Characterizing the mixing effectiveness of systems or processes in granular applications is difficult due to ineffective sampling procedures and a lack of quantifiable measurement techniques. The mixing effectiveness of a screw pyrolyzer consisting of a binary mixture of 500–6350 μm red oak chips and 300–500 μm glass beads is evaluated using optical visualization and composition analysis techniques. The mass fraction of binary mixture samples is determined and the weighted sample variance from four outlet ports is used to evaluate the mixing effectiveness. The effect of dimensionless screw pitch on the mixing effectiveness is investigated at levels of p/D = 0.75, 1.25, and 1.75. Optical visualization is captured across the entire mixing region’s periphery allowing qualitative observations to be made, leading to the visual observation that increasing the dimensionless screw pitch increases the mixing effectiveness. Quantitative composition analysis utilizing a one-way analysis of variance (ANOVA) statistical model confirms that increasing the dimensionless screw pitch from 0.75 to 1.25 results in a significant increase in mixing effectiveness. However, diminishing increases in mixing effectiveness were shown as the dimensionless screw pitch increased from 1.25 to 1.75, and statistically these two conditions could not be distinguished given the amount of data in this study. Results are compared to previous granular mixing measurement techniques found in the literature, and similar results are reported.

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