Design and Fabrication of a System to Measure Thermal Conductivity of Compressible Materials

Abstract

Compressible materials are popularly applied in thermal insulation applications. Measuring the thermal conductivity of those materials is a challenge. Existing measuring methods are mostly focused on measuring the thermal conductivity of rigid materials. It causes in-accuracies due to several reasons such as externally applied pressure, change of dimensions of the specimen, and change of density of the specimen while being tested in the case of compressible materials. Therefore, in this research work, a dedicated concept of measuring the thermal conductivity of compressible materials was developed and fabricated a device complying with the industry standards. According to the literature review which was conducted initially, several thermal conductivity measuring devices which can be possibly used for compressible materials were identified. Based on the literature review, several conceptual designs were finalized. A heat flow meter apparatus that is currently available at the author’s affiliation was then studied and tested to identify the inaccuracies and difficulties of the heat flow meter method when utilizing incompressible materials. From all the conceptual designs developed, a concept similar to the hot wire method was identified and developed as a steady-state method. A mathematical model for the finalized concept was then developed based on the theories of heat transfer. A computer simulation was also done by using ANSYS simulation software to identify the design parameters of the device. Finally, the device was fabricated and tested for accuracy using a coirbased composite. Thermal conductivity tested with the currently available heat flow meter of compressible coir-based composite material was less than 0.5 𝑊/𝑚𝐾. For the same material, the method developed by this project gave an acceptable thermal conductivity value which is 0.211 𝑊/𝑚𝐾.