Self-Consistent Open-Celled Metal Foam Model for Thermal Applications

2006 ◽  
Vol 128 (11) ◽  
pp. 1194-1203 ◽  
Author(s):  
Eric N. Schmierer ◽  
Arsalan Razani
Keyword(s):  
Thermal Conductivity ◽  
Granular Material ◽  
Metal Foam ◽  
Foam Cell ◽  
Geometric Model ◽  
Active Material ◽  
Diameter Distribution ◽  
Thermal Conductivity Ratio ◽  
High Porosity ◽  
Self Consistent

Many engineering applications require thermal cycling of granular materials. Since these materials generally have poor effective thermal conductivity various techniques have been proposed to improve bed thermal transport. These include insertion of metal foam with the granular material residing in the interstitial space. The use of metal foam introduces a parasitic thermal capacitance, disrupts packing, and reduces the amount of active material. In order to optimize the combined high porosity metal foam-granular material matrix and study local thermal nonequilibrium, multiple energy equations are required. The interfacial conductance coefficients, specific interface area, and the effective thermal conductivities of the individual components, which are required for a multiple energy equation analysis, are functions of the foam geometry. An ideal three-dimensional geometric model of open-celled Duocell® foam is proposed. Computed tomography is used to acquire foam cell and ligament diameter distribution, ligament shape, and specific surface area for a range of foam parameters to address various shortcomings in the literature. These data are used to evaluate the geometric self-consistency of the proposed geometric model with respect to the intensive and extensive geometry parameters. Experimental thermal conductivity data for the same foam samples are acquired and are used to validate finite element analysis results of the proposed geometric model. A simple relation between density and thermal conductivity ratio is derived using the results. The foam samples tested exhibit a higher dependence on relative density and less dependence on interstitial