Analysis of tracer particle characteristics for micro PIV in wall-bounded gas flows

The investigation of the gas flow in a working fuel cell by means of optical measurement techniques like micro Particle-Image Velocimetry (µPIV) requires the generation of suitable tracer particles. In this work the analysis of tracer particle characteristics is described which serves as a means to identify suitable particles for wall-bounded gas flows. Several materials and different types of particle generators were examined to check for obtainable particle size distributions and particle concentrations. a simple experiment was designed to investigate the capability of the generated particles to adequately follow the flow. an optically transparent micro-channel with a 90° elbow was manufactured and the µPIV measurement technique is applied. Firstly, the gas-flow seeded with tracer particles is investigated within this 90° elbow micro-channel. Secondly, to check whether the measured flow structure in this previous case matches with the real flow, the same flow conditions are investigated using water as working fluid with solid tracer particles taking into account Reynolds number similarity. Thirdly, cFD-calculations using the same reference parameters as in the expe- rimental investigations were performed to quantify the deviation of the particle traces from the real flow streamlines. The results show ethylene glycol to be a suitable tracer material since the obtained tracer particles are optically detectable without severe image post-processing and since this material can be easily transformed into an aerosol with suitable concentrations and particle size distributions. The application of the µPIV technique on such a gaseous particle laden flow provided promising results concerning the intended application of this technique to operating fuel cells.