Molecular Tagging Velocimetry for exploring rarefied gas flows

Overview & Synopsis

Molecular tagging velocimetry (MTV) is an optical, non-intrusive measurement technique, which has been widely used for gas and liquid flow visualization. The velocity measurement is realized by recording the temporal evolution of photoluminescence emission of tracer molecules, such as acetone vapor, which follow the gas flow. In this work, MTV was used for measuring velocity fields of rarefied gas flows in a millimetric channel. However, it is necessary to couple the molecular displacement measurements to a reconstruction method based on the advection-diffusion equation, in order to correctly extract the velocity profiles of the flow. In order to successfully implement this method, a correct estimation of the diffusion coefficient of the tracer molecules is necessary. Nevertheless, there is currently no definitive agreement in the literature regarding the value of the kinetic diameter of acetone, which compromises also the estimation of the diffusion coefficient. In this thesis, the diffusion coefficient was measured by recording the temporal evolution of the widening tagged line of acetone vapor. This work also offered an indirect experimental estimation of the kinetic diameter of acetone. This measurement helped us to improve the velocimetry measurements obtained via MTV in a novel transparent channel at low pressures.