Temperature distribution measurement and control of extrusion process by tomography

Polymer extrusion molding is an important process in the polymer manufacturing industry. It is crucial to measure and control the temperature of polymer melt. Although different techniques, such as thermocouple, infrared and ultrasonic, have been attempted to measure the temperature, there is no suitable means so far to measure the internal temperature in a cross section of a polymer extrusion process, and hence the process is operated by trail-and-error. Electrical capacitance tomography (ECT) is a non-intrusive and non-invasive technique to obtain permittivity distribution of a cross section. Because the permittivity is a function of temperature for a certain material, if the extrusion chamber is fully occupied by polymer, the temperature distribution can be derived from the permittivity distribution, which can be obtained by ECT. This paper reviews the existing methods to measure the temperature of polymer melt first. The approach and the key issues to measure the temperature distribution based on ECT will be discussed in detail.