Measurement Techniques and Considerations for Determining Thermal Conductivity of Bulk Materials (original) (raw)
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Thermal Conductivity of Solid Materials
INTERNATIONAL JOURNAL OF RESEARCH IN ENGINEERING & SCIENCE
Thermo physical properties such as specific heat, thermal conductivity and density are unique for any material. Within a conductive material, thermal conductivity is the main property in the thermal energy transfer. Specific heat and density are the important components involved in the analysis of energy and mass balances. When combining these three properties, we get the thermal diffusivity, which is used in the analysis of unsteady-state heat transfer. Two major methods are used to measure the thermal conductivity of any material. The steady state method named guarded plate method which depends on a constant temperature difference achieved in the specimen of the material. This method needs complicated measurement system, it is unsuitable for the field application [1]. The transient (unsteady-state) techniques generally use a heater of a particular geometry inserted in the sample, and heated within a period of time. These measurement systems are less complex with respect to steady state methods and are better suited for field measurements. The experimental studies for determination of the thermal properties in a transient state has been conducted with numerous methods and techniques. The linear heat source method relies on a steady heat source ,for example, a hot wire, that generate s a temperature field inside an infinite volume of a material. Based on the thermal conductivity of the desired material, the temperature rise in its sample will vary from one material to other. The thermal conductivity, then, can be calculated from the temperature rise at two unique times and the power of the heater. This method was used to measure the thermal conductivity of many solids , fluids and soil [2-4].
Measurement of Thermal Conductivity
İn this experiment about to find thermal conductivity, which represents with "k".The rate of transfer of thermal energy. It has a broad application area ranging common household appliances, residential and commercial buildings, industrial processes, electronic devices, and food processing.
International Journal of Thermophysics, 2015
This paper presents a critical review of current industrial techniques and instruments to measure the thermal conductivity of thermal insulation materials, especially those insulations that can operate at temperatures above 250 • C and up to 800 • C. These materials generally are of a porous nature. The measuring instruments dealt with here are selected based on their maximum working temperature that should be higher than at least 250 • C. These instruments are special types of the guarded hot-plate apparatus, the guarded heat-flow meter, the transient hot-wire and hot-plane instruments as well as the laser/xenon flash devices. All technical characteristics listed are quoted from the generally accessible information of the relevant manufacturers. The paper includes rankings of the instruments according to their standard retail price, the maximum sample size, and maximum working temperature, as well as the minimum in their measurement range.
Thermal conductivity of materials for structural elements and thermal insulation represents a fundamental parameter in the assessment of the energy need of buildings. In this paper, two different systems for thermal conductivity measurement are compared, based respectively on the calibrated hot box and on the guarded hot plate methods. The study is specifically aimed at assessing the range of thermal transmittance where the hot box system is suitable and verifying the strengths and the weaknesses of the system. The comparison between measurements on specimens with different thermal conductivity and thickness showed that the two methods are substantially equivalent in the considered range of thermal conductivity, but are not completely interchangeable. In particular, the measurement campaign confirmed the expectation that the hot box system gives more accurate results with low thermal resistance samples.
International Journal of Thermophysics, 2012
For the first time under the auspices of the Bureau International des Poids et Mesures (BIPM), seven national metrology institutes (NMIs) participated in an international interlaboratory comparison on thermal-conductivity measurements by the guarded hot-plate method. Measurements were conducted successively by all participants on the same set of specimens of insulating materials (mineral wool and expanded polystyrene) at temperatures ranging from 10 • C to 40 • C, according to the International Standard ISO 8302. This protocol aims to minimize issues of material
Thermal Conductivity of Reference Solid Materials
International Journal of Thermophysics, 2000
The thermal conductivity of three thermal-conductivity reference materials, Pyrex 7740, Pyroceram 9606, and stainless steel AISI 304L, has been studied. The technique employed is the transient hot-wire technique, and measurements cover a temperature range from room temperature up to 570 K. The technique is applied here in a novel way that eliminates all remaining contact resistances. This allows the apparatus to operate in an absolute way. The method makes use of a soft silicone paste material between the hot wires of the technique and the solid of interest. Measurements of the transient temperature rise of the wires in response to an electrical heating step in the wires over a period of 20 ms up to 20 s allow an absolute determination of the thermal conductivity of the solid, as well as of the silicone paste. The method is based on a full theoretical model with equations solved by a two-dimensional finite-element method applied to the exact geometry. At the 95% confidence level, the standard deviation of the thermal conductivity measurements is 0.1% for Pyrex 7740, 0.4% for Pyroceram 9606, and 0.2% for stainless steel AISI 304L, while the standard uncertainty of the technique is less than 1.5%.