Development of fluorescent tracers for velocimetry measurements in multiconstituent /multiphase flows

• Main Author: Chennaoui, Mourad
• Published: University of Edinburgh 2008
• Subjects: 620.106
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.642793

This thesis describes the development of optimised fluorescent dye-doped tracer droplets for gas phase particle image Velocimetry (PIV), to study mixing in multi-phase flows. The use of these tracer droplets in applications where flare can be an obstacle to obtaining velocity flow data is also demonstrated. In PIV, micron-sized tracer particles are normally required to accurately follow the flow while in the same time providing optimum fluorescence signal for proper image capture. Thus, there is a requirement to identify dyes with high quantum yield that can be dissolved in suitable nebulisable solvents at high concentrations and to investigate the effect of high concentration on fluorescence properties, such as fluorescence concentration quenching effects that could lead to a decrease of the fluorescence signal from tracer droplets. The selection criteria of candidate dyes and the study of their fluorescence properties by steady-state spectrofluorometry are presented. Bis-MSB and DCM were identified to be the optimum blue and red emitting dyes and to offer high solubility in <i>o</i>-xylene and DMSO respectively. A novel experimental approach employing stabilised emulsions to emulate the fluorescence properties of micron-sized tracer droplets has been developed. The development of a single-colour-camera PIV system that can image micron-sized and spectrally distinct fluorescent tracers in a two-phase flow is reported. The use of dye-doped microemulsions in a novel micro-PIV seeding methodology for full field velocity measurements in microfluidic devices is presented. This approach gives improved particle image contrast and reduced motion parallax uncertainty, when compared to conventional solid seed particles. Results of micro-PIV measurements in T- and Y-junction microfluidic chips are presented. Channel velocity profiles were found to agree with CFD simulations.