Screw reactors are gas/solid systems widely employed in industrial applications. Understanding the local powder mixing within these reactors is crucial, particularly at the reactor wall where wall/solid heat transfer occurs. This study proposes a non-invasive measurement method utilizing optical devices to assess wall particle motion. Two techniques for evaluating the particle motion are compared: a simple visual tracking method and particle image velocimetry. Both methods yield similar results, demonstrating consistent wall particle motion across the tube periphery during experimentation. The influence of operational and geometric parameters has been investigated, revealing that filling degree, powder flowability, and screw geometry significantly impact wall particle motion. Symbolic regression has been employed to derive dimensionless models that effectively predict experimental data. These models can be utilized to forecast wall particle motion, serving as a valuable tool for screw conveyor design.