Turbulent pipe-fitting losses in thickened waste activated and digested sludges pipeline transport

Accurate estimation of minor losses due to pipe fittings such as valves, bends, contraction and expansions in pipelines is essential for the efficient transport of highly concentrated wastewater sludge (HCWS) in treatment facilities, yet experimental data for conventional fittings remain scarce. This study presents a systematic investigation of loss coefficients for four common fittings: plug valve, knife valve, gradual contraction and expansion, and bypass section, under high-Reynolds-number turbulent flow conditions. Experiments were conducted using digested sludge (DS) and thickened waste-activated sludge (TWAS) at solids concentrations ranging from 2–6 wt.% TS in a purpose-built pipe loop rig at Melbourne Water’s Eastern Treatment Plant, Australia. Sludge rheology was characterized using the Herschel–Bulkley model and fitting loss coefficients following correction for straight pipe frictional losses sections. indicate that, within turbulent regimes, fitting loss coefficients for both DS and TWAS converge toward near-constant values and remain close to those predicted by Newtonian correlations. However, combined fittings, such as contraction–expansion units and multi-bend bypass sections, exhibited substantially higher losses than the sum of their individual components. This work fills a critical gap by systematically quantifying turbulent fitting loss coefficients for both TWAS and DS under controlled, fully turbulent conditions. These findings provide first experimental benchmarks for minor fitting loss coefficients in concentrated sludge systems, facilitating more accurate pipeline design and energy optimization in wastewater sludge treatment infrastructure. • First turbulent minor-loss data for DS and TWAS across four pipe fittings. • Sludge loss coefficients match Newtonian values at high Reynolds numbers. • Loss coefficients largely independent of sludge type and solids content. • Combined fittings show elevated losses due to flow-interaction effects. • Provides benchmarks for accurate sludge pipeline and pump design.