An Improved Application of the Transient Hot-Wire Technique for the Absolute Accurate Measurement of the Thermal Conductivity of Pyroceram 9606 up to 420 K

Abstract

This article describes the final refinements of a novel application of the transient hot-wire technique developed for the absolute, accurate measurements of the thermal conductivity of solids. Although the technique was originally developed five years ago, these new refinements allow a full understanding of the method and hence the performance of measurements with an absolute uncertainty of less than 1 %. New measurements of Pyroceram 9606 up to 420 K are reported. The maximum deviation of the present measurements is 0.54 %, while their standard deviation at the 95 % confidence level is 0.25 %. Since May 2007, Pyroceram 9606 is a European Commission certified thermal-conductivity reference material, designated as BCR-724, with an uncertainty of ±6.5 % at the 95 % confidence level.

New Measurements of the Thermal Conductivity of PMMA, BK7, and Pyrex 7740 up to 450K

“…As already discussed elsewhere [6], an advantage of the proposed configuration is that it can also be employed to measure the thermal conductivity of fluids. Liquid toluene has been proposed by the Subcommittee on Transport Properties of the International Union of Pure and Applied Chemistry as a standard thermal-conductivity liquid with an uncertainty of 0.6 % [11].…”

“…The actual instrument employed for the measurement of the thermal conductivity of solids at elevated temperatures, with all its new refinements, is described elsewhere [6].…”

“…In order to eliminate end effects, two 5 µm diameter wires differing only in length are employed. In the specific case of measurements of the thermal conductivity of solids [6], in order to minimize contact resistance between the wire sensor and the solid, the wire sensor is placed inside a flat layer of soft silicone paste, which in turn is squeezed between two blocks of the solid. A very thin Kapton film between the soft silicone paste and the solid blocks, ensures the sensor's ease of assembly.…”

“…-the thickness of the paste (which, in the new sensor, is set exactly equal to 1 mm by the use of steel spacers [6]) -the paste's thermal conductivity and (density × specific heat capacity) product, and -the solid's thermal conductivity and (density × specific heat capacity) product.…”

“…In 2008, Assael et al [6] published further refinements of the technique reducing its uncertainty <1 %. Following these refinements, in this article the thermal conductivity of PMMA, BK7, and Pyrex 7740 is remeasured as a function of temperature.…”