Water-film thickness imaging based on time-multiplexed near-infrared absorption with up to 500  Hz repetition rate

Abstract

We demonstrate high-repetition-rate imaging of the liquid-film thickness in the 50–1000 µm range resulting from impinging water droplets on a glass surface. The pixel-by-pixel ratio of line-of-sight absorption at two time-multiplexed near-infrared wavelengths at 1440 and 1353 nm was detected with a high-frame-rate InGaAs focal-plane array camera. Frame rates of 1 kHz and thus measurement rates of 500 Hz could be achieved, well suited to capture the fast dynamics of droplet impingement and film formation. The droplets were sprayed onto the glass surface using an atomizer. Suitable absorption wavelength bands for water droplet/film imaging were determined from Fourier-transform infrared (FTIR) spectra of pure water between 298 and 338 K. At 1440 nm, the water absorption is nearly temperature-independent, making the measurements robust against temperature fluctuations. Time-resolved imaging measurements capturing the dynamics of the water droplet impingement and evolution were successfully demonstrated.

Numerical study on the three-dimensional flow of water film on the outer surface of the hollow stationary blade

“…The water film flow thickness was calculated based on the deposition of the droplet and an empirical model of water film flow. Lubnow et al 24 developed a water film imaging method based on time-multiplexed near-infrared absorption with up to 500 Hz repetition rate. The water film thickness in the range of 50–1000 μm has been tested.…”