Coarse solids in horizontal flow

The flow behaviour of suspensions of coarse particles is completely different in horizontal and vertical pipes. In horizontal flow, the concentration of particles increases towards the bottom of the pipe, the degree of non-uniformity increasing as the vel ity of flow is decreased. In vertical transport, however, axial symmetry is maintained with the solids evenly distributed over the cross-section. The two cases are therefore considered separately. 

Only with fine solids are the particles uniformly distributed over the cross-section of a horizontal pipe. For coarse particles, the following principal types of flow are observed as the velocity is decreased  

In addition, it is possible to obtain what is known as dense phase with the 

In ail cases where the two phases are moving with different velocities, it is important to differentiate between die concentration of particles in the pipe (their holdup 5) and the volume fraction of particles (C) in the discharge. The implications of this will now be considered, together with possible means of experimentally determining the holdup. 

It is not possible to calculate the in-line concentrations and slip velocity from purely external measurements on the pipe, i.e. a knowledge of the rates at which the two components are delivered from the end of the pipe provides no evidence for what is happening within the pipe. It is thus necessary to measure one or more of the following variables  

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