The transient divided bar method for laboratory measurements of thermal properties
- 30 July 2016
- journal article
- Published by Oxford University Press (OUP) in Geophysical Journal International
- Vol. 207 (3), 1446-1455
- https://doi.org/10.1093/gji/ggw278
Abstract
Accurate information on thermal conductivity and thermal diffusivity of materials is of central importance in relation to geoscience and engineering problems involving the transfer of heat. Several methods, including the classical divided bar technique, are available for laboratory measurements of thermal conductivity, but much fewer for thermal diffusivity. We have generalised the divided bar technique to the transient case in which thermal conductivity, volumetric heat capacity, and thereby also thermal diffusivity are measured simultaneously. As the density of samples is easily determined independently, specific heat capacity can also be determined. The finite element formulation provides a flexible forward solution for heat transfer across the bar and thermal properties are estimated by inverse Monte Carlo modelling. This methodology enables a proper quantification of experimental uncertainties on measured thermal properties and information on their origin. The developed methodology was applied to various materials, including a standard ceramic material and different rock samples, and measuring results were compared with results applying traditional steady-state divided bar and an independent line-source method. All measurements show highly consistent results and with excellent reproducibility and high accuracy. For conductivity the obtained uncertainty is typically 1–3%, and for diffusivity uncertainty may be reduced to about 3–5%. The main uncertainty originates from the presence of thermal contact resistance associated with the internal interfaces in the bar. These are not resolved during inversion and it is imperative that they are minimized. The proposed procedure is simple and may quite easily be implemented to the many steady-state divided bar systems in operation. A thermally controlled bath, as applied here, may not be needed. Simpler systems, such as applying temperature-controlled water directly from a tap, may also be applied.Keywords
This publication has 22 references indexed in Scilit:
- Prediction of thermal contact resistance between polished surfacesInternational Journal of Heat and Mass Transfer, 1998
- Test measurements with a new thermal conductivity borehole toolTectonophysics, 1995
- A pulse method for studying thermal transport properties of sedimentary rocksTectonophysics, 1988
- The measurement of thermal diffusivity of rock coresTectonophysics, 1984
- A transient method and thermophysical parameters of rocks from Dobrudja, northeastern BulgariaTectonophysics, 1984
- Generalized nonlinear inverse problems solved using the least squares criterionReviews of Geophysics, 1982
- The effect of environment on divided bar measurementsTectonophysics, 1970
- Thermal contact conductanceInternational Journal of Heat and Mass Transfer, 1969
- A steady state method for the rapid measurement of the thermal conductivity of rocksJournal of Scientific Instruments, 1957
- A Transient-Flow Method for Determination of Thermal Constants of Insulating Materials in Bulk Part I—TheoryJournal of Applied Physics, 1954