Abstract
In this paper the design of a cut bar system to determine the thermal conductivity of conductive solid materials is presented. The system works under the comparative method, therefore two reference samples with known thermal conductivity are needed. The thermal design consisted on defining the physical configuration of the thermal system, materials to use and their dimensions, in order to evaluate their thermal performance by varying these parameters to calculate the maximum percentage design error. Given that the thermal design was parametric, the finite volume method was used to solve the heat conduction equation in the cut bar system, which allowed us to vary the different parameters that make up the thermal system such as length and diameter of the bars, insulation thickness, type of reference material, etc. The numerical code developed was verified with one analytical solution. It was found that, the thermal design of a cut bar instrument to determine the thermal conductivity of solid materials within the interval 0.58 ⩽ λ ⩽ 429 W.m-1 .K-1 shows a maximum design error of 3.77% associated to the length of the sample material. The results in this paper allow one to kwon the error by design which can be taken into account as a source of uncertainty when determining the thermal conductivity of solid materials.
Highlights
The thermophysical properties are divided into two different categories: thermodynamic and transport properties
Based on the study of heat transfer focused on the thermal design of a cut bar instrument to determine the thermal conductivity of solid materials, the following conclusions are presented: (a) Effect of the insulation material: it is recommended to use the maximum thickness for the insulation material 87.5 mm when the thermal conductivity of the sample material lies between 0.58 to 14.2 W.m−1.K−1; using this thickness the maximum percentage design error is 2.11%
For sample materials with thermal conductivity higher than 52 W.m−1.K−1 any length can be used (25 ZM 100 mm), in these cases, the error can be taken as constant with a value lower than 0.10%
Summary
The thermophysical properties are divided into two different categories: thermodynamic and transport properties. Thermodynamic properties such as density (ρ) and specific heat (Cp) are related to the equilibrium of a system. The thermal conductivity of a solid can be four times higher in magnitude than the conductivity of fluids (Fig. 1) [1]. Several methods to measure the thermal conductivity of different solid materials have been developed. The making and use of new materials, and the importance of their application aiming to more accurate results, have improved the already known methods and the development of new techniques to determine thermal conductivity
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