2017-2-1-Rheology.pdf - Food Science 500B Fall 2017...

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Food Science 500B Fall 2017 Rheology
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Viscosity Rheology is the study of flow Viscosity describes the resistance to flow Flow is a kind of deformation Different fluids exhibit different resistance to flow and they have different viscosities
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Viscosity Viscosity = Shear stress/Shear rate Shear stress=Force/Area The shear stress acts parallel to the flow Shear rate Velocity gradient ∆u/∆r = du/dr
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Food Rheology Where, τ is in Pa (N/m2) γ˚ is in 1/s μ is in Pa-s. Fluids that follow above equation are called Newtonian fluids Fluids that do not follow above equation are called Non Newtonian fluids. y u A F D D - = μ o g μ t =
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Classification of non-Newtonian Fluids Singh & Heldman (2009)
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Rheological Flow Curves Singh & Heldman (2009)
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Food Rheology Yield stress
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Herschel-Bulkley Model where, τ = Shear stress (Pa) γ o = Shear rate (1/s) τ y = Yield stress (Pa) m = consistency coefficient (Pa s n) n = power law/flow index (dimensionless) y n o m t g t + = ) (
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Examples of non-Newtonian Fluids Singh & Heldman (2009)
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Power Law Model Where, τ = Shear stress (Pa) γ o = Shear rate (1/s) m = consistency coefficient (Pa s n) n = power law/flow index (dimensionless) n o m ) ( g t =
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