Determination Of Thermal Conductivity Coefficient Research Articles

Diagnostics of a Domestic Hot Water Storage Tank under Operating Conditions

This paper presents a new method for the diagnostics of a hot water storage tank under operating conditions. Depending on the operating point of the tank, the method enables determination of thermal conductivity coefficients of the coil heat exchanger, which allows us to determine the intensity of heat transfer between the transfer medium and water in the tank as well as of tank walls, which consequently enables determination of heat losses to the environment. Furthermore, the dynamic properties of the tank may also be determined by applying this method. The advantage of this method is possibility of analyzing changes in the material constants of the coil heat exchanger, tank walls, and dynamic properties of the tank as a function of mass flow of the medium supplying the coil heat exchanger. The possibility of determining coefficients of thermal conductivity as well as the inertia of tank and exchanger, based on temperature measurements acquired in operating conditions is a novelty in this paper. Knowing the variability of material constants and of dynamic properties of the tank as a function of medium flow rate allows multicriteria optimization to be performed which, with a conventional design of the tank, results in a reduction of up to 10% in the time taken to prepare domestic hot water.

Dynamic Thermal Properties Estimation Using Sensitivity Coefficients for Rapid Heating Process.

Thermal conductivity determination of food at temperatures > 100 °C still remains a challenge. The objective of this study was to determine the temperature-dependent thermal conductivity of food using rapid heating (TPCell). The experiments were designed based on scaled sensitivity coefficient (SSC), and the estimated thermal conductivity of potato puree was compared between the constant temperature heating at 121.10 °C (R12B10T1) and the rapid heating (R22B10T1). Temperature-dependent thermal conductivity models along with a constant conductivity were used for estimation. R22B10T1 experiment using the k model provided reliable measurements as compared to R12B10T1 with thermal conductivity values from 0.463 ± 0.011 W m−1 K−1 to 0.450 ± 0.016 W m−1 K−1 for 25–140 °C and root mean squares error (RMSE) of 1.441. In the R12B10T1 experiment, the analysis showed the correlation of residuals, which made the estimation less reliable. The thermal conductivity values were in the range of 0.444 ± 0.012 W m−1 K−1 to 0.510 ± 0.034 W m−1 K−1 for 20–120 °C estimated using the k model. Temperature-dependent models (linear and k models) provided a better estimate than the single parameter thermal conductivity determination with low RMSE for both types of experiments. SSC can provide insight in designing dynamic experiments for the determination of thermal conductivity coefficient.

Calculation of thermal conductivity coefficient of thermal insulation mixtures

The majority of prospective deposits of oil and natural gas in the Russian Federation are located in the zones of permanently frozen rocks - the permafrost. This region is characterized not only by harsh climatic conditions, causing difficulty in development of the deposits, but also by negative cryogenic processes impacting the reliability of construction and use of various engineering structures. It is necessary to know the regularities of and to be able to forecast the thermal regime of the soils and rocks in order to forecast the degree of influence of cryogenic processes on the engineering structures. In particular, the depth of thawing and freezing of soils in the locations of underground and surface structures, such as pipelines, is of importance. The depth of thawing of soil is an important indicator for the choice of the method of construction on the frozen surfaces. Control of the thawing/freezing depth can be ensured with the use of thermal insulation as well as replacement of the soil itself with an artificial soil with preselected properties. Transportation of oil and natural gas is realized using pipelines laid through frozen rocks. In order to decrease cryogenic impact on the pipes, special thermal insulation beddings replacing a section of soil are used. To determine the thermal insulation properties of beddings made out of polystyrene, variant calculations of thermal conductivity coefficient have been done according to the Odelevski and Schwerdtfeger formulas. Calculations were done for beddings in thawed and frozen state with different polystyrene content concentration. The conclusion is that both formulas can be used for theoretical determination of thermal conductivity coefficient. Absolute and relative errors do not exceed those permissible in engineering calculations for a wide range of conditions.

Results of determination of thermal conductivity coefficient for board materials from plant waste

This paper solves the problem of recycling irretrievable waste spinning flax and cotton. This plant waste is incinerated or sent to landfill. It is proposed to use plant waste as a filler for building materials for thermal insulation purposes. New thermal insulating materials based on plant waste are manufactured using the technology of soft fibreboard wet production method. Synthetic thermosetting or inorganic binders are used as the matrix of the composites. The article presents the results of an experimental determination of the coefficient of thermal conductivity of plate materials from irretrievable spinning waste of flax and cotton fibers. Composites based on flax waste filler have a lower value of thermal conductivity coefficient than for cotton waste plates. The results of determining the thermal conductivity coefficient of composite boards based on spinning flax and cotton showed that the developed material can be used as an internal thermal insulating layer of enclosing structures.

