scholarly journals Closure to “Discussions of ‘High Temperature Thermal Conductivity of Rare Gases and Gas Mixtures’” (1968, ASME J. Heat Transfer, 90, p. 324–326)

1968 ◽  
Vol 90 (3) ◽  
pp. 326-327
Author(s):  
Richard A. Matula
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
High Temperature ◽  
Gas Mixtures ◽  
Rare Gases

scholarly journals A NOTE ON THE CONSTANT THERMAL CONDUCTIVITY HYPOTHESIS AND ITS CONSEQUENCE FOR CONDUCTION HEAT TRANSFER PROBLEMS

2014 ◽  
Vol 13 (2) ◽  
pp. 48
Author(s):  
R. M. S. Gama
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
High Temperature ◽  
Heat Generation ◽  
Strong Dependence ◽  
Temperature Gradients ◽  
Conduction Heat Transfer ◽  
Kirchhoff Transformation ◽  
Constant Thermal Conductivity ◽  
Transfer Problems

This work discuss the usual constant conductivity assumption and its consequences when a given material presents a strong dependence between the temperature and the thermal conductivity. The discussion is carried out considering a sphere of silicon with a given heat generation concentrated in a vicinity of its centre, giving rise to high temperature gradients. This particular case is enough to show that the constant thermal conductivity hypothesis may give rise to very large errors and must be avoided. In order to surpass the mathematical complexity, the Kirchhoff transformation is used for constructing the solution of the problem. In addition, an equation correlating thermal conductivity and the temperature is proposed.

Fabrication of PMIA/fBN Dielectric Composite with Enhanced Breakdown Strength and Thermal Conductivity

2019 ◽  
Vol 960 ◽  
pp. 256-262
Author(s):  
Guang Yu Duan ◽  
Zu Ming Hu
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
High Temperature ◽  
Dielectric Property ◽  
Dielectric Loss ◽  
Breakdown Strength ◽  
Dielectric Composite ◽  
Novel Method ◽  
Thermal Conductivities

A high-temperature poly (m-phenyleneisophthalamide) (PMIA) dielectric composite was successfully manufactured with functionalized BN (fBN) fillers. Due to effective modification by KH-550, fBN particles evenly dispersed in PMIA matrix. The dielectric property, breakdown strength and thermal conductivity of PMIA/fBN dielectric composite were researched. The consequences indicate that fBN fillers can not only decrease the dielectric loss but also enhance the breakdown strength of PMIA/fBN dielectric composites. Furthermore, owing to the generated heat transfer pathways by fBN particles, the thermal conductivities improved from 0.23 W·m-1·K-1 of fBN-0 to 0.86 W·m-1·K-1 of fBN-30, demonstrating a significant improvement. These results present a novel method for fabricating high-temperature PMIA/fBN dielectric composites with improved breakdown strength and thermal conductivity.

scholarly journals Characteristics of supercritical heat transfer during filmboiling of nanofluids on a vertical heated wall

2018 ◽  
pp. 29-35
Author(s):  
А. Avramenko ◽  
M. Kovetskaya ◽  
A. Tyrinov ◽  
Yu. Kovetska
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mathematical Model ◽  
Mass Transfer ◽  
Heat Flux ◽  
High Temperature ◽  
Heat And Mass Transfer ◽  
Heated Surface ◽  
Heated Wall ◽  
Film Boiling

Nanofluid using for intensification of heat transfer during boiling are analyzed. The using boiling nanofluids for cooling high-temperature surfaces allows significantly intensify heat transfer process by increasing the heat transfer coefficient of a nanofluid in comparison with a pure liquid. The properties of nanoparticles, their concentration in the liquid, the underheating of the liquid to the saturation temperature have significant effect on the rate of heat transfer during boiling of the nanofluid. Increasing critical heat flux during boiling of nanofluids is associated with the formation of deposition layer of nanoparticles on heated surface, which contributes changing in the microcharacteristics of heat exchange surface. An increase in the critical heat flux during boiling of nanofluids is associated with the formation of a layer of deposition of nanoparticles on the surface, which contributes to a change in the microcharacteristics of the heat transfer of the surface. Mathematical model and results of calculation of film boiling characteristics of nanofluid on vertical heated wall are presented. It is shown that the greatest influence on the processes of heat and mass transfer during film boiling of the nanofluid is exerted by wall overheating, the ratio of temperature and Brownian diffusion and the concentration of nanoparticles in the liquid. The mathematical model does not take into account the effect changing structure of the heated surface on heat transfer processes but it allows to evaluate the effect of various thermophysical parameters on intensity of deposition of nanoparticles on heated wall. The obtained results allow to evaluate the effect of nanofluid physical properties on heat and mass transfer at cooling of high-temperature surfaces. The using nanofluids as cooling liquids for heat transfer equipment in the regime of supercritical heat transfer promotes an increase in heat transfer and accelerates the cooling process of high-temperature surfaces. Because of low thermal conductivity of vapor in comparison with the thermal conductivity of the liquid, an increase in the concentration of nanoparticles in the vapor contributes to greater growth in heat transfer in the case of supercritical heat transfer.

