An experimental study on head loss characteristics of pipe bends for flow of coal-water slurry at high solid concentration

Bending of pipes is a major problem facing the engineers during the construction of a long pipeline for transporting coal-water slurry. However, the use of 90 degrees bends in slurry transportation is restricted because it causes high head loss, and so very high pumping power is required to overcome this resistance. In this context, the present study is carried out to reduce the head loss for the flow of coal-water suspension across 90 degrees pipe bends by varying bend geometry. Rheological experiments were performed to study flow characteristics of coal-water suspension with/without the additive. Coal-water slurry exhibits Newtonian behavior at a solid concentration of 30 wt% and pseudoplastic flow nature at concentration above 30%. Head loss experiments were carried out on a pilot plant test loop for a solid concentration of 30.27-61.56% with flow velocity ranging from 2 to 5 m/s. The r/D ratio for the pipe bend varied within the range of 1.5-2.5. The present study reveals that the head loss across pipe bends increased as solid concentration and flow velocity was increased. The optimum r/D ratio value for a minimum head loss was found to be 2.0. Also, significant decreases in apparent viscosity and head loss were perceived with the addition of a small amount of sulfonic acid. Power required to pump coal-water slurry was decreased by 15.93% with the use of an additive. A correlation for the head loss in terms of solid concentration, flow velocity, and r/D ratio was also developed.