Dual-wavelength absorption technique for dryness measurement of wet steam

Abstract

This paper presents a dual-wavelength absorption-based approach for measuring and validating the steam dryness fraction of wet steam. A thermally insulated steam cell with a temperature-controlled measurement window (up to 200°C) is designed and fabricated to minimize condensation during water vapor measurements at different operating pressures (1–10 bars). Water vapor’s measurement sensitivity and accuracy are limited due to other absorbing and non-absorbing species in wet steam. The measurement accuracy is significantly improved with the proposed dual-wavelength absorption technique (DWAT) measurement method. The influence of modifying factors—namely, pressure and temperature—on water vapor absorbance is minimized by a non-dimensional correction factor. The dryness is measured with the help of the water vapor concentration and wet steam mass present in the steam cell. The DWAT dryness measurement approach is validated using a four-stage separating and throttling calorimeter combined with a condensation rig. The accuracy of the dryness measurement system using this optical method is determined to be ±1% for the range of dryness and operating pressure (1–10 bars) of wet steam.