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A Computational Technique for Turbulent Flow of Wastewater Sludge
Author(s) -
Bechtel Tom B.
Publication year - 2005
Publication title -
water environment research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.356
H-Index - 73
eISSN - 1554-7531
pISSN - 1061-4303
DOI - 10.1002/j.1554-7531.2005.tb00301.x
Subject(s) - turbulence , hydraulic head , computational fluid dynamics , mechanics , wastewater , pressure drop , flow (mathematics) , head (geology) , velocity gradient , shear stress , rheology , volumetric flow rate , materials science , geotechnical engineering , environmental science , engineering , environmental engineering , geology , physics , composite material , geomorphology
A computational fluid dynamics (CFD) technique applied to the turbulent flow of wastewater sludge in horizontal, smooth‐wall, circular pipes is presented. The technique uses the Crank−Nicolson finite difference method in conjunction with the variable secant method, an algorithm for determining the pressure gradient of the flow. A simple algebraic turbulence model is used. A Bingham‐plastic rheological model is used to describe the shear stress/shear rate relationship for the wastewater sludge. The method computes velocity gradient and head loss, given a fixed volumetric flow, pipe size, and solids concentration. Solids concentrations ranging from 3 to 10% (by weight) and nominal pipe sizes from 0.15 m (6 in.) to 0.36 m (14 in.) are studied. Comparison of the CFD results for water to established values serves to validate the numerical method. The head loss results are presented in terms of a head loss ratio, R hl , which is the ratio of sludge head loss to water head loss. An empirical equation relating R hl to pipe velocity and solids concentration, derived from the results of the CFD calculations, is presented. The results are compared with published values of R hl for solids concentrations of 3 and 6%. A new expression for the Fanning friction factor for wastewater sludge flow is also presented.