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 paper is focused on the pulse transient method. The theory of the method and the measuring regime (time window) are analyzed. The results of the analysis are verified on borosilicate crown glass BK7, which is a candidate for a standard for thermal conductivity. Thermal contact and surface effects affect the length of the time window in which the evaluation procedure is applied. The one-point evaluation technique is compared with the results of the fitting procedure that uses the time window found by difference analysis. The values of the thermal conductivity, thermal diffusivity, and specific heat were found to be 1.05 W · m −1 · K −1 , 0.548 × 10 −6 m −2 · s −1 , and 767 J · kg −1 · K −1 , respectively, using the one-point evaluation technique.

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 .