OVERALL HEAT TRANSFER COEFFICIENT BETWEEN COOLING DIE AND EXTRUDED PRODUCT

Soy protein meat analog was produced using a twin-screw extruder with an attached cooling die. The experimental design consisted of two cooling die widths (30 and 60 mm), three cooling die lengths (100, 200, and 300 mm), four product moisture contents (55.8%, 61.6%, 67.0%, and 71.2% w.b.), and two cooling media (water or water plus ethylene glycol). The equivalent overall heat transfer coefficient (Ue) between extruded product and the cooling die was estimated based on three-channel split-flow heat transfer analysis. Product temperatures at the die outlet were predicted with the estimated value of Ue. The values of Ue were in the range of 0.217 to 0.423 and 0.215 to 0.408 kW/m2 K for water and water plus ethylene glycol, respectively, depending on the die width and feed moisture content. Predicted product temperatures at the die outlet were within 6.8°C of measured experimental values.