Abstract
A knowledge of accurate data on thermal conductivity of liquids and gases is essential for optimal design of many engineering units. Only a few compounds have been studied and the investigations have been limited to temperatures below the normal boiling points. This paper discusses an improved transient hot-wire technique based on the perturbation of an ideal vertical line source with a ramp in power which signifies: (i) minimal free convection, radiation and Knudsen contributions to the apparent thermal conductivity, (ii) enhanced sensitivity to greater utilisation of the overall resistance change of the wire, and (iii) decreased capital cost relative to previous instruments due to use of a microcomputer. Based on a detailed mathematical model of this technique, an instrument has been designed and constructed. Thermal conductivity measurements on liquid toluene, a proposed standard, have proved the viability of the proposed technique. Results are in excellent agreement with the measurements of other investigators. The precision and accuracy of the results are estimated to be better than 0.8 and 1.1% respectively.