The influence of a bend on the flow characteristics in pneumatic conveying systems

Pneumatic conveying systems are widely used in the chemical, pharmaceutical, and food industries. The aim of these transport systems is to transfer particulate material between storage locations, or to feed different kinds of reactors. One of the advantages of using a pneumatic conveying system to transport a bulk particulate material, compared to other systems, is the flexibility in routing the pipeline. This often results in transport pipes with many bends, which considerably increase the difficulty in predicting the performance of the system. The importance of the number and location of bends in the design of pneumatic transport systems has been noted by many workers, for example Mills. The influence of a bend on the distribution of particles in a pipe cross-section of pneumatic conveying systems has been investigated numerically. The numerical model solved the finite-volume equations for the conservation of mass and momentum for two phases. It was evident that the cross-sectional concentration of the particles a few meters after a bend is not uniform and that the particles tend to concentrate around the pipe's wall. Various cross-sectional concentrations of particles are found for: different pipe to bend radius ratios; particles size; and direction of gravity (i.e. horizontal to vertical flow, and horizontal to horizontal flow). Based on the different cross-sectional concentrations for different particle sizes, it is concluded that the paths taken by the particles after the bend are strongly dependent upon their sizes. As a consequence, segregation of particles downstream of a bend is expected.