Diffusion is a parameter often considered in mixing analyses. A distributed resistance in a mixing model simulates a physical device that has very different diffusion characteristics compared to the surrounding fluid. The result is that it affects mixing differently than the fluid.
To modify the diffusion characteristics of the distributed resistance region, enable this flag, and specify the ratio of the diffusion of the resistance region to the surrounding fluid. This characterizes how much less diffusive the resistance region is compared to the fluid.