Abstract
Fine powders \((10 ~\upmu \hbox {m}<d_{50}<100~\upmu \hbox {m}\)) behave analogously to liquids when aerated by air. Hence, methods (e.g. Couette method) used to determine the flow performance of liquids can be adopted to investigate the similar flow properties (e.g. apparent shear resistance) of aerated powders. By this means, the understanding and handling techniques for aerated fine powders can be significantly enhanced. This research aims to investigate the apparent shear resistance of aerated fine powders through a specialised viscometer. Such a viscometer is combined with a fluidisation system and a common rotary viscometer. Three types of fine powders (alumina, cement and flyash) were selected as testing materials. Experimental results indicated that aerated fine powders behave similarly to Herschel–Bulkley non-Newtonian fluids. Subsequently, the apparent shear resistance for three fine powders were modelled by modifying the original Herschel–Bulkley rheology model. Consequently, the apparent shear resistance of a specific aerated powder can be measured and modelled using the bench scale system developed in this study, thus can be utilised to predict the flow performance of fine powders in pneumatic conveyors.
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Abbreviations
- \(d_{50}\) :
-
Mean particle size (\(\upmu \hbox {m}\))
- \(\phi \) :
-
Cup diameter to bob diameter ratio
- \(v_\theta \) :
-
Velocity at \(\uptheta \) direction in the cylindrical coordinate system (m/s)
- \(\omega \) :
-
Angular velocity of the bob (rad/s)
- \(v_r \) :
-
Velocity at \(\hbox {r}\) direction in the cylindrical coordinate system (m/s)
- \(v_z \) :
-
Velocity at \(\hbox {z}\) direction in the cylindrical coordinate system (m/s)
- P :
-
Pressure (Pa)
- \(\rho _B \) :
-
Bulk density (\(\hbox {kg/m}^{3}\))
- T :
-
Torque at the bob (\(\hbox {N}\, \hbox {m}\))
- \(R_i \) :
-
Bob radius (m)
- \(R_0 \) :
-
Cup internal radius (m)
- L :
-
Bob length (m)
- \(\dot{\gamma }\) :
-
Shear rate (\(\hbox {s}^{-1}\))
- \(\varOmega \) :
-
Rotation speed (rpm)
- \(\tau \) :
-
Shear stress (Pa)
- \(\eta \) :
-
Herschel–Bulkley consistency index
- b :
-
Herschel–Bulkley flow index
- \(\tau _0 \) :
-
Herschel–Bulkley yield stress (Pa)
- \(\eta _{\rho _B}\) :
-
Bulk density dependent Herschel–Bulkley consistency index
- \(b_{\rho _B}\) :
-
Bulk density dependent Herschel–Bulkley flow index
- \(\tau _{0 _{\rho _B}}\) :
-
Bulk density dependent Herschel–Bulkley yield stress (Pa)
- \(\rho _t \) :
-
Transitional bulk density (\(\hbox {kg/m}^{3}\))
- \(\rho _s \) :
-
Solids density (\(\hbox {kg/m}^{3}\))
- \(\rho _{blp} \) :
-
Loose poured bulk density (\(\hbox {kg/m}^{3}\))
- \(v_f \) :
-
Superficial air velocity (m/s)
- \(\rho _c \) :
-
Critical bulk density (\(\hbox {kg/m}^{3}\))
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Acknowledgments
The author would like to thank the Centre for Bulk Solids and Particulate Technologies, The University of Newcastle, Australia, for authorising this publication which was partially presented at the 11th International Congress on Bulk Materials Storage, Handling and Transportation held in Newcastle 2013.
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Chen, W., Williams, K.C., Bunn, T.F. et al. Measurement and modelling of the apparent shear resistance for aerated fine powders. Granular Matter 17, 593–602 (2015). https://doi.org/10.1007/s10035-015-0582-0
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DOI: https://doi.org/10.1007/s10035-015-0582-0