Fluorescence depolarisation monitoring of liquid flow before and after exiting a slit nozzle

Abstract

Steady-state fluorescence depolarisation was used to study the hydrodynamics of ethylene glycol flow inside a quartz slit nozzle for 24 mm (Re~200) and outside as a free thin jet, for 14 mm. The polarisation profiles (over 1000 points) allowed direct evaluation of the velocity gradient within the flowing liquid from this molecular-level probe. Inside the nozzle two lateral boundary layers were observed. The velocity profile was flattened, which was attributed to strong chemical interactions with the walls of the cell. Within the jet, four polarisation profile maxima were observed for the first time, corresponding to two internal converging streams.