The Properties of Combined Horizontal Flows of Air and Farm Livestock Slurries in a Tubular Loop Aerator

Pig slurries and dairy cattle slurries exhibit shear-thinning characteristics and therefore two-phase horizontal pipeline flows of water and slurries with air were studied in a novel Tubular Loop Aerator (TLA) to determine whether air injection could achieve shear-thinning effects, leading to reduced energy requirements. The TLA incorporated a pipeline of 40·2 mm internal diameter which was 65 m in length. It was found that the pressure gradients resulting from these two-phase flows were described satisfactorily by a correlation based on ratios of single- and two-phase pressure gradients. This technique enabled convenient comparison of the flow characteristics of slurries with different total solids (TS) concentrations at different air injection rates. Pig slurries containing up to 3·5% TS showed no reductions in pressure loss due to air injection, whereas cattle slurries of 2–3% TS produced some instances of pressure reduction. These reductions occurred at low superficial liquid flow velocity (0·5 m/s) and <2% (vol/vol) air injected, but the results did not provide statistically significant evidence of an energy-saving effect.