scholarly journals Determination of the Radiation Exchange Factor in the Bundle of Steel Round Bars

Energies ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5263 ◽  
Author(s):  
Rafał Wyczółkowski ◽  
Marek Gała ◽  
Stanisław Szwaja ◽  
Andrzej Piotrowski
Keyword(s):  
Thermal Conductivity ◽  
Geometric Model ◽  
Initial Point ◽  
Temperature Range ◽  
Exchange Factor ◽  
Radiation Exchange ◽  
The Difference ◽  
Radiative Thermal Conductivity ◽  
Bar Diameter

A method to obtain a radiation exchange factor FR in the bundle of steel round bars is presented. This parameter is required for determination of the radiative thermal conductivity krd, which is one of the basic thermal properties of the bar bundles. In the presented approach, the analyzed parameter is calculated indirectly. The initial point for calculations is the geometric model of the medium defined as a unit cell. Then, for the elements present in this cell, the thermal resistance of both conduction and radiation is determined. The radiation resistance is calculated from the radiosity balance of the surfaces enclosing the analyzed system. On this basis, the radiation thermal conductivity krd is calculated. Next, taking into account the bar diameter, the value of parameter FR is also determined. The analysis is performed at the process temperature range of 200 to 800 °C for three bar diameters: 10, 20 and 30 mm, and for the three porosities of the bundle. Different emissivity of bars in the range of 0.5 to 0.9 was also taken into account. Finally, a relationship that allows calculating the FR factor correlated with the emissivity of the bars and the bundle porosity was established. The krd obtained from the methodology presented and compared with the values calculated directly do not exceed 9%; however, after averaging over the entire temperature range of the process, the difference does not exceed 0.2%.

Determination of the thermal conductivity of polypyrrole over the temperature range 280–335 K

1993 ◽  
Vol 28 (18) ◽  
pp. 5092-5098 ◽  
Author(s):  
B. A. Lunn ◽  
J. Unsworth ◽  
N. G. Booth ◽  
P. C. Innis
Keyword(s):  
Thermal Conductivity ◽  
Temperature Range

scholarly journals THERMOPHYSICAL PROPERTIES OF ALLOY COMPOSITIONS (2Bi2O3∙B2O3)100-x(2Bi2O3∙3GeO2)x (x=0, 10, 50)

2021 ◽  
pp. 44-48
Author(s):  
S.I. Bananyarli ◽  
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Phase Transitions ◽  
Thermal Resistance ◽  
Temperature Dependence ◽  
Thermophysical Properties ◽  
Chemical Bonds ◽  
Temperature Range ◽  
The Difference

The termophisical properties, namely, the temperature dependence of thermal conductivity, thermal resistance and heat capacity of the allays compositions (2Bi2O3∙B2O3)100-x (2Bi2O3∙3GeO2)x in the (300–600) K temperature range have ligated been invest. An increase in thermal conductivity χ(T) above 500 K is probably associated with the softening of alloys and the presence of blurred phase transitions, which are accompanied by partial breaking of chemical bonds. It was revealed that the heat capacity in alloys of the compositions (2Bi2O3∙B2O3)100-x (2Bi2O3∙3GeO2)x increases with an increase in the GeO2 concentration. In the studied samples, that showed their own disorder during solidification, the thermal conductivity is strongly reduced due to the enhancement of the anharmonicity of phonon – phonon interactions. İn turn a small "disorder" introduced by defects due to the difference in masses is not noticeable against the background of the huge "disorder" inherent in oxide substances

High Temperature Thermal Conductivity Measurements of Quasicrystalline Al70.8Pd20.9Mn8.3

2000 ◽  
Vol 626 ◽  
Author(s):  
Philip S. Davis ◽  
Peter A. Barnes ◽  
Cronin B. Vining ◽  
Amy L. Pope ◽  
Robert Schneidmiller ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
High Temperature ◽  
Radiative Heat ◽  
Accurate Determination ◽  
Fourth Power ◽  
Radiative Effects ◽  
Radiative Heat Loss ◽  
3Ω Method ◽  
Temperature Range

ABSTRACTWe report measurements of the thermal conductivity on a potential high temperature thermoelectric material, the quasicrystal Al70.8Pd20.9Mn8.3. Thermal conductivity is determined over a temperature range from 30 K to 600 K, using both the steady state gradient method and the 3ω method. Measurements of high temperature thermal conductivity are extremely difficult using standard heat conduction techniques. These difficulties arise from the fact that heat is lost due to radiative effects. The radiative effects are proportional to the temperature of the sample to the fourth power and therefore can lead to large errors in the measured thermal conductivity of the sample, becoming more serious as the temperature increases. For thermoelectric applications in the high temperature regime, the thermal conductivity is an extremely important parameter to determine. The 3ω technique minimizes radiative heat loss terms, which will allow for more accurate determination of the thermal conductivity of Al70.8Pd20.9Mn8.3 at high temperatures. The results obtained using the 3ω method are compared to results from a standard bulk-thermal-conductivity-technique on the same samples over the temperature range, 30 K to 300 K.

