Question

A)Model the heat transfer system that occurs during the extrusion process and explain the types of heat transfer that occur during the process.

B)Mold material, material to be extruded, mold sizes, material size and section type, extrusion force, ambient temperatures, material temperature, etc. Calculate the heat loss to the environment by using the material-mold-environment heat flow path during the extrusion process by determining the material and process parameters yourself and choosing the conduction and convection constants of the material and environment correctly.

Answer 1

Extrusion can be briefly described as a process where the material which is moistened, expandable in nature along with the proteinacious materials are plasticised and cooked in a tube by combination of moisture, pressure, temperature and mechanical shear. Extrusion is a processing technique' that involves the addition of thermal and mechanical energy to an uncooked mass such as soybean, wheat flour etc.. Extrusion processing is used to restructure the starch and protein based material to manufacture quality products. It involves compressing, working raw materials e.g., flours, starches, proteins, salt, fat, vitamins and minerals and other ingredients to form a semi-solid mass under a variety of controlled conditions.

Energy can enter the extruder in three ways. -

Convection: Steam contributes part of the cooking energy by convection

Conversion: Friction between the screws and barrel on the ingredients will generate heat. Here mechanical energy is converted to heat.

Conduction: Additional energy may be supplied by conduction of external heat through the extruder barrel.