Incompressible Model of Solids Conveying in a Single-Screw Extruder

Abstract

Experiments in corn meal extrusion [Zhang, S. and Sernas, V. (1998). Proc. 1998 ASME Int ME. Congress and Exposition, Anaheim, CA, HTD-Vol. 361-1. pp. 309-315] have shown that the flow of solids in the screw channel of a single-screw extruder has a helical pattern. This observation implies that there is a cross-channel velocity component in the solids conveying zone of the extruder. Existing solids conveying models [Broyer, E. and Tadmor, Z. (1972). Polym. Eng. Sci., 12(1): 12-24; Campbell, G.A. and Dontula, N. (1995). International Polymer Process X. Hanser Publishing. pp. 30-35; Darnell, W.H. and Mol, E.A. (1956). Soc. Plast. Eng. J., 12(4), 20-29; Hyun, K.S. and Spalding, M.A. (1997). ANTEC ’97 Proc. 163: 211-218] treat the solids moving in the channel as a plug flow without a cross-channel velocity component. The two-dimensional powder conveying model proposed in this paper contains both a down-channel component and a cross-channel component. The stress generating mechanism is much more complicated in a powder flow than in a fluid flow. The incompressible model incorporates a constitutive equation for the powder flow with slip boundary conditions. The energy equation with appropriate boundary conditions is also included in the model.

The numerically solved model shows that the predicted down-channel pressure development, velocity and temperature distributions are all reasonable.

Keywords

solids conveying incompressible model slip boundary

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