A Simple Model for the Effective Thermal Conductivity of a Particulate Mixture

2002 ◽  
Author(s):  
Mehrdad Massoudi ◽  
Tran X. Phuoc
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Dissipation ◽  
Accurate Estimate ◽  
The Self ◽  
Control Measures ◽  
Heating Process ◽  
Self Heating ◽  
History Of ◽  
Phenomenological Coefficients

When a coal stockpile is stored in the presence of air, slow oxidation of the carbonaceous materials occurs and heat is released. If the rate of heat generation within the stockpile is greater than the rate of heat dissipation and transportation to the external environment, the self-heating of the coal stockpile ensues. The self-heating of coal stockpiles has a long history of posing significant problems to coal producers because it lowers the quality of coal and may result in hazardous thermal runaway. Precise prediction of the self-heating process is, therefore, necessary in order to identify and evaluate control measures and strategies for safe coal mining, storage and transportation. Such a prediction requires an accurate estimate of the various processes associated with the self-heating which are impossible unless the appropriate phenomenological coefficients are known. This note is to present a simple approach to determine the effective thermal conductivity of a granular porous medium such as a coal stockpile.

scholarly journals Ice-Prevention and De-Icing Capacity of Epoxy Resin Filled with Hybrid Carbon-Nanostructured Forms: Self-Heating by Joule Effect

Nanomaterials ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 2427
Author(s):  
Catalina Farcas ◽  
Oscar Galao ◽  
Luigi Vertuccio ◽  
Liberata Guadagno ◽  
M. Dolores Romero-Sánchez ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Aspect Ratio ◽  
Epoxy Resin ◽  
Epoxy Matrix ◽  
Heat Dissipation ◽  
The Self ◽  
Joule Effect ◽  
Self Heating ◽  
Heating Capacity

In this study, CNTs and graphite have been incorporated to provide electrical conductivity and self-heating capacity by Joule effect to an epoxy matrix. Additionally, both types of fillers, with different morphology, surface area and aspect ratio, were simultaneously incorporated (hybrid CNTs and graphite addition) into the same epoxy matrix to evaluate the effect of the self-heating capacity of carbon materials-based resins on de-icing and ice-prevention capacity. The self-heating capacity by Joule effect and the thermal conductivity of the differently filled epoxy resin were evaluated for heating applications at room temperature and at low temperatures for de-icing and ice-prevention applications. The results show that the higher aspect ratio of the CNTs determined the higher electrical conductivity of the epoxy resin compared to that of the epoxy resin filled with graphite, but the 2D morphology of graphite produced the higher thermal conductivity of the filled epoxy resin. The presence of graphite enhanced the thermal stability of the filled epoxy resin, helping avoid its deformation produced by the softening of the epoxy resin (the higher the thermal conductivity, the higher the heat dissipation), but did not contribute to the self-heating by Joule effect. On the other hand, the feasibility of electrically conductive epoxy resins for de-icing and ice-prevention applications by Joule effect was demonstrated.

Numerical modelling of the self-heating process of a wet porous medium

2011 ◽  
Vol 54 (25-26) ◽  
pp. 5200-5206 ◽  
Author(s):  
A. Ejlali ◽  
D.J. Mee ◽  
K. Hooman ◽  
B.B. Beamish
Keyword(s):  
Porous Medium ◽  
Numerical Modelling ◽  
The Self ◽  
Heating Process ◽  
Self Heating

Size Effects on Nonequilibrium Laser Heating of Metal Films

1993 ◽  
Vol 115 (4) ◽  
pp. 842-847 ◽  
Author(s):  
T. Q. Qiu ◽  
C. L. Tien
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Size Effects ◽  
Laser Heating ◽  
Energy Exchange ◽  
Short Pulse ◽  
Heating Process ◽  
Metal Thin Films ◽  
Short Pulse Laser

Picosecond and sub-picosecond lasers have become important tools in the fabrication and study of microstructures. When the laser pulse duration becomes comparable with or less than the characteristic time of energy exchange among microscopic energy carriers, the excited carriers are no longer in thermal equilibrium with the other carriers, creating a nonequilibrium heating situation. The presence of interfaces in metals provides additional scattering processes for electrons, which in turn affects the nonequilibrium heating process. This work studies size effects, due to both surface scattering and grain-boundary scattering, on the thermal conductivity and the energy exchange between electrons and the material lattice. A simple formula is established to predict the influence of film thickness, grain size, interface scattering parameters, and the electron and lattice temperatures on the effective thermal conductivity of metal thin films. Predictions of the analysis agree with the available experimental data. A three-energy-level model is developed to characterize the energy exchange between electrons and the lattice. This study shows that the size effect reduces the effective thermal conductivity and increases the electron-phonon energy exchange rate. The results are useful for improving processing quality, interpreting diagnostic results, and preventing thermal damage of thin films during short-pulse laser heating.

