A Novel Portable Absolute Transient Hot-Wire Instrument for the Measurement of the Thermal Conductivity of Solids

A new portable absolute Transient Hot-Wire instrument for measuring the thermal conductivity of solids over a range of 0.2$$\,\hbox { W}{\cdot }\mathrm{m}^{-1}{\cdot }\hbox {K}^{-1}$$W·m-1·K-1 to $$4\,\hbox { W}{\cdot }\mathrm{m}^{-1}{\cdot }\hbox {K}^{-1}$$4W·m-1·K-1 is presented. The new instrument is characterized by three novelties: (a) an innovative two-wires sensor which provides robustness and portability, while at the same time employs a soft silicone layer to eliminate the effect of the contact resistance between the wires and the sample, (b) a newly designed compact portable printed electronic board employing an FPGA architecture CPU to the control output voltage and data processing—the new board replaces the traditional, large in size Wheatstone-type bridge system required to perform the experimental measurements, and (c) a cutting-edge software suite, developed for the mesh describing the structure of the sensor, and utilizing the Finite Elements Method to model the heat flow. The estimation of thermal conductivity is modeled as a minimization problem and is solved using Bayesian Optimization. Our revolutionizing proposed methodology exhibits radical speedups of up to $$\times $$×120, compared to previous approaches, and considerably reduces the number of simulations performed, achieving convergence only in a few minutes. The new instrument was successfully employed to measure, at room temperature, the thermal conductivity of two thermal conductivity reference materials, Pyroceram 9606 and Pyrex 7740, and two possible candidate glassy solids, PMMA and BK7, with an absolute low uncertainty of 2 %.

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