Rheological characteristics of concentrated Indian coal ash slurries and flow through pipelines

The present study investigates concentrated coal ash slurries' rheological and pipe flow characteristics. Our results reveal coal ash slurries' shear thinning flow behavior regardless of solid volume fraction (ϕ) = 0.17–0.6. Rheo-microscopy study explains the thixotropy, yielding where slurry microstructure varies with time and applied shear. Experimental viscosity data fit with Dabak and Yucel model with a maximum coal ash packing fraction (ϕ<inf>m</inf>) = 0.63. The yield stress (τ<inf>y</inf>) determined using the creep test, stress sweep, Herschel-Bulkley model, and oscillatory sweep tests indicate the exponential relationship of τ<inf>y</inf> with ϕ = 0.43–0.6. The head loss (h<inf>L</inf>) during pipeline transportation of slurries increases with coal ash concentration (ϕ = 0.272–0.349) and slurry velocity (v<inf>m</inf> = 0.5–3 m/s). h<inf>L</inf> estimated from the rheological data is comparable with the experimental pipe-loop data with pipe length, L = 12 m, and pipe diameters, D = 25 and 50 mm at higher v<inf>m</inf> (∼2–3 m/s).