Silas E. Gustafsson

Transient plane source techniques for thermal conductivity and thermal diffusivity measurements of solid materials

The general theory of the transient plane source (TPS) technique is outlined in some details with approximations for the two experimental arrangements that may be referred to as ‘‘hot square’’ and ‘‘hot disk.’’ Experimental arrangements and measurements on two materials, Cecorite 130P and Corning 9606 Pyroceram, using a hot disk configuration, are reported and assessed.

Transient hot-strip method for simultaneously measuring thermal conductivity and thermal diffusivity of solids and fluids

A transient hot-strip method has been developed for use with solids and fluids with low electrical conductivity. The hot strip (thin metal foil) is used both as a constant plane heat source and a sensor of the temperature increase. The accuracy of the method is so good that it might even be used for the measurement of the specific heat especially under difficult experimental conditions when the standard methods cannot be used or would be very inconvenient. This method has been tested in measurements on fused quartz, glycerine and Araldite at room temperature. The experimental conditions that cause deviations from the mathematical solution of the thermal conductivity equation are discussed and estimates for their maximum influence on the measured quantities are given.

Thermal transport studies of electrically conducting materials using the transient hot-strip technique

The transient hot-strip (THS) method has been used for thermal conductivity and thermal diffusivity studies of electrically conducting materials by introducing a thin electrically insulating layer between the hot strip and the metallic material under study. The insulating layer introduces a certain thermal contact resistance between the hot strip (heat source cum temperature sensor) and the surface of the sample to be studied. To account for this thermal resistance a theory has been developed which indicates how measurements on these kind of materials should be performed and how the reduction of data from transient recordings should be carried out to give reliable results. The new experimental approach, which should be applied whenever a thermal contact resistance is suspected, has been demonstrated by two series of measurements on a stainless steel at room temperature.

Parameter estimations for measurements of thermal transport properties with the hot disk thermal constants analyzer

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: poly(methylmethacrylate) 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.

Determination of the thermal‐conductivity tensor and the heat capacity of insulating solids with the transient hot‐strip method

The recently described transient hot‐strip method has been developed for the study of solids with direction dependent thermal conductivity. By making three independent measurements, with the hot‐strip properly oriented, information can be obtained about the thermal conductivities along the principal directions and also about the specific heat capacity per unit volume. To demonstrate the versatility of the method, crystalline quartz was studied over the temperature range 230–340 K and the results are in good agreement with earlier reported data.

Transient hot‐strip probe for measuring thermal properties of insulating solids and liquids

The transient hot‐strip (THS) method has been developed for experimental situations with two different materials kept against the sides of the strip. Based on this development THS probes, with known or separately measured thermal properties, have been designed and used successfully in a series of reported experiments. If the thermal diffusivity of the probe is less than that of the material under study and good contact is established between the probe and the sample, the accuracy of the measurements turns out to be as good as with the ordinary transient hot‐strip method.

Transient hot‐strip method for measuring thermal conductivity and specific heat of solids and fluids: Second order theory and approximations for short times

The theory of the newly described transient hot‐strip method has been developed to include second order terms of the temperature dependence of the electrical resistivity of the hot strip. The theory indicates that second order terms should be included in situations where a high‐current pulse is being used. Approximate values of the coefficients for the second order terms have been determined numerically. For times appreciably less than the characteristic time, a simple approximation of the voltage variation as a function of time has been derived and tested experimentally.

Thermal properties of thin insulating layers using pulse transient hot strip measurements

A transient method for measuring thermal conductivity and thermal diffusivity has been developed for studies of insulating solid surface layers with thicknesses down to a few micrometers. The method is based on a procedure by which a string of square pulses, via an ac‐coupled circuit, is applied to the hot strip (deposited thin film), which is acting both as a heat source and a sensor of the temperature increase of the substrate. By performing transient experiments over short times (selecting a short pulse duration), it is possible to limit the depth under the hot strip beyond which the thermal properties of the substrate does not influence the recorded thermal properties. A series of experiment with probing depths ranging from 4 to 10 μm has shown that the thermal properties measured with this technique agree very well with independently measured values provided the pulse duration is small compared to the pulse period. Because of the small probing depth and the size of the thermal probe this novel techni...

Refractive Index Measurements in Fused NaNO 3 and KNO 3 by a Modified Thermooptic Technique

A thermooptic technique for studying the temperature dependence of refractive index of liquids at room temperature has been modified and applied to the study of molten NaNO(3) and KNO(3) within a temperature range of some 80 K above the melting point for five different wavelengths within the visible spectral range. The experiments show a temperature dependence of the polarizability for the two salts as calculated from the Lorentz-Lorenz formula, which cannot be explained by experimental inaccuracy.

Effective thermal conductivity of loose granular materials

A lattice type periodic model formed by finite-spaced point spherical interacting particles, as developed by Pande et al. (1984), is used for the estimation of effective thermal conductivity of loose granular materials, under the effective continuous medium approximation. Calculated values of effective thermal conductivity of these materials have been compared with experimental results. The results are in good agreement. The experimental methods used for the measurements of effective thermal conductivity of these materials are the Transient Hop Strip and Thermal Probe methods.