An absorption-based sensor system for accurate in situ examination of liquid film formation upon spray–wall interaction at elevated temperatures

Abstract

Thin liquid films critically influence the performance of a wide range of processes. In situ examination of these types of films is currently hindered by the limitations of available non-intrusive measurement techniques, particularly with respect to robustness and working distance. Differential absorption enables non-intrusive measurements of various film parameters in simplified laboratory configurations, but has rarely been applied under realistic process conditions due to signal contamination by spurious reflections at the film interface that severely perturb measurements. Their influence is particularly pronounced when the wetted surface is rough, as is the case for many technical surfaces. To overcome this susceptibility and enable accurate measurements, an imaging-based measurement system is proposed that allows reflections at the film interface to be identified and filtered from the signal. The concept is validated using Monte Carlo simulations and demonstrated experimentally by using it to characterize a film that forms when water is injected into a flow bench designed to facilitate experiments in the context of selective catalytic reduction (SCR). In contrast to the established sensor concept that utilizes an area-integrating detector, the newly developed system provides meaningful estimates for film temperature and thickness.