Concentration measurements in a round hydrogen jet using Background Oriented Schlieren (BOS) technique

The current work is devoted to the development and the usability evaluation of the technique for the concentration measurements based on the Background Oriented Schlieren (BOS) method. Originally, the BOS procedure was developed for visualization and acquiring qualitative information only. In the current work it was shown that if supplementary information concerning the studied object can be accomplished, then in some cases not only qualitative but quantitative information can be obtained as well. In the case of axial symmetry of an object, the BOS method can be used for evaluation of the distribution for both concentration gradient and the concentration itself. The method was applied for the study of free expanding vertical axisymmetric hydrogen jets. In the course of the study the quasi-stationary hydrogen jet evolved from a nozzle of 21 mm internal diameter with constant mass flow rate equal to 3 g/s was examined. To validate the concentration values obtained using the proposed technique an independent set of simultaneous measurements were performed by sampling probe method. Various locations of ʹprobe capturingʹ to be measured by the gas analyzer at different locations were utilized. To obtain source images the digital single-lens reflex camera with a resolution 4368 × 2912 pixels was used. The raw images were processed with a computer program based on a PIV-type cross-correlation algorithm extended with the proposed procedure. Results of the trials demonstrated ability of the proposed technique successfully predict concentration distributions with satisfactory accuracy.