AbstractThe performance of cooling extruders widely used in thermoplastic foam extrusion was analyzed, by numerically solving the equations of motion and heat transfer. Analysis of cooling extruders does not require a consideration of the melting behavior of polymers, thus simplifying the system equations considerably. The flow geometry analyzed was an unwound screw channel of a single‐screw extruder, i.e., a rectangular channel of uniform height followed by diverging and converging sections. Due to the cooling of both the extruder barrel and the screw, the heat transfer equation considered includes the terms describing the convective heat transfer in the down‐channel direction and the conductive heat transfer in the cross‐channel direction, in addition to the terms describing the viscous shear heating. For the analysis, a power‐law model was used as the constitutive rheologlcal equation, describing the viscosities of a mixture of a fluorocarbon blowing agent and a low‐density polyethylene melt (or polystyrene melt). The parameters in the Theological model were determined using the data of Han and Ma (13). In obtaining numerical solutions of the equations of motion, an integration method was employed to overcome the problem of numerical instabilities. The present analysis predicts the profiles of developing temperature and velocity in the down‐channel direction, and the profiles of temperature, velocity, shear rate, and viscosity in the cross‐channel direction. In presenting the results of computer simulation, emphasis is placed on the effects of cooling the extruder barrel and screw on the performance of cooling extruders, in terms of the pressure drops along the extruder axis and the mechanical power consumption. This study provides a rational basis for the design of cooling extruders widely used in thermoplastic foam extrusion and for the selection of optimum extrusion conditions in producing thermoplastic foams.