Modeling of wave configuration during electrically ignited combustion synthesis

2001 ◽  
Vol 16 (1) ◽  
pp. 93-100 ◽  
Author(s):  
O. A. Graeve ◽  
E. M. Carrillo-Heian ◽  
A. Feng ◽  
Z. A. Munir
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
High Temperature ◽  
Combustion Synthesis ◽  
Small Samples ◽  
Combustion Mode ◽  
Temperature Synthesis ◽  
Ignition Point ◽  
High Temperature Synthesis ◽  
Material Systems

A model was developed to study the process of current-ignited combustion synthesis. In this process, Joule heating raises the temperature to the ignition point, at which the sample reacts to form a product. Two material systems were modeled: the synthesis of SiC and MoSi2. It was found that the mode of combustion is a function of the size (radius) of the sample. The anticipated volume combustion mode was only evident in small samples. At higher values of the radius, the mode becomes wavelike (selfpropagating high-temperature synthesis) in nature. The transition from volume to wave combustion mode also depended on the properties of the material. The results are interpreted in terms of thermal conductivity and heat-transfer conditions.

High Temperature Thermal Conductivity of Rare Gases and Gas Mixtures

1968 ◽  
Vol 90 (3) ◽  
pp. 319-324 ◽  
Author(s):  
Richard A. Matula
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Shock Tube ◽  
Voltage Drop ◽  
Gas Mixtures ◽  
Reflected Shock Wave ◽  
Reflected Shock ◽  
Least Squares Fit ◽  
Theoretical Predictions ◽  
Relationship Of

The thermal conductivities of pure argon, pure xenon, and of three helium-argon mixtures have been determined in the temperature range 650–5000 deg K by measuring heat transfer rates from shock heated gases to the end wall of a shock tube. The heat transfer rate was measured by monitoring the time dependence of the voltage drop across a thin-film gage mounted in the end cap of the shock tube. During the course of the experiments, the pressure of the test gas behind the reflected shock wave ranged from approximately 1/3 to 2 atmospheres. In all cases, the temperature dependence (T) of the thermal conductivity (K) was assumed to follow a power law relationship of the form K/Kw = (T/Tw)b where Kw is the established value of the gas conductivity at the reference temperature (Tw) which was chosen near room temperature. The parameter b was evaluated by applying a least squares fit to the experimental data. Theoretical values of the conductivity of all of the gases studied were computed utilizing the Lennard-Jones (6–12) potential. In the case of the gas mixtures, an empirical combining rule was used to relate the force constants between unlike atoms to the known constants between like atoms. The experimental and theoretical results for the pure gases are in good agreement. The experimental and theoretical values of the mixture conductivities are within 10–20 percent, and as expected the theoretical predictions are least accurate for equimolar mixtures.

scholarly journals Influence of Material Coating on the Heat Transfer in a Layered Cu-SiC-Cu Systems

2017 ◽  
Vol 62 (2) ◽  
pp. 1311-1314
Author(s):  
A. Strojny-Nędza ◽  
K. Pietrzak ◽  
M. Teodorczyk ◽  
M. Basista ◽  
W. Węglewski ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Silicon Carbide ◽  
Thermal Properties ◽  
High Temperature ◽  
Vapour Deposition ◽  
Chemical Vapour ◽  
Plasma Sintering ◽  
Metal Ceramic ◽  
Spark Plasma

AbstractThis paper describes the process of obtaining Cu-SiC-Cu systems by way of spark plasma sintering. A monocrystalline form of silicon carbide (6H-SiC type) was applied in the experiment. Additionally, silicon carbide samples were covered with a layer of tungsten and molybdenum using chemical vapour deposition (CVD) technique. Microstructural examinations and thermal properties measurements were performed. A special attention was put to the metal-ceramic interface. During annealing at a high temperature, copper reacts with silicon carbide. To prevent the decomposition of silicon carbide two types of coating (tungsten and molybdenum) were applied. The effect of covering SiC with the aforementioned elements on the composite’s thermal conductivity was analyzed. Results were compared with the numerical modelling of heat transfer in Cu-SiC-Cu systems. Certain possible reasons behind differences in measurements and modelling results were discussed.

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