Determination of Thermal Conductivity of Biomaterials in the Temperature Range 233–313K Using a Tiny Detector Made of a Self-Heated Thermistor

2002 ◽  
Vol 1 (2) ◽  
pp. 141-147 ◽  
Author(s):  
Haifeng Zhang ◽  
Shuxia Cheng ◽  
Liqun He ◽  
Aili Zhang ◽  
Ying Zheng ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Temperature Range

scholarly journals Thermal Conductivity of Frozen Sediments Containing Self-Preserved Pore Gas Hydrates at Atmospheric Pressure: An Experimental Study

Geosciences ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 65 ◽  
Author(s):  
Evgeny Chuvilin ◽  
Boris Bukhanov
Keyword(s):  
Thermal Conductivity ◽  
Physical Properties ◽  
Gas Hydrates ◽  
Atmospheric Pressure ◽  
The Self ◽  
Needle Probe ◽  
Hydrate Saturation ◽  
The Difference ◽  
Hydrate Bearing Sediments

The paper presents the results of an experimental thermal conductivity study of frozen artificial and natural gas hydrate-bearing sediments at atmospheric pressure (0.1 MPa). Samples of hydrate-saturated sediments are highly stable and suitable for the determination of their physical properties, including thermal conductivity, due to the self-preservation of pore methane hydrate at negative temperatures. It is suggested to measure the thermal conductivity of frozen sediments containing self-preserved pore hydrates by a KD-2 needle probe which causes very little thermal impact on the samples. As shown by the special measurements of reference materials with known thermal conductivities, the values measured with the KD-2 probe are up to 20% underestimated and require the respective correction. Frozen hydrate-bearing sediments differ markedly in thermal conductivity from reference frozen samples of the same composition but free from pore hydrate. The difference depends on the physical properties of the sediments and on changes in their texture and structure associated with the self-preservation effect. Namely, it increases proportionally to the volumetric hydrate content, hydrate saturation, and the percentage of water converted to hydrate. Thermal conductivity is anisotropic in core samples of naturally frozen sediments that enclose visible ice-hydrate lenses and varies with the direction of measurements with respect to the lenses. Thermal conductivity measurements with the suggested method provide a reliable tool for detection of stable and relict gas hydrates in permafrost.

Optical Determination of Thermal Conductivity with a Plane Source Technique

1968 ◽  
Vol 23 (5) ◽  
pp. 682-686 ◽  
Author(s):  
Silas E. Gustafsson ◽  
Nils-Olov Halling ◽  
Rolf A. E. Kjellander
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Temperature Dependence ◽  
Theoretical Approach ◽  
Experimental Results ◽  
Plane Source ◽  
Melting Points ◽  
Temperature Range ◽  
Optical Determination

The thermal conductivity and the thermal diffusivity of the three alkali nitrates LiNO3 , RbNO3 and CsNO3 have been measured over a temperature range between 50° and 100 °C above their melting points. Any temperature dependence of the thermal conductivity cannot be established for any of the investigated liquids but the results indicate that it must be less than 10-3 °C-1. The experimental results are compared with the conductivities which can be calculated with already excisting theories. A somewhat modified theoretical approach is suggested for estimating the thermal conductivity, where no adjustable parameters are being used. The experimental and theoretical values at the melting points agree within about 10 percent.

scholarly journals Determination of Radiative Thermal Conductivity in Needlepunched Nonwovens

2008 ◽  
Vol 3 (4) ◽  
pp. 155892500800300 ◽  
Author(s):  
Rahul Vallabh ◽  
Pamela Banks-Lee ◽  
Massoud Mohammadi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Extinction Coefficient ◽  
Dominant Mode ◽  
Hot Plate ◽  
Guarded Hot Plate ◽  
Ftir Spectrometer ◽  
Radiative Thermal Conductivity

