Development of High-Temperature Wide-Range Humidity Sensor by Wetted Material Temperature Measurement (Application of Porous Ceramic into Sensing Element)

Abstract

We applied the theory of a psychrometer to develop a humidity monitoring system by using cylindrical porous ceramic as a sensing element. This system contains a section for supplying/discharging water. Several types of porous ceramics were made and the effects of porosities and pore size distributions on capillary water transfer were investigated. Also, we tested the performance of this system in terms of its response time and measurement accuracy. The capillary water transfer was higher in the conditions that porosity was larger and pore size distribution was wider. In addition, at a gas flow rate of 1 m/s and a gas temperature less than 310 °C, the error of the steam mole fraction was observed to be less than 10 %. Further, the system had a 90 % response time of less than 60 s and this time was shorter as humidity increased at a gas temperature of 200 °C, a gas flow of 1 m/s, a flow rate of supplied water of 0.01 g/s and a water temperature of 25 °C when a sensing element diameter was 9 mm.