Influence of insulation coating on thermal conductivity measurement by transient hot-wire method

The transient hot-wire method is widely used to determine the thermal conductivity of various media. It has been improved through the addition of an insulation coating to the wire. However, this coating could affect the accuracy of the thermal conductivity measurement. The temperature rise for the insulation-coated wire was calculated as a function of time by a Laplace transformation along with the expansion method outlined by Carslaw and Jaeger [Conduction of Heat in Solids (Oxford University Press, Oxford, 1959)]. The results of numerical simulations and experimental tests show that, for most engineering applications, the relative measurement errors of the thermal conductivity caused by the insulation coating are very small if the slopes of the temperature rise-logarithmic time diagrams are calculated for large time values. No correction to the insulation coating is necessary even for the conditions that the insulation coating thickness is comparable to the wire radius, and that the thermal conductivity of the insulation coating is lower than that of the measured medium.