AN INSTRUMENT FOR THE MEASUREMENT OF THE THERMAL-CONDUCTIVITY OF LIQUIDS AT HIGH-TEMPERATURES

An instrument based on the line source method has been developed for the measurement of the thermal conductivities of liquids at high temperatures. The AC technique adopted utilizes a novel transformer bridge to provide the complete ground isolation needed for high temperature measurements. The method is used as a relative technique to minimize 'end effects', and used in this manner the results obtained for n-heptane and para-xylene were within +/- 2.5% of the accepted values. The use of AC power also allows the instrument to be used for measurements of ionically conducting liquids, the results obtained being within +/- 3% of recent values obtained using probes coated with Ta2O5. Thermal conductivity values derived for molten KNO3 were in agreement with the data obtained using steady state methods when the latter were corrected for radiation conduction effects. This suggests that the radiation conductivity contribution is small for the results obtained in the present investigation.