The flow of “settling” slurries in tubes with internal spiral ribs

Abstract

AbstractThe secondary flows created by an internal spiral rib in an otherwise conventional smooth tube are illustrated by reference to the axial, and combined tangential and radial velocity components for a fluid flowing in a 2‐inch diameter tube containing a rib with a pitch‐to‐diameter ratio of 3The effect of such secondary flows on the transportability of “settling”(suspensions)was investigated by measuring pressure gradients for the flow of two sand/water slurries in a smooth 2‐inch tube and in 2‐inch diameter tubes with ribs of pitch‐to‐diameter ratio 5.15, 3.32 and 1.80. Average flow velocities ranged from 0.5 to 8 feet/sec. and delivered concentrations ranged from 5 to 18 per cent by volumeWhile the ribs were found to be a disadvantage at relatively high average mixture velocities because of increased pressure gradients, they were found to be advantageous at relatively low velocities, i.e. velocities less than the critical deposit velocity for flow in the smooth tube, in that the pressure gradients, for a given sand/water slurry with a given delivered concentration and average velocity, were lower in the ribbed tubes than in the smooth tube. Because of this, the power consumption per unit mass of solid transported was reduced by the presence of a rib. The optimum pitch‐to‐diameter ratio was estimated to be about 5Pressure gradients measured for one of the slurries with air added as a third phase showed the presence of air to be a definite disadvantage