Characterisation of liquid film in a microstructured falling film reactor using laser scanning confocal microscopy

Reflection confocal microscopy was used to measure the thicknesses of falling thin films generated using microstructured plates. Each plate contained straight parallel channels through which liquid fell vertically under gravity. Three different channel dimensions were used: 300 × 100 μm, 600 × 200 μm and 1200 × 400 μm (width × depth). Measurements were performed for acetone, ethanol and isopropanol and gave reasonable agreement with theoretical predictions and correlations from the literature. Discrepancies were attributed to the fact that these equations do not consider parameters that affect three-phase contact lines such as surface tension and contact angle. No trend of film thickness on channel width was observed and was probably due to different surface heterogeneity and roughness characteristics amongst the plates. Measurement difficulties were encountered at low liquid film thicknesses and where the angle of the liquid meniscus was too steep.