Engineering context

Non-Newtonian fluids have a viscosity that changes with shear rate rather than staying constant, so their pressure drop and pump performance can differ markedly from a Newtonian liquid. They are modelled with the fluid defined in the database as a non-Newtonian liquid and its viscosity described by an appropriate rheology model.

The workflow starts by confirming the fluid is non-Newtonian — rheology test data showing shear-dependent behaviour confirms it, and for a slurry without test data, solids mostly 75 microns and smaller indicate a non-settling slurry with non-Newtonian characteristics (settling slurries belong on the settling slurry workflow). The fluid is defined in the fluid database as a non-Newtonian liquid and its viscosity described with the most appropriate rheology model — Power law, Bingham plastic, Herschel-Bulkley, or Casson. Boundaries are then added with the non-Newtonian fluid selected from the database (which carries its properties), operating conditions set, and the pressure model chosen correctly (stagnation for vessels, static for pipes or wall measurements). After building and connecting the network, the system is modelled as a liquid system with centrifugal pump non-Newtonian derating, then solved and analysed as a typical liquid system (velocity, capacity, NPSH margin) plus the drop in pump performance from non-Newtonian viscosity effects.

A non-Newtonian fluid has no single viscosity — it depends on shear rate — so pressure drop and pump duty cannot be predicted from one Newtonian viscosity value, and choosing the rheology model that matches the fluid’s measured behaviour is what makes the results meaningful.

Engineering workflow

1. Confirm the fluid is non-Newtonian. Rheology test data showing shear-dependent behaviour confirms a non-Newtonian fluid. For a slurry without test data, solids made up mostly of particles 75 microns and smaller indicate a non-settling slurry with non-Newtonian characteristics. (Settling slurries belong on the settling slurry workflow.)
2. Define the fluid in the database as a non-Newtonian liquid — define its properties in FluidFlow’s fluid database.
3. Define the viscosity using the most appropriate rheology model — Power law, Bingham plastic, Herschel-Bulkley, or Casson.
4. Define the boundary conditions. Add the boundaries and select the non-Newtonian fluid from the fluid database, which carries its properties; set the operating conditions (inlet pressure and flow, outlet pressure or flow), choosing the pressure model correctly — stagnation for vessels, static for pipes or wall measurements.
5. Build and connect the network — add pipes, fittings, elevations, and equipment, and connect them to establish topology, including any centrifugal pumps.
6. Model the system as a liquid system with centrifugal pump non-Newtonian derating — enable the option to derate centrifugal pump performance for non-Newtonian viscosity effects.
7. Solve, then analyse as a typical liquid system — review pipe velocity, capacity, and NPSH margin as you would for any liquid network.
8. Analyse pump performance — check pumps for the drop in performance due to non-Newtonian viscosity effects.

How FluidFlow helps

FluidFlow models these fluids within its steady-state pipe network solver, derating centrifugal pumps for non-Newtonian viscosity effects and reporting velocity, capacity, pressure drop, and NPSH across the connected network. It is not CFD and does not perform transient or particle-tracking simulation.

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