Technique For Measurement Of Thermal Conductivity Research Articles

微小重力環境を用いた溶融半導体の熱伝導率測定技術の開発

微小重力環境を用いた溶融半導体の熱伝導率測定技術の開発

A differential calorimetric technique for heat capacity and thermal conductivity measurements of liquids

Details are reported for a differential calorimetric technique to measure both the heat capacity and the thermal conductivity of liquid samples. The accuracy of the measured heat capacity is better than 0.4%, while sensitivity is about 4×10−4 J/°C. The accuracy of the measured thermal conductivity kL is about 1% if the difference between the kL value of the reference and the sample liquid is within 40%. Measurements were performed on: (a) water+t-butanol, (b) water+n-butanol, and (c) methanol+t-butanol mixtures at 25 °C. The experimental results for solute molar fraction x less than 0.2 are compared with data in the literature in the case of water+t-butanol mixtures. The heat capacity and thermal conductivity data versus x are probably the first ones published for mixtures (b) and (c).

Thermal diffusivity measurement by the transient hot-wire technique: A reappraisal

The theory of the transient hot-wire technique for thermal conductivity measurements is reassessed in the special context of thermal diffusivity measurements. A careful examination of the working equation and an error analysis are employed to identify the principal sources of error. Notwithstanding earlier claims to the contrary, the best precision that can be attained in thermal diffusivity measurements is of the order of ±3%, while the accuracy is inevitably poorer. Experimental evidence is adduced from two different instruments that supports the analysis given here. Although the technique cannot yield values of the thermal diffusivity, k, as accurate as can be achieved by the use of the best possible individual values of λ,ρ, and Cp in the relation k=λ/ρCp, the simplicity of the technique makes it attractive for many purposes. It is even possible to derive values of the isobaric heat capacity Cp for many fluids not available from other methods.

Generalised hot-wire technique for high pressure thermal conductivity measurements

The application of the generalised hot-wire technique to high pressure thermal conductivity measurement is discussed. Results for the thermal conductivity of NaCl obtained with a wire sandwiched between two homogeneous discs, one of NaBr and one of NaCl, were recorded in the pressure range 0-4 GPa. The results obtained are compared with those for a homogeneous cell. This comparison indicates that the generalised hot-wire technique appears to be applicable to high pressure thermal conductivity measurement. However, the errors in the generalised technique are larger than those in the standard technique.

A further contribution to the theory of the transient hot-wire technique for thermal conductivity measurements

Abstract The paper presents rigorous working equations for an automatic Wheatstone bridge employed in fluid thermal conductivity measurements by the transient hot-wire technique. Particular attention is concentrated upon the inevitable small differences between the two wires employed for the cancellation of the end effects in the experimental arrangement. It is shown that from experimental measurements of the change in the difference of resistance of the two wires as a function of time during their transient heating, it is possible to determine the temperature rise of a wire acting as a finite section of an infinite wire. The correct expressions for the calculation of the heat flux in the wire are also given.

Thermal conduction in a composite circular cylinder: a new technique for thermal conductivity measurements of lunar core samples

A new technique has been developed for the measurement of the thermal conductivity of lunar core samples. According to this technique, the core sample is heated radiatively from the outside at a known rate, the temperature is measured at the surface of the coretube, and the thermal conductivity of the sample is determined by comparing the measured temperature with the theory. The technique conforms with the aims of lunar sample preservation in that the sample remains intact after the measurements. The solution, as obtained in this paper, of a thermal conduction equation for a composite circular cylinder, with zero initial temperature and a constant heat-flux at its outer boundary, provides a theoretical basis for the present technique. Because of their mathematical similarity, the corresponding problems for a composite slab or sphere were also solved and the solutions are presented for possible future application to the thermal conductivity measurements. Testing demonstrated the feasibility of the new technique. The thermal conductivity of a simulant lunar soil sample, as determined by the present technique under vacuum conditions at about 300 K for sample densities of 1.47-1.67 g cm -3 , is 2.05-2.65 x 10 -3 W m -1 K -1 , which compares favourably with that of the same sample, 1.61-2.89 x 10 -3 W m -1 K -1 at sample densities of 1.50-1.75 g cm -3 , as measured under similar conditions by the standard line heat source technique. We describe in detail the experimental apparatus construction and procedure; in particular, the number of precautions taken to preserve the samples from disturbances and to improve the measurement results. This technique was successfully applied to the thermal conductivity measurement of two Apollo 17 drill-core samples. The results, 1.9-4.9 x 10 -3 W m -1 K -1 , which is intermediate between the values of thermal conductivity of the lunar regolith determined in situ (0.9-1.3 x 10 -2 W m -1 K -1 and those of lunar soil samples measured in the laboratory under simulated lunar surface conditions (0.8-2.5 x 10 -3 W m -1 K -1 ) presents an important clue to the understanding of heat transportation mechanisms in the lunar regolith.

A contribution to the theory of the transient hot-wire technique for thermal conductivity measurements

The paper presents rigorous working equations for an automatic Wheatstone bridge employed in fluid thermal conductivity measurements by the transient hot-wire technique. Particular attention is concentrated upon the inevitable small differences between the two wires employed for the cancellation of the end effects in the experimental arrangement. It is shown that from experimental measurements of the change in the difference of resistance of the two wires as a function of time during their transient heating, it is possible to determine the temperature rise of a wire acting as a finite section of an infinite wire. The correct expressions for the calculation of the heat flux in the wire are also given.

Variable temperature apparatus using a thermal conductivity measurement technique for the determination of superconducting ac power loss

A variable temperature apparatus is described which uses a thermal conductivity measurement technique for the determination of superconducting ac power loss. The technique consists of measuring the increase in temperature of a thermally isolated sample carrying an alternating current. Accurate measurements over a relatively large temperature range are possible. Loss data on a 13 cm long, single filament NbTi superconductor are presented at various temperatures and currents.

A Traversing-Thermocouple Technique for the Rapid Measurement of Thermal Conductivity in the Range 300 to 1200 K

A thermal conductivity measurement technique has been developed based on a novel design employing an ultrafine (0.02 cm dia) “traversing” thermocouple. This technique features the rapid determination of thermal conductivity as a function of temperature for specimens operating in the range from 300 up to 1200 K. In contrast to conventional “comparative” methods of thermal conductivity measurement, the present approach requires only one equilibrium condition, viz., the condition in which the specimen is maintained between the two temperature extremes of interest. The traversing-thermocouple measurement technique also permits the accommodation of a wide range of specimen sizes (e.g., 0.25 to 1.3 cm in diameter and 0.7 to 3.0 cm in length) and measurements accurate to within 5 to 7 percent. Although initially developed for use with semiconductors, the measurement technique is equally well suited to semimetals, metals, and insulators.

Application of the line-source technique for vacuum thermal conductivity measurements

Line source technique for ablative heat shield materials thermal conductivity measurements, comparing vacuum and atmospheric test results

Radiation Imaging Technique for Thermal Conductivity Measurement Above 1000°C

Imaging techniques and apparatus have been developed for measurement of thermal conductivity of small size samples at temperatures from 1000°C to the melting point of the material. Details of the method for heating the sample in an electric arc imaging furnace, measuring the temperature distribution over the sample surface with an optical pyrometer, and measuring the heat flux leaving the back of the sample with a thermopile are given. A computational procedure is described suitable for machine computer use.