Measuring the diffusion coefficient of powder flow, which shows the magnitude of mixing, using X-ray visualization has been developed with the help of image processing techniques. Injecting minute metallic tracers into the powder yielded flow characteristics using the X-ray penetration images. The diffusion coefficient of the now was determined by tracer figure deformation with time. Using this method. we evaluated four kinds of powder flows transported using different shaped screws in a screw feeder unit. The following results were obtained from this investigation: (i) Increasing the pitch width of the screw yielded decreased transport velocity and a larger diffusion coefficient. (ii) Double screw provided the largest transport velocity and the smallest diffusion coefficient. In addition, uncertainty analysis was applied to the method of measuring the diffusion coefficient to achieve greater bias limit. (C) 2008 Elsevier B.V. All rights reserved.