Development of High-Temperature Wide-Range Humidity Sensor by Wetted Material Temperature Measurement (Improvement of Measurement Accuracy by Considering the Effect of Supplied Water)

Abstract

A high-temperature wide-range humidity sensor has been developed using wetted material temperature measurement. A porous ceramic is used as a sensing element; it has a small tube for supplying water to maintain a wetted surface. However, the water supplied to the elements can affect the surface temperature. In this study, we experimentally investigate the accuracy of the developed sensor and its contributing factors-convective heat transfer, evaporation, radiant heat, and the water supplied to the wetted material-under the conditions of a gas flow temperature of 200 °C, gas flow velocity of 3 or 5 m/s, flow rate of supplied water of 0.01-0.05 g/s, and steam mole fraction of 0.03-1.00. Further, we calculate the heat flux and the surface temperature using a one-dimensional heat transfer model to clarify the effects of the each of the abovementioned factors. Consequently, we conclude that the supplied water strongly affects the accuracy of the developed sensor. We also improve the measurement error of the steam mole fraction from 0.07 to 0.03 by the controlling the flow rate of the supplied water.