Numerical Investigation of the Thermal Properties of Irregular Foam Structures

2011 ◽  
Vol 312-315 ◽  
pp. 941-946 ◽  
Author(s):  
Seyed Mohammad Hossein Hosseini ◽  
A. Kharaghani ◽  
Christoph Kirsch ◽  
Andreas Öchsner
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Relative Density ◽  
Metal Foams ◽  
Foam Structure ◽  
Open Cell ◽  
Closed Cell ◽  
Effective Thermal Expansion ◽  
Degree Of Irregularity

The thermal properties of irregular open-cell and closed-cell metal foams are investigated via numerical simulation. The influence of relative density and cell irregularity on the thermal conductivity and thermal expansion of the foam structure is determined. It is concluded that the effective thermal conductivity of the foam structure depends linearly on the relative density, whereas no dependence on the degree of irregularity is observed. The effective thermal expansion coefficient of the foam structure is constant for the range of parameters considered.

Numerical Prediction of the Effective Thermal Conductivity of Open- and Closed-Cell Foam Structures

2010 ◽  
Vol 297-301 ◽  
pp. 1210-1217 ◽  
Author(s):  
Seyed Mohammad Hossein Hosseini ◽  
Andreas Öchsner ◽  
Thomas Fiedler
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Relative Density ◽  
Effective Thermal Conductivity ◽  
Linear Trend ◽  
Space Filling ◽  
Open Cell ◽  
Cell Structures ◽  
Closed Cell ◽  
Cell Foam

This paper investigates the thermal properties of metallic open-cell and closed-cell foam structures in space filling and non-space filling configurations. In both, i.e. open-cell and closed-cell structures, a linear trend depending on the relative density has been reported. However the closed-cell structures compared to open-cell ones have a higher thermal conductivity for the same relative density.

Design, Preparation and Thermal Properties of (La0.4Sm0.5Yb0.1)2Zr2O7 Ceramic for Thermal Barrier Coatings

2012 ◽  
Vol 512-515 ◽  
pp. 469-473 ◽  
Author(s):  
L. Liu ◽  
Z. Ma ◽  
F.C. Wang ◽  
Q. Xu
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Rare Earth ◽  
Thermal Expansion Coefficient ◽  
Thermal Barrier Coatings ◽  
Expansion Coefficient ◽  
Phonon Transport ◽  
Thermal Barrier ◽  
Barrier Coatings

According to the theory of phonon transport and thermal expansion, a new complex rare-earth zirconate ceramic (La0.4Sm0.5Yb0.1)2Zr2O7, with low thermal conductivity and high thermal expansion coefficient, has been designed by doping proper ions at A sites. The complex rare-earth zirconate (La0.4Sm0.5Yb0.1)2Zr2O7 powder for thermal barrier coatings (TBCs) was synthesized by coprecipitation-calcination method. The phase, microstructure and thermal properties of the new material were investigated. The results revealed that single phase (La0.4Sm0.5Yb0.1)2Zr2O7 with pyrochlore structure was synthesized. The thermal conductivity and the thermal expansion coefficient of the designed complex rare-earth zirconate ceramic is about 1.3W/m•K and 10.5×10-6/K, respectively. These results imply that (La0.4Sm0.5Yb0.1)2Zr2O7 can be explored as the candidate material for the ceramic layer in TBCs system.

scholarly journals Thermal Properties of Yttrium Aluminum Garnett From Molecular Dynamics Simulations

2011 ◽  
Author(s):  
Majid S. al-Dosari ◽  
D. G. Walker
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Specific Heat ◽  
Molecular Dynamics Simulations ◽  
Yttrium Aluminum Garnet ◽  
System Size ◽  
Yttrium Aluminum ◽  
Dynamics Simulations

Yttrium Aluminum Garnet (YAG, Y3Al5O12) and its varieties have applications in thermographic phosphors, lasing mediums, and thermal barriers. In this work, thermal properties of crystalline YAG where aluminum atoms are substituted with gallium atoms (Y3(Al1−xGax)5O12) are explored with molecular dynamics simulations. For YAG at 300K, the simulations gave values close to experimental values for constant-pressure specific heat, thermal expansion, and bulk thermal conductivity. For various values of x, the simulations predicted no change in thermal expansion, an increase in specific heat, and a decrease in thermal conductivity for x = 50%. Furthermore, the simulations predicted a decrease in thermal conductivity with decreasing system size.

scholarly journals Thermal properties of closed-cell aluminum foam with circular pores

2014 ◽  
Vol 18 (5) ◽  
pp. 1619-1624 ◽  
Author(s):  
Guo-Yun Lu ◽  
Bu-Yun Su ◽  
Zhi-Qiang Li ◽  
Zhi-Hua Wang ◽  
Wei-Dong Song ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Thermal Property ◽  
Cell Size ◽  
Aluminum Foam ◽  
Slight Effect ◽  
Apparent Thermal Conductivity ◽  
Closed Cell ◽  
Simulation Results

The thermal property of closed-cell aluminum foam is studied numerically and the effects of the distribution of the circular pore on the thermal property are studied theoretically. When the convection and radiation are ignored, the effects of porosity, cell size, and distribution forms of pore on the apparent thermal conductivity are investigated. Moreover, the effects of air in the pore on the thermal property are analyzed as well. Simulation results show that apparent thermal conductivity linearly increases with the increase of porosity, while the cell size and the distribution have negligible effects on the thermal property. By comparison, thermal conductivity of air has slight effect on thermal property of foamed aluminum in the context of small size pore.

Primary pyroelectric transition temperatures of binary nitrides (AlN, GaN and InN)

2019 ◽  
Vol 33 (05) ◽  
pp. 1950049
Author(s):  
Muralidhar Swain ◽  
Sushant K. Sahoo ◽  
Bijay K. Sahoo
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Transition Temperature ◽  
Negative Thermal Expansion ◽  
Polarization Field ◽  
Piezoelectric Polarization ◽  
Polarization Mechanism ◽  
Prior Literature

The primary pyroelectric transition temperature of wurtzite nitrides (AlN, GaN and InN) has been explored theoretically from their thermal properties. The spontaneous and piezoelectric polarization modifies the thermal conductivity of nitrides. The thermal conductivity [Formula: see text] as a function of temperature including and excluding the polarization mechanism predicts a transition temperature [Formula: see text] between primary and secondary pyroelectric effects. Below [Formula: see text], thermal conductivity including polarization field [Formula: see text] is lesser than thermal conductivity excluding polarization field [Formula: see text]. This is due to negative thermal expansion in binary nitrides below [Formula: see text]; however, above [Formula: see text], [Formula: see text]. [Formula: see text] is significantly contributed by piezoelectric polarization above [Formula: see text] due to thermal expansion which is the reason for the secondary pyroelectric effect. The transition temperature [Formula: see text] for AlN, GaN and InN has been predicted as 100 K, 70 K and 60 K, respectively, which fit well with the prior literature studies. This report proposes that thermal properties’ study can reveal the role of acoustic phonons in pyroelectricity.

scholarly journals Gas Diffusion Layers in Fuel Cells and Electrolysers: A Novel Semi-Empirical Model to Predict Electrical Conductivity of Sintered Metal Fibres

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 855 ◽  
Author(s):  
Reza Omrani ◽  
Bahman Shabani
Keyword(s):  
Electrical Conductivity ◽  
Fuel Cells ◽  
Gas Diffusion ◽  
Metal Foams ◽  
Critical Porosity ◽  
Gas Diffusion Layers ◽  
Open Cell ◽  
Diffusion Layers ◽  
Sintered Metal ◽  
Closed Cell

This paper introduces novel empirical as well as modified models to predict the electrical conductivity of sintered metal fibres and closed-cell foams. These models provide a significant improvement over the existing models and reduce the maximum relative error from as high as just over 30% down to about 10%. Also, it is shown that these models provide a noticeable improvement for closed-cell metal foams. However, the estimation of electrical conductivity of open-cell metal foams was improved marginally over previous models. Sintered porous metals are widely used in electrochemical devices such as water electrolysers, unitised regenerative fuel cells (URFCs) as gas diffusion layers (GDLs), and batteries. Having a more accurate prediction of electrical conductivity based on variation by porosity helps in better modelling of such devices and hence achieving improved designs. The models presented in this paper are fitted to the experimental results in order to highlight the difference between the conductivity of sintered metal fibres and metal foams. It is shown that the critical porosity (maximum achievable porosity) can play an important role in sintered metal fibres to predict the electrical conductivity whereas its effect is not significant in open-cell metal foams. Based on the models, the electrical conductivity reaches zero value at 95% porosity rather than 100% for sintered metal fibres.

Thermal properties of kinetic spray Al–SiC metal-matrix composite

2003 ◽  
Vol 18 (4) ◽  
pp. 855-860 ◽  
Author(s):  
Gary L. Eesley ◽  
Alaa Elmoursi ◽  
Nilesh Patel
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Metal Matrix ◽  
Volume Fraction ◽  
Spray Deposition ◽  
Deposition Process ◽  
Matrix Composites ◽  
Kinetic Spray ◽  
Compositional Variations

Kinetic spray deposition provides a new means for producing composite materials with tailored physical properties. We report on measurements of the thermal conductivity and thermal-expansion coefficient for several compositional variations of kinetically sprayed Al–SiC metal-matrix composites. As a result of the deposition process, inclusion of SiC particles saturates in the 30–40% volume fraction range.

The Effect of Cell Size on the Physical Properties of Crosslinked Closed Cell Polyethylene Foams Produced by a High Pressure Nitrogen Solution Process

2002 ◽  
Vol 21 (3) ◽  
pp. 165-194 ◽  
Author(s):  
M.A. Rodríguez-Pérez ◽  
J.I. González-Peña ◽  
N. Witten ◽  
J.A. de Saja
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
High Pressure ◽  
Thermal Expansion ◽  
Cell Size ◽  
Mechanical Response ◽  
Solution Process ◽  
Strain Rates ◽  
Dynamic Mechanical ◽  
Closed Cell

The thermal conductivity, thermal expansion, mechanical properties at low strain rates and dynamic mechanical properties of a collection of crosslinked closed cell polyethylene foams manufactured by a high pressure nitrogen solution process have been studied as a function of the cell size. The main mechanisms that influence each property and the foam microstructure have been considered to rationalise the results. A theoretical model has been used to examine the thermal conductivity values. The results have shown the extent to which reducing the cell size could improve the insulating capabilities of these materials. The effect of cell size on the mechanical properties at low strain rates is very small, as a consequence the thermal expansion does not depend on cell size. Nevertheless, the structural characteristics are seen to influence dynamic mechanical response at temperatures below 15°C.

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