Residence time distribution measurements for model flows based on laser-induced breakdown spectroscopy

A method of measuring the residence time distribution (RTD) of flow is proposed using laser-induced breakdown spectroscopy (LIBS) with an argon tracer. As a proof-of-concept study, the method is applied to measure the RTDs of two flow devices that mimic a plug flow tube and a well-stirred vessel at cold (non-reacting) conditions. Argon emission lines are first observed to avoid interference with the lines of carbon, hydrogen, oxygen, and nitrogen and their areas are calibrated to provide the argon concentration. Argon is injected to the air stream as a Heaviside (step) function, and the RTDs are obtained by differentiating the temporal changes in the argon concentration traced using LIBS. The method is expected to be used for designing reactors and validating the results of numerical studies.