Radiation heat transfer is found to be the dominant mode of heat transfer at temperatures higher than 400–500K [11]. Convection heat transfer being negligible in nonwovens, effective thermal conductivity is given by the sum of its conduction and radiation components. In this research two methods were identified to determine radiative thermal conductivity of needlepunched samples made from Nomex fibers. The first method involved the determination of radiative thermal conductivity using effective (total) thermal conductivity determined using a Guarded Hot Plate (GHP) instrument. In the second method radiative thermal conductivity was estimated using the extinction coefficient of samples. The extinction coefficient was determined by using direct transmission measurements made using a Fourier Transform InfraRed (FTIR) spectrometer. Results confirmed that radiation was the dominant mode of heat transfer at temperatures higher than 535 K. The conduction component of effective thermal conductivity did not change much in the range of densities tested. Empirical models for predicting the temperature difference across thickness of the fabric and the radiative thermal conductivity with R-square values of 0.94 and 0.88 respectively showed that fabric density, fabric thickness, fiber fineness, fiber length, mean pore size and applied temperature were found to have significant effect on the effective thermal conductivity and its radiation component. Though a high correlation between the results of Method 1 (Guarded Hot Plate) and Method 2 (FTIR) was not seen, the absorbance measurements made using the FTIR spectrometer were found to have significant effect on the radiative thermal conductivity.

Identifizierung der Zementart in hydratisierten Betonen und Mörteln / Identification of the Type of Cement in Hardened Concretes and Mortars

2000 ◽  
Vol 6 (2) ◽  
pp. 191-218
Author(s):  
F. Splittgerber ◽  
A. Müller
Keyword(s):  
Compressive Strength ◽  
Calcium Oxide ◽  
Cement Paste ◽  
Hardened Concrete ◽  
Portland Cements ◽  
Free Lime ◽  
Temperature Range ◽  
Mineral Phases ◽  
The Difference

Abstract Subject of this paper is the development of a method for the identification of the type of cement present in a hardened concrete or mortar. The method is based on the dehydration of the cement paste and the identification of the phases present after the dehydration. Considering clinker phases and real cements, the following possibilities for the identification of cements were worked out: • differentiation between Portland cements and cements containing additions by the identification of the mineral phases which are typical for the type of the addition • differentiation between ordinary and sulphate resistant Portland cements by the identification of the Ye'elimite phase after a dehydration at a temperature of 1100° C • determination of the characteristic compressive strength of Portland cements by the evaluation of the Alite-content. For an identification at least two dehydration temperatures have to be considered. The first temperature range is at about 1100 to 1200°C. It is important for the identification of the aluminates and ferrites. Temperatures from about 1400 to 1450°C are needed for the dehydration of the silicates. Because of the appearence of melting phases at temperatures above 1200°C, the Alite-content will be determined indirectly by the determination of the Belite-content and the content of free lime after a dehydration at 1100°C. At this temperature the free lime is considered to represent the difference in calcium oxide between the Alite and the Belite.

scholarly journals The effect of temperature on the viscosity of air

1926 ◽  
Vol 113 (763) ◽  
pp. 233-237 ◽  
Keyword(s):  
Present Author ◽  
Effect Of Temperature ◽  
Appreciable Change ◽  
Temperature Range ◽  
Higher Temperature ◽  
The Difference ◽  
Experimental Values ◽  
Coefficient Of Viscosity ◽  
Slight Alteration

In a recent paper Prof. A. 0. Rankine has put forward a number of criticisms of the results obtained from, and the experimental method employed in, the determination of the temperature coefficient of viscosity of air by the present author. In the first place, a comparison is drawn between the author’s results and those of other observers in the lower part of the temperature range, and the conclusion is drawn therefrom that there is a possibility of an error of 3 percent, in the author’s measurements throughout the whole range of temperature used. This inference is reached from the figures quoted in Table II of Rankine’s paper, in which the temperature range from 15° to 183° C. is considered. That some difference exists between the author’s results and those of other observers in the lower part of the temperature range is clear, but it must again be emphasised that the values given for low temperatures are not experimental values, but were obtained by an extension of the graph (fig. 2) for higher temperature measurements to the value of the viscosity as given by Millikanj for room temperatures. A slight alteration of the curvature of this extension would make an appreciable change in the ratios η100/η15 and η183/η15 , but this would not be sufficient to account for the curvature at B in fig. 3 of the original paper. If the values of T ⅜ /η for Breitenbach’s results at 182° C. and 302° C. are plotted on this curve, they lie above the present results and on a curve which would intersect AB at about 600° C. That part of the difference is due to this cause seems to be indicated by the fact that the difference diminishes as the temperature rises. Thus at 300° C. the following values of η300/η15 are obtained by Breitenbach, the only other worker at this temperature, and the author. The figures used are those given by Rankine.

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