(published in revised form 4 April 2005; published online 13 June 2005) A large-scale pipeline apparatus was used to investigate the effects of air injection on the properties of turbulent liquid flows in horizontal pipelines of different internal diameters (38
1, 50
8, 76
2 and 102 mm). The liquids included clean water, pig slurries with total solid concentrations up to 4
4% and dairy cattle slurries with total solid concentrations up to 5
5%. The superficial flow velocities were between 0
5 and 6 m/s and air injection rates ranged from 1 to 6% (v/v) at the point of injection.
Experimental data were collected in the form of corresponding values of flow rate and pressure gradient. These showed that air injection generally increased pressure gradients compared with the liquids flowing alone. However, inspection of the data indicated a tendency towards pressure gradient reductions if air is injected into cattle slurries containing more than 5
5% total solids.
It was shown that a simple linear model could represent the changes in pressure gradient brought about by air injection, and that this could provide a satisfactory procedure for the design of slurry pipelines with air injection.