Axial Heat Flow Methods of Thermal Conductivity Measurement for Good Conducting Materials

Abstract

The advantages of a longitudinal or axial heat flow method of thermal conductivity measurement over a radial method depend to a large extent on the temperature range to be covered and the types of specimen to be measured. In general, the former technique is more flexible in that a wide range of conductivity values can be covered (e.g., from about 5 W m^-1 K^-1 to 400 W m^-1 K^-1 in measurements above ambient temperature) by choosing the diameter of the specimen to suit the conductivity expected, sample preparation is relatively simple, material in rod form is normally readily available, the location of thermocouples in the specimen is easily determined, and suitable reference materials are available to check performance if required.^(1-3) On the negative side, heat losses due to radiation are more of a problem at high temperatures although they can usually be kept at a reasonable level if, in the areas where radiation is a problem, the temperatures of any shields are closely matched to the specimen temperature and a suitable insulation (density about 90 kg m^-3) is used between the respective parts.