrndry-bulb temperatures using the adiabatic saturation line equation on which we previously reported. Thernequation was extended to enable its application to temperatures of up to 350℃ and a humidity up to that ofrnsuperheated steam. Accuracy measurements were conducted with a humidity generator and a gas flowrntemperature of 200℃, a gas flow velocity of 3 m/s, and steam mole fraction ranging from that of hot air tornthat of superheated steam. The cause of any errors was investigated.