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A Humidity Generator for Temperatures to 200 °C and Pressures to 1.6 MPa



D Vega-Maza, W Wyatt Miller, Dean C. Ripple, Gregory E. Scace


We have constructed a new humidity generator that produces gas streams of known moisture content at temperatures from 85 °C to 200 °C, absolute pressures from 0.2 MPa to 1.6 MPa, and relative humidities from 10 % to 90 %. The generator produces a moist gas stream by injecting fixed-rate streams of dry gas and liquid water into a vaporizer, where the water evaporates into the gas. The gas stream passes into a re-entrant RF cavity, which serves as our reference hygrometer, and then a test chamber. The present standard uncertainty of the RF hygrometer is 0.6 %, limited by uncertainty of literature values for the polarizability of water. Dry nitrogen gas purging the pressure transducer line also combines with the moist gas stream downstream of the test chamber and flows through one of a set of capillaries. Modulation of gas flow through the fixed flow impedance of the capillary gives a simple method for controlling pressure. Individual insulated, temperature-controlled aluminum ovens enclose each major component. A larger oven encloses these ovens and connecting tubing. To minimize corrosion, critical components are constructed of high-nickel alloys. The small total volume (
International Journal of Thermophysics


fuel cell, humidity, humidity generator, steam, water
Created November 30, 2012, Updated November 10, 2018