Photoacoustic hygrometer for icing wind tunnel water content measurement: design, analysis, and intercomparison

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 high ice conditions with relevance fundamental icing research, aviation testing, certification. The single-wavelength single-pass PA absorption cell is calibrated molar vapor fractions two-pressure humidity generator integrated into instrument. Laboratory showed an estimated accuracy better than 3.3 % mole fraction range 510–12 360 ppm (5 from 250–21 200 ppm) theoretical limit detection (3σ) 3.2 ppm. examined combination basic isokinetic evaporator probe (IKP) sampling system designed wind tunnel applications, which general description condensed (CWC) measurements uncertainties are presented. Despite current limitation IKP to hydrometeor mass flux below 90 gm-2s-1, CWC 20 achieved by instrument above 0.14 g m−3 cold air (−30 ∘C) suitable background measurement. Results comparison Cranfield University drizzle rain show agreement two instruments within %, demonstrates potential hygrometers conditions.