Novel method for thermal conductivity measurement through flux signal deconvolution

• Transient heat flux technique for thermal properties of high conductivity solids.
• Combining the use of two heat flux measurements with short heat impulse.
• The fundamental model which describes the system is used as basis.
• Optimization is used to fit the measured system impulse response.
• Validated using two commercial metals, suitable for practical, composite systems.

Rapid thermal conductivity measurement of porous solids and composites remains a challenge. A modified steady state technique has been proposed which uses two heat flux sensors instead of one. The parameter estimation is achieved through the deconvolution of these signals and the identification of the system impulse response. A detailed derivation of the theoretically expected behaviour has been done, which provides a basis for fitting the measured impulse response. A six term expansion is required for the theoretical model to achieve full convergence. The unit requires a calibration step to measure the convective boundary condition. A signal validity check has been built into the approach through the use of the energy balance which detects any drift due to ambient losses or other factors. Through suitable choice of the mathematical algorithm rapid convergence of the non-linear fitting procedure is achieved. The parameter estimates of the standard test samples are excellent, with average errors of 2.3% for brass and 6.3% for aluminium. The system has several advantages in addition to the short measurement time, including low cost and no guard furnace or insulation requirement for room temperature measurements. The approach is suitable for measuring the overall behaviour of practical, composite systems.