Determination of Thermal Conductivity Coefficient of Moist Sodium Carboxymethyl Cellulose

The heat exchange process of moist sodium carboxymethyl cellulose is studied. The method for determining the thermal conductivity coefficient of a moist disperse material is developed. The thermophysical properties of sodium carboxymethyl cellulose are determined. The influence of moisture content and density of the material on its thermal conductivity coefficient is studied. An empirical equation is derived by processing the experimental data to calculate the thermal conductivity coefficient of sodium carboxymethyl cellulose at different densities of the moist material.

Determination of thermal conductivity coefficient by Green-Kubo formula using the minimum image method

Determination of thermal conductivity coefficient by Green-Kubo formula using the minimum image method

Analysis of Specificity of ecological insulation material thermal Parameters

This paper is devoted to analysis of insulation materials quality and characteristics, method for the determination of thermal conductivity coefficient and the influence of various factors on the thermal conductivity coefficient. The paper summarizes the estimated process consumption of thermal energy. The research is defined experimental hemp fiber-sheaves insulation plates manufactured in Latvia further specified actual parameter and quality water absorption; thickness changes; drying process; thermal conductivity coefficient; thermal conductivity coefficient depending from moisture. Research is made using experimental hemp fiber-sheaves insulation pattern manufactured in Latvia – plates in size 300 x 300 mm. In research totally are used three hemp fiber-sheaves pattern series with different substance and extrusion modes. Each series consist from four plate with different thickness. As result of research is determined hemp fiber-sheaves insulation pattern Water absorption, dynamics of Drying process, Thickness changes, Thermal conductivity coefficient and Thermal conductivity coefficient depending from moisture.

Determination of thermal conductivity coefficient of crystals with the garnet structure at high temperatures

At high temperatures, the simple expression for thermal conductivity of crystals with the garnet structure is obtained, which allows one to determine this quantity if the lattice constant or density of these crystals is known. The thermal conductivity coefficients for the garnet crystals of different compositions calculated from the obtained formula are in a good agreement with the experimentally measured values.

Contribution to the Methodology of the Determination of the Thermal Conductivity Coefficients Λ of Materials Applied in the Railway Subbase Structure

The paper focuses on the methodology of determination of thermal conductivity coefficients λ of the construction materials of railway subbase. The determination of the thermal conductivity coefficients λ depends on the determination of the specific heat capacity and the time interval as sub-parameters. The paper presents specialized equipment for the determination of these parameters, the stated procedures and the method of test evaluation.The paper focuses on the presentation of the results of the experimental determination of the thermal conductivity coefficients λ of selected construction materials (clay, track ballast, fraction 32/63 mm, crushed aggregate fraction 0/32 mm and sandy gravel 0/32 mm). In the conclusion there is the confrontation of the values of the thermal conductivity coefficients λ stated by the experimental laboratory measurements with the values stated in TNZ 73 6312 and STN EN ISO 10 456.

Thermal conductivity of rocks and its variation with uniaxial and triaxial stress

One of the prime tasks of a mining engineer is to calculate the mine cooling load necessary for mine air conditioning system, which must provide suitable working conditions for the work force primarily at the working faces. Additionally the determination of thermal parameters of rocks plays an important role in the activities of geothermal energy production, energy storage and radioactive waste disposal. These activities require the determination of thermal conductivity coefficient of rocks especially around underground openings. This paper deals with the results of the variation of thermal conductivity of rocks with uniaxial and triaxial stress at the laboratory scale. In this way, it is possible to see the difference between thermal conductivity coefficient values under uniaxial and triaxial stress and to draw the conclusions necessary to be taken into consideration for heat flow calculations. To this end, rock specimens have been tested via a new device developed by authors. The results obtained from the tests performed with this device, as given in the related plots, show that the thermal conductivity coefficients determined are suitable for use to support design analyses.

Rapid methods for determination of thermal conductivity coefficients of thermoelectric meaterials in semiconductor thermobatteries

Methods are developed for absolute and relative determination of the thermal conductivity coefficient of specimens of semiconductor material, with the only measurements required being determination of the relative temperature heads between the external medium and the specimen faces when controlled heat exchange is created at the external surface.

The determination of thermal conductivity coefficients of liquids by a thermal lens technique

The thermal lens technique, already established for gases, is extended to the measurements of liquid-phase thermal conductivity coefficients, the best values obtained at 300±2 K being 0.59, 0.171, 0.116, 0.149 and 0.110 W m−1 K−1 for water, acetone, chloroform, butan-2-one and chlorobenzene respectively. It is also shown that the accuracy of measurement of the curvature of the axial-pulsed-laser beam intensity, with an array of resolution equal to the pinhole diameter, is not sufficient to give the precision of measurement associated with a calibration approach.