An absolute method for determination of thermal conductivities of thermal insulators by microcalorimetry

Abstract

Microcalorimetry was developed to determine thermal conductivities (λ) of thermal insulators with hollow cylindrical shapes. A special device of specimen with resistance threads wrapped on its surface and electric heater placed in its hole was designed to meet the needs of determining λ without using standard substances to calibrate the instrument. A formula for calculating the value of λ was derived. By heating in the hole and on the surface of the specimen respectively, the values of λ can be obtained conveniently by this technique. The method was tested with teflon, plexiglass, quartz glass and polyethylene. The experimental values of λ for the four substances agree well with the literatures ones. Error analysis was also made on the experimental data. It was found that the main factors affecting values of λ are: (1) The errors of determining the values of heat cumulated in specimen and materials in the space around it and (2) the errors of determining the values of inner and outer radii of cylindrical specimen.