Precise measurement of thermal conductivity of liquid over a wide temperature range using a transient hot-wire technique by uncertainty analysis

One of the standard methods used to measure the thermal conductivity of liquids is transient hot-wire technique. The principle of this technique is to fit the unbalanced voltage of the hot wire in a bridge circuit using a theoretical model. The uncertainty in the measurement mainly relates to the procedure used and the measuring instruments, which we evaluate for toluene in liquid phase at atmospheric pressure and in the temperature range from −30 °C to 90 °C using the Guide to the Expression of Uncertainty in Measurement. The uncertainty of the results was estimated to be within ±0.50% below 60 °C and ±0.96% at a temperature of 90 °C. The maximum departure between recommended values and the results of our experimental runs is 0.31% at the highest temperature, and the thermal conductivity values measured are in good agreement with the recommended values within the level of uncertainty over the whole temperature range.