Effect of screw configuration and speed on the P estimate of residence time distribution flow models

S. Y. Lee

Abstract

Extrusion cooking of rice has gained popularity due to the expansion properties and mild flavour of rice. Rice meal (25% wb moisture) was extruded using a 30 mm corotating twin screw extruder. The temperature profile used was 30, 60, 100 and 130 °C along the extruder and 130 °C at the die section. Three screw configurations and five screw speeds ranging from 62.5 rpm to 162.5 rpm were used. Residence time distribution (RTD) is a useful means to quantify the flow pattern of material in an extruder. RTD was analysed using the red dye intensity of sodium erythrosin. The RTD flow was modeled by combining perfect mixed flow and plug flow where P estimate (the fraction of material in plug flow) equaled to 0.5 and 1.0 respectively. In this study, the flow through the extruder was modeled by P estimate in the range of 0.41–0.55. Screw speed was found to have a significant effect on the P estimate.

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