What is the best design for transferring bulk, friable materials from, say, from an upper bin (or process) to a lower bin? A while back I saw a pipe-in-pipe (rigid pipes since the height is fixed) system, solids flowed down in the annular area between the outer surface of the inner tube and the inner surface of the outer tube, thereby reducing velocity to a great extent, but I cannot find the vendor. Thanks in advance. ■