Experimental setup at the X-ray beamline and comparison with simulations. (a) Schematic of mixer placed at a 35° angle to the incident X-rays. (b) Mixer mounted on the beamline plate during X-ray operation. (c) Line-of-sight integrated profile of predicted axisymmetric concentration fields for all Fe species (top row) and measured Fe X-ray fluorescence (bottom row). The gray area in the X-ray image depicts the region where the sample stream cross-sectional area is too small for X-ray detection. Note that the convolutive effect of the X-ray beam significantly widens the apparent sample. (d) The left ordinate (corresponding to the line) is the predicted sample FWHM wsa and the right ordinate (corresponding to the symbols) is the sample width associated with the emitted X-ray intensities wx. Both quantities are plotted versus the axial position x and data are for the same flow conditions as (c). The vertical and horizontal uncertainty bars, respectively, correspond to the standard deviation of wx among four different methods of measuring the emitted X-ray intensity and the X-ray beam FWHM along x. The inset shows the experimental device and a zoomed-in view of an example X-ray mark on the polyimide capillary.