Effect of a combination of two elbows on particle roping in pneumatic conveying

As gas and particles flow through an elbow in a lean phase pneumatic conveying system, the particles stratify into a relatively small portion of the pipe cross-section, forming a dense rope-like structure. Laboratory experiments and numerical simulations were carried out to determine the effect of two closely spaced elbows on roping behavior in a vertical pipe downstream of the second elbow. The results show that the combination of elbows results in a stationary rope which spirals around the inside of the vertical pipe, adjacent to the pipe wall. The angular position of the rope, peak particle concentration, and particle velocity in the rope were found to depend strongly on the length of the pipe connecting the two elbows. The results also show that the particle velocities in the rope are significantly lower in the case of two elbows than they are with a single elbow.