Residence Time Distributions for Wheat Starch in a Single Screw Extruder

Abstract

Residence time distributions for wheat starch in a single screw exnuder 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.

Digital image processing for measurement of residence time distribution in a laboratory extruder

“…However, the effect on variance was not quiet clear. Davidson, Paton, Diosady, and Spratt (1983), Lee and McCarthy (1996), Todd (1975), and Yeh et al (1991) had reported similar results. Increased screw speed may have resulted in more viscous heat dissipation, greater pumping force and more shearing, which enabled shorter MRT and better mixing of the material.…”

Xylose removal from lignocellulosic biomass via a twin-screw extruder: The effects of screw configurations and operating conditions

“…Decreasing the screw speed increases the residence time and induce a higher degree of fill. This effect pushes the biomass across restricting elements more slowly, thus higher pressures can be developed [4,30]. The SME did not seem to be affected by the screw speed (decreased torque at higher rotation) as shown in Fig.…”

Modeling residence time distribution in a twin-screw extruder as a series of ideal steady-state flow reactors

“…where (4) Hence, the four parameters that fully represent this model are t ‾, p, n and d. Other proposed models were described and compared by Davidson et al (1983).…”

“…The complete model is the most general model among all proposed models described in detail by Davidson et al (1983). The model represents the WolfResnich model when the plug flow fraction (p) is zero, the Levich model when n is very large and dead volume fraction (d) is zero, and the simplified model when the value of n is one.…”

“…Levich, Markin, and Chismadzhev (1967) developed a model for hydrodynamic mixing assuming an infinite series of continuously stirred tank reactors (CSTRs). Davidson, Paton, Diosady, and Spratt (1983) compared these proposed conceptual models to predict RTD in the single-screw extruder. Experimental RTDs were explained well with the models.…”