Rheology

Rheology describes how a material flows and deforms under applied stress. In filtration engineering it captures the viscosity–shear relationship of process streams—from Newtonian liquids with constant viscosity to non‑Newtonian slurries that shear‑thin (pseudoplastic), shear‑thicken (dilatant), or exhibit a yield stress (Bingham or Herschel–Bulkley behaviour). Rheology governs pressure‑drop and flux: for a given medium and cake resistance, higher apparent viscosity raises ∆p at constant flow, while shear‑thinning inside pores can reduce the hydraulic load and delay blinding. Accurate design therefore requires rheometry across the relevant shear‑rate and temperature windows, not a single ‘catalogue’ viscosity. In crossflow systems, wall shear stabilises flux for pseudoplastics; in dead‑end or cake filtration, viscosity controls cake build, washing and deliquoring. Temperature is a powerful lever—warming a feed lowers viscosity but may change solubility and crystal habit. Upstream conditioning (coagulation/flocculation) alters apparent rheology by creating open flocs that flow more easily and form permeable cakes. For predictable B2B operation, specifications should include rheological models and coefficients, shear‑history effects (pump and mixer profiles), and acceptance ranges, so control systems can maintain operating envelopes for TMP, flux and energy per unit throughput.