Dekusha O. Device for fast measurement of the thermal conductivity of solid materials.

The purpose of this work was to develop a new device, based on the steady state method of local heat influence, which is characterized not only by sufficiently high accuracy, wide range of measured values of coefficient of thermal conductivity, short time of sample preparation and measurement, but can measure samples of porous, low density materials. The method of local heat influence for determination of the coefficient of thermal conductivity is based on applying a heat flux of constant density to the material sample surface through a limited zone, the diameter of which is considerably smaller than sample size. In a steady thermal state, the coefficient of thermal conductivity can be found from measurements of the heat flux density and the temperature difference between the centre of the zone and the sample surface, where the heat does not influence the temperature. The influence of such factors as the convective-radiative heat exchange with the surrounding environment and contact thermal resistance between sample and probe is analytically studied. The influence of contact heat resistance becomes considerable at ? >0,2 W/(m·K). Therefore, the contact greases or additive temperature transducers are recommended for the investigations of solid materials. The instability of heat exchange is considerable at investigation of the samples with thermal conductivity ? <0,2 W/(m·K). In order to eliminate this instability, the special screen of low emissivity factor should be used, and the device should be placed under the sample. The influence of temperature drift can be diminished by constructing the device with two identical measuring heads, located more than 5 times the radius of the probe. The correction values for measurements of thermal conductivity on samples with thickness from 10 to 100 mm was calculated. The measurement time with the new device is about 25 minutes. The thermal conductivity of several types of modern insulating materials was investigated using the developed device.