The objective of this work is to improve measurements of transport properties using the hot disk thermal constants analyzer. The principle of this method is based on the transient heating of a plane double spiral sandwiched between two pieces of the investigated material. From the temperature increase of the heat source, it is possible to derive both the thermal conductivity and the thermal diffusivity from one single transient recording, provided the total time of the measurement is chosen within a correct time window defined by the theory and the experimental situation. Based on a theory of sensitivity coefficients, it is demonstrated how the experimental time window should be selected under different experimental situations. In addition to the theoretical work, measurements on two different materials: poly͑methylmethacrylate͒ and Stainless Steel A 310, with thermal conductivity of 0.2 and 14 W/mK, respectively, have been performed and analyzed based on the developed theory.

A version of a transient method for measuring specific heat, thermal diffusivity and thermal conductivity is presented. The dynamic temperature field is generated by the passage of the electrical current through a planar electrical resistance made of thin metallic foil. The heat is produced in the form of a step-wise function. A thermocouple placed apart from the heat source measures the temperature response. The theory of the method, its experimental arrangement and the measuring regime for considering sensitivity coefficients are presented. Experimental data obtained on Perspex are compared with recommended and published data. The data on thermal conductivity agree to within ±0.7% whereas the specific heat is lower on average by 5.2% and the thermal diffusivity is higher by 3.5% when measurements were realized in vacuum. A shift in data of up to 10% was found for measurements made in air.

This article deals with the theory and performance of a sensor for measuring thermal conductivity. The sensor, in the form of a small ball, generates heat and simultaneously measures its temperature response. An ideal model of the hollow sphere in an infinite medium furnishes a working equation of the hot-ball method. A constant heat flux through the surface of the ball generates the temperature field. The thermal conductivity of the surrounding medium is to be determined by the stabilized value of the temperature response, i.e., when the steady-state regime is attained. Error components of the sensor are discussed due to analysis of the deviations of the real hot-ball construction from the ideal model. The functionality of a set of hot balls has been tested, and the calibration for a limited range of thermal conductivities was performed. A working range of thermal conductivities of tested materials has been estimated to be from 0.06 W · m −1 · K −1 up to 1 W · m −1 · K −1 .

A new model for the sample of square cross section with cuboid geometry including the effect of heat loss from the surface of the sample was tested using the theory of sensitivity coefficients. Theoretical calculation of model uncertainty and derived analytical formulas are presented. Results of the uncertainty analysis set out the range of experimental conditions under which the model is valid and the uncertainty of estimated parameters is low. Propagation of error for non-stochastic dynamic measurements based on the sensitivity coefficients shows limitations related to a range of model validity. The analysis improves the accuracy of measurements. The model was used for data evaluation of thermophysical parameters measured on the sandstone from the locality Pravčická brána. Evaluation procedure was tested on experimental data measured under different experimental conditions. In conclusion, the discussion of the experiment optimization is presented.