Finite-elements design of a guarded heating cylinder to measure thermal properties of materials

A device for the measurement of thermal properties of phase change materials and, in general, of medium thermal conductivity materials, is described. The measuring cell is a modified version of the guarded hot plate technique, here designed for about 8-cm-diam samples. A well-known difficulty arises in such a device: its limitation when the sample cross section becomes too small with respect to its thickness. A finite-element model is used to study the shape of isotherms in a thick sample (10 cm) for different configurations of the measuring device. This analysis has led to the selection of the optimum design. It shows that the instrument is able to handle samples with a diameter to thickness ratio of about 1 so far as the heat transfer coefficient remains beneath some limits (here 100 W/m2 K). The control system is also described and some typical results are presented. Review of Scientific Instruments is copyrighted by The American Institute of Physics.