Average Heat Transfer Coefficients in Twin Screw Extruders

A procedure combining numerical and experimental techniques has been developed to estimate the average heat transfer coefficient for twin screw extruders. The procedure is based on the one‐dimensional heat transfer equation for a non‐Newtonian food dough. Experimental data were collected with 30 degree forwarding kneading discs to provide complete mixing and ensure a uniform temperature distribution in the direction perpendicular to the screw shafts. The average heat transfer coefficients were expressed in terms of the Brinkman and Graetz numbers, with excellent statistical correlation, Results obtained in this study are slightly higher than those reported in the technical literature for single screw extruders. However, the difference can be attributed to better mixing in the twin screw extruder, which enhances heat transfer.