Residence Time Distributions for Wheat Starch in a Single Screw Extruder

Authors

  • V. J. DAVIDSON,

    1. Authors Davidson and Diosady are affiliated with the Dept. of Chemical Engineering & Applied Chemistry, Univ. of Toronto, Toronto, Ontario, Canada, M5S 1A4. Authors Paton and Spratt are affiliated with the Food Research Institute, Agriculture Canada, Ottawa, Ontario, Canada, K1A 0C6.
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  • D. PATON,

    1. Authors Davidson and Diosady are affiliated with the Dept. of Chemical Engineering & Applied Chemistry, Univ. of Toronto, Toronto, Ontario, Canada, M5S 1A4. Authors Paton and Spratt are affiliated with the Food Research Institute, Agriculture Canada, Ottawa, Ontario, Canada, K1A 0C6.
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  • L. L. DIOSADY,

    1. Authors Davidson and Diosady are affiliated with the Dept. of Chemical Engineering & Applied Chemistry, Univ. of Toronto, Toronto, Ontario, Canada, M5S 1A4. Authors Paton and Spratt are affiliated with the Food Research Institute, Agriculture Canada, Ottawa, Ontario, Canada, K1A 0C6.
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  • W. A. SPRATT

    1. Authors Davidson and Diosady are affiliated with the Dept. of Chemical Engineering & Applied Chemistry, Univ. of Toronto, Toronto, Ontario, Canada, M5S 1A4. Authors Paton and Spratt are affiliated with the Food Research Institute, Agriculture Canada, Ottawa, Ontario, Canada, K1A 0C6.
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  • Contribution No. 521 from the Food Research Institute.

ABSTRACT

Residence time distributions for wheat starch in a single screw extruder were measured for different operating conditions using a manganese dioxide tracer. Two flow models which differed in the definition of dead space were used to represent the flow pattern in the extruder. The parameters for each model were fitted using the experimental residence time distributions. Screw speed and the moisture level of the feed showed the strongest effects on the average residence time. A small fraction of the flow, 5–20%, was held up in the dead space region. The remainder passed directly through the active region with a residence time distribution close to plug flow. An apparent power law index for the starch melt was calculated and over the experimental range of extrusion conditions it varied from 0.2 to 1.0.

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