How the coarse fraction influences the microstructure and the effective thermal conductivity of alumina castables – An experimental and numerical study

2018 ◽  
Vol 38 (1) ◽  
pp. 303-312 ◽  
Author(s):  
Jens Fruhstorfer ◽  
Cornelius Demuth ◽  
Pitt Goetze ◽  
Christos G. Aneziris ◽  
Subhashis Ray ◽  
...  
2016 ◽  
Vol 846 ◽  
pp. 500-505
Author(s):  
Wei Jing Dai ◽  
Yi Xiang Gan ◽  
Dorian Hanaor

Effective thermal conductivity is an important property of granular materials in engineering applications and industrial processes, including the blending and mixing of powders, sintering of ceramics and refractory metals, and electrochemical interactions in fuel cells and Li-ion batteries. The thermo-mechanical properties of granular materials with macroscopic particle sizes (above 1 mm) have been investigated experimentally and theoretically, but knowledge remains limited for materials consisting of micro/nanosized grains. In this work we study the effective thermal conductivity of micro/nanopowders under varying conditions of mechanical stress and gas pressure via the discrete thermal resistance method. In this proposed method, a unit cell of contact structure is regarded as one thermal resistor. Thermal transport between two contacting particles and through the gas phase (including conduction in the gas phase and heat transfer of solid-gas interfaces) are the main mechanisms. Due to the small size of particles, the gas phase is limited to a small volume and a simplified gas heat transfer model is applied considering the Knudsen number. During loading, changes in the gas volume and the contact area between particles are simulated by the finite element method. The thermal resistance of one contact unit is calculated through the combination of the heat transfer mechanisms. A simplified relationship between effective thermal conductivity and loading pressure can be obtained by integrating the contact units of the compacted powders.


Author(s):  
Kevin Irick ◽  
Nima Fathi

The evaluation of effective material properties in heterogeneous materials (e.g., composites or multicomponent structures) has direct relevance to a vast number of applications, including nuclear fuel assembly, electronic packaging, municipal solid waste, and others. The work described in this paper is devoted to the numerical verification assessment of the thermal behavior of porous materials obtained from thermal modeling and simulation. Two-dimensional, steady state analyses were conducted on unit cell nano-porous media models using the finite element method (FEM). The effective thermal conductivity of the structures was examined, encompassing a range of porosity. The geometries of the models were generated based on ordered cylindrical pores in six different porosities. The dimensionless effective thermal conductivity was compared in all simulated cases. In this investigation, the method of manufactured solutions (MMS) was used to perform code verification, and the grid convergence index (GCI) is employed to estimate discretization uncertainty (solution verification). The system response quantity (SRQ) under investigation is the dimensionless effective thermal conductivity across the unit cell. Code verification concludes an approximately second order accurate solver. It was found that the introduction of porosity to the material reduces effective thermal conductivity, as anticipated. This approach can be readily generalized to study a wide variety of porous solids from nano-structured materials to geological structures.


2020 ◽  
pp. 109963622093353
Author(s):  
Rongnan Yuan ◽  
Shouxiang Lu

Effective thermal conductivity is an essential parameter to investigate thermal properties of metallic honeycomb sandwich structures. And it cannot be measured by traditional methods due to sandwich structure imbedded with air. A practical experimental equipment was designed to evaluate the value under different temperature from 100°C to 400°C. And it was found that the value of effective thermal conductivity can also be calculated by knowing the thermal conductivity of the reference, thickness of the reference and the slope and intercept of temperature in different layers. Meanwhile, numerical simulation was conducted and the results agreed well with that achieved by experiment. Also, the value of effective thermal conductivity calculated by experiment is close to the value calculated by Swann-Pittman empirical equation. And the method is not limited in metallic honeycomb sandwich structure while it can be applied in most structures with amounts of air. On that basis, heat transfer process of the structure is discussed including heat conduction, heat convection and heat radiation.


Author(s):  
Ich-Long Ngo ◽  
Chan Byon

Augmenting the thermal conductivity of polymer materials is actively being attempted by adding one or more fillers with higher thermal conductivity into matrix materials. In this study, the effective thermal conductivity of composite materials was investigated numerically under the effects of the thermal conductivity ratio between two particle fillers and the matrix material, and the particle volume fractions. The results indicate that the effective thermal conductivity of composites containing hybrid filler is higher than that of single filler. The effective thermal conductivity increases with the increase of thermal conductivity ratio between two fillers in general when this ratio is less than unity, and the maximum effective thermal conductivity approaches when this ratio is less than and close to unity. However, this trend is changed when this ratio is greater than unity. Based on the results, a generalized correlation is proposed as a function of four non-dimensional parameters. The results obtained in this study can be widely utilized for predicting the thermal conductivity of hybrid-filler-nanoparticle composite materials.


2011 ◽  
Vol 45 (23) ◽  
pp. 2465-2473 ◽  
Author(s):  
Qin Zhang ◽  
Zhihua Pi ◽  
Mingxiang Chen ◽  
Xiaobing Luo ◽  
Ling Xu ◽  
...  

The effective thermal conductivity of silicone/phosphor composites is studied experimentally and numerically. Thermal conductivity measurements are conducted from 30°C to 150°C for the composites with phosphor volume fraction up to 40%. In the numerical study, a finite element model with empirical particle size distribution and random particle position is constructed using a probability density function and the Monte Carlo method, and the interfacial thermal resistance layer between phases also introduced in the model. The results indicate that when phosphor concentration is below 25 vol.%, the conductivity of the composite increases slightly with either phosphor volume fraction or temperature, and the Kapitza radius of the composite is 0.8 µm. When phosphor concentration is above 25 vol.%, the increase of conductivity correlates positively with phosphor volume fraction significantly but negatively with the temperature, and the Kapitza radius is 0.032 µm.


2012 ◽  
Vol 33 (8) ◽  
pp. 732-747 ◽  
Author(s):  
Shibin Tang ◽  
Chun’an Tang ◽  
Zhengzhao Liang ◽  
Yongbin Zhang ◽  
Lianchong Li

2017 ◽  
Vol 153 ◽  
pp. 55-68 ◽  
Author(s):  
Lei Shen ◽  
Qingwen Ren ◽  
Linfei Zhang ◽  
Yan Han ◽  
Gianluca Cusatis

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Chuan-Yong Zhu ◽  
Zeng-Yao Li ◽  
Wen-Quan Tao

This paper presents a theoretical and numerical study on the heat conduction of gas confined in a cuboid nanopore, in which there exists a temperature difference between the top and bottom walls and the side walls are adiabatic. A modified gas mean free path in confined space is proposed by considering the impact of collisions between molecules and solid surfaces, with which an effective thermal conductivity model of gas in the transition regime is derived. A direct simulation Monte Carlo (DSMC) study on the heat conduction of argon and helium in a cuboid nanopore is carried out to validate the present model. The influences of the Knudsen number and the treatments of boundary conditions on the heat conduction and effective thermal conductivity of gas in nanopores are studied. The temperature jumps and the reduction of heat flux near side walls are analyzed.


Sign in / Sign up

Export Citation Format

Share Document