78 巻 (2012) 790 号 p. 1267-1278
Superheated steam-containing hot air under atmospheric pressure has been used as a heating media for thermal processing such as food processing, cooking, sterilization, drying, and waste treatment. For these types of thermal processing, the steam mole fraction of the media sometimes strongly influences product quality. Hence, a simple method is required for measuring the steam mole fraction under a high temperature of more than 250°C. In this report, we propose an equation to calculate the steam mole fraction using the adiabatic saturation temperature for a wide range of temperatures and humidity values, i.e., from room temperature to 350°C and from room air to pure superheated steam. We also present a psychrometric chart with the steam mole fraction on the y-axis, which can indicate the presence of dry air and pure superheated steam. The values calculated by the proposed equation were in good agreement with values obtained in previous literature under comparable conditions. For developing a simple and convenient measurement method, a wet spherical gauze/brick is used for measuring the wet-bulb temperature. Its accuracy and applicability are investigated experimentally. The results show that this method can measure the steam mole fraction with an accuracy of less than 0.09 in the temperature range of 160-280°C. The causes of error and the methods for intending utilization are also investigated.