scholarly journals Numerical studies on the heat dissipation process in elastomers under rotating loading direction

2021 ◽  
Author(s):  
M. Abdelmoniem ◽  
B. Yagimli
Keyword(s):  
Heat Dissipation ◽  
Viscoelastic Model ◽  
Material Model ◽  
Fatigue Tests ◽  
Shear Loading ◽  
The Self ◽  
Self Heating ◽  
Applied Loading ◽  
User Subroutine ◽  
Numerical Studies

AbstractElastomeric components such as car bearings and vibration dampers are subjected to dynamic loads with various amplitudes and loading directions during operation. To better understand the lifetime expectancy of these components it is required to implement a material model that sufficiently accounts for the material thermo-mechanical behaviour. This paper implements a finite viscoelastic model which includes heat dissipation and addresses the effect of inelasticity on the self-heating and the applied loading conditions. The material model is implemented in a user subroutine and finite element calculations are carried out on a simple shear loading with rotating directions. The self-heating effect and the resulting variation of the dissipation induced forces are shown and discussed. With the aid of the presented material model, thermo-mechanically coupled simulations can be performed. Based on the results, the required loading limits and boundary conditions for the mechanical fatigue tests can be defined to minimise the thermal fatigue effects.

Improvement in Self-Heating Characteristic by Utilizing Sapphire Substrate in Omega-Gate-Shaped Nanowire Field Effect Transistor for Wearable, Military, and Aerospace Application

2021 ◽  
Vol 21 (5) ◽  
pp. 3092-3098
Author(s):  
Young Suh Song ◽  
Hyunwoo Kim ◽  
Junsu Yu ◽  
Jongho Lee
Keyword(s):  
Computer Aided Design ◽  
Field Effect ◽  
Field Effect Transistor ◽  
Heat Dissipation ◽  
Silicon On Insulator ◽  
The Self ◽  
Self Heating ◽  
Aerospace Applications ◽  
Radiation Resistant ◽  
Effect Transistor

In this study, we propose an omega-shaped-gate nanowire field effect transistor (ONWFET) with a silicon-on-sapphire (SOS) substrate. In order to investigate improvements in the self-heating characteristic with the use of a SOS substrate, the lattice temperature is examined using a Synopsys Sentaurus 3D Technology computer-aided design (TCAD) simulator with the results compared to those with a silicon-on-insulator (SOI) substrate. To validate the proposed structure with the SOS substrate, the locations of hot spots and heat dissipation paths (heat sinks) depending on the substrate materials are also analyzed. The electrical characteristics, specifically the on-current (Ion), off-current (Ioff), and subthreshold swing (SS), were investigated as well. Hence, it is demonstrated here that incorporating a SOS substrate can improve both the self-heating characteristic and the SS at the same time. Therefore, enhanced logic devices are feasible if using an ONWFET with a SOS substrate. Examples include wearable devices and military and future aerospace applications achieved by the radiation-resistant material Al2O3 that has high thermal conductivity.

An Experimental Study of Effective Thermal Conductivity of High Temperature Insulations

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Bo-ming Zhang ◽  
Wei-hua Xie ◽  
Shan-yi Du ◽  
Shu-yuan Zhao
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Maximum Temperature ◽  
Environmental Pressures ◽  
Average Temperature ◽  
Experimental Apparatus ◽  
History Of ◽  
Temperature And Pressure ◽  
Transfer Mechanisms ◽  
Thermal Conductivities

An experimental apparatus was designed and fabricated to measure the effective thermal conductivities and simulate the temperature and pressure history of reentry of a launch vehicle into a planetary atmosphere with a maximum temperature of 1600°C. An improved testing method was used to test the thermal conductivities of an alumina fibrous insulation at environmental pressures from 0.03Pato105Pa with the average temperature of the sample increased to 864°C and its density being 128kg∕m3. A method based on temperature difference is used to compute the in-plane effective thermal conductivity, and the result shows that the in-plane thermal conductivity along the y axis is 1.47 times that along the x axis. The influences of temperature and pressure on the contribution of three heat transfer mechanisms to the effective thermal conductivities were compared.

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