No abstract

Water films and droplets on surfaces are important in the design of various processes. In the present work, two complementary non-invasive imaging techniques, laser-induced fluorescence (LIF) and near-infrared absorption (NIRA), were used simultaneously to quantify the deposited water mass in a simple spray-onto-plate experiment. LIF was applied in epiillumination with optical access from only one direction, but it requires the addition of a marker substance to the non-fluorescing water. Here, anisole (methoxybenzene) was used for this purpose. The present implementation of NIRA is based on the intensity ratio of light transmitted through the sample at two wavelengths, 1450 and 600 nm. Since water itself is the IR absorber, a tracer is not required. In a first step, in a thin-film cuvette the influence of temperature and film thickness on the measurement accuracy was investigated for both techniques. In a second set of experiments, water was sprayed onto a hot or cold quartz glass plate and simultaneously imaged with both techniques. From the measurements, advantages and weaknesses of both approaches were identified.