Abstract
A novel in-line rheometer, called “Rheopac”, has been designed and built in order to study the rheological behaviour of starchy products or, more generally, of products sensitive to a thermomechanical treatment. It is based on the principle of a twin channel, using a balance of feed rate between each of them, in order to make local shear rate vary in the measuring section without changing the flow conditions into the extruder. A wide range of shear rate could be reached and measurements were performed more swiftly than with a classical slit die. The viscous behaviour of maize starch was studied by taking into account the influence of the thermomechanical history, which modified the starch degradation and thus led to important variations in the viscosity. Experimental results were satisfactorily compared to previously published models.
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Abbreviations
- E :
-
activation energy (J · mol−1)
- h :
-
channel depth (m)
- h 1 :
-
depth under the piston valve in channel 1 (m)
- h 2 :
-
depth under the piston valve in channel 2 (m)
- K :
-
consistency (Pa·sn)
- K 0 :
-
reference consistency (Pa·sn)
- L :
-
total channel length (m)
- L p :
-
length of the piston valve (m)
- MC:
-
moisture content (wet basis)
- n :
-
power law index
- N :
-
screw rotation speed (rpm)
- P 0 :
-
entrance pressure (Pa)
- P e :
-
pressure at the entry of the piston valve (Pa)
- Q 1 :
-
flow rate in channel 1 (m3 · s−1)
- Q 2 :
-
flow rate in channel 2 m3·s−1)
- Q T :
-
total flow rate (m3 · s−1)
- R :
-
constant of perfect gas (8.314 J·mol−1·K−1)
- SME:
-
specific mechanical energy (kWh · t−1)
- T :
-
temperature (°C)
- T a :
-
absolute temperature (K)
- T b :
-
barrel temperature (°C)
- T d :
-
die temperature (°C)
- T p :
-
product temperature (°C)
- w :
-
channel width (m)
- W :
-
energetical term (J·m−3)
- η :
-
viscosity (Pa · s)
- [gh 0]:
-
intrinsic viscosity of native starch (ml·g−1)
- [η]:
-
intrinsic viscosity (ml·g−1)
- \(\dot \gamma \) :
-
shear rate (s−1)
- \(\dot \gamma _1 \) :
-
shear rate in measuring section (s−1)
- \(\dot \gamma _{\max } \) :
-
maximum shear rate (s−1)
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Vergnes, B., Della Valle, G. & Tayeb, J. A specific slit die rheometer for extruded starchy products. Design, validation and application to maize starch. Rheol Acta 32, 465–476 (1993). https://doi.org/10.1007/BF00396177
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DOI: https://doi.org/10.1007/BF00396177