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Analysis of the dynamics of the FT4 Powder Rheometer featured in Powder Technology

"Analysis of the Dynamics of the FT4 Powder Rheometer®" by C.Hare, U.Zafar, M.Ghadiri, T.Freeman, J.Clayton and M.J. Murtagh is now available in the latest volume of Powder Technology.

The paper covers the following:

  • Dynamics of the FT4 Powder Rheometer for cohesive beads.
  • DEM predictions using particle properties compared with experimental data.
  • Simulations slightly underestimate experimental flow energy.
  • Flow energies using impeller or base downward forces are almost identical.
  • Shear stress is shown to be approximately constant across the blade length.


Traditional powder flow measurement devices, such as shear cells, operate in the quasi-static regime of shear strain rate. The FT4 Powder Rheometer of Freeman Technology, developed over the last two decades, has provided a clearer differentiation of powder flowability in some instances. This has been attributed to the instrument operating in the dynamic regime of shear strain rates, a feature that has yet to be established. We report an analysis of the dynamic behaviour of a bed of glass beads made cohesive by silanisation and subjected to standard FT4 testing procedure, where a rotating blade is driven into a cylindrical bed, using a combination of experimental measurements and numerical simulations by the Distinct Element Method (DEM). The DEM analysis underestimates the flow energy measured experimentally, although the agreement is improved when sliding friction is increased. The shear stress of the powder in front of the blade is shown to be roughly constant along the radial direction and increasing as the impeller penetrates the bed, suggesting that a characteristic shear stress can be determined for a powder under a given test condition in the FT4. For ease of simulations large beads were used (1.7–2.1 mm). Future work will investigate the influence of particle properties and operational conditions on the prevailing stresses and strain rates.

Read the full article here.