1. Photoacoustic hygrometer for icing wind tunnel water content measurement: Design, analysis and intercomparison
- Author
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Hugo Pervier, Philipp Breitegger, Benjamin Lang, Alexander Bergmann, Wolfgang Breitfuss, Andreas Tramposch, Wolfgang Hassler, Simon Schweighart, and Andreas Klug
- Subjects
020301 aerospace & aeronautics ,Atmospheric Science ,010504 meteorology & atmospheric sciences ,Hygrometer ,lcsh:TA715-787 ,near-infrared laser diode-based photoacoustic (PA) hygrometer ,lcsh:Earthwork. Foundations ,Freezing drizzle ,Humidity ,02 engineering and technology ,01 natural sciences ,Atmospheric icing ,lcsh:Environmental engineering ,0203 mechanical engineering ,Calibration ,Environmental science ,lcsh:TA170-171 ,Water content ,Water vapor ,0105 earth and related environmental sciences ,Icing ,Remote sensing - Abstract
This work describes the latest design, calibration and application of a near-infrared laser diode-based photoacoustic (PA) hygrometer developed for total water content measurement in simulated atmospheric freezing precipitation and high ice water content conditions with relevance in fundamental icing research, aviation testing, and certification. The single-wavelength and single-pass PA absorption cell is calibrated for molar water vapor fractions with a two-pressure humidity generator integrated into the instrument. Laboratory calibration showed an estimated measurement accuracy better than 3.3 % in the water vapor mole fraction range of 510–12 360 ppm (5 % from 250–21 200 ppm) with a theoretical limit of detection (3σ) of 3.2 ppm. The hygrometer is examined in combination with a basic isokinetic evaporator probe (IKP) and sampling system designed for icing wind tunnel applications, for which a general description of total condensed water content (CWC) measurements and uncertainties are presented. Despite the current limitation of the IKP to a hydrometeor mass flux below 90 gm-2s-1, a CWC measurement accuracy better than 20 % is achieved by the instrument above a CWC of 0.14 g m−3 in cold air (−30 ∘C) with suitable background humidity measurement. Results of a comparison to the Cranfield University IKP instrument in freezing drizzle and rain show a CWC agreement of the two instruments within 20 %, which demonstrates the potential of PA hygrometers for water content measurement in atmospheric icing conditions.
- Published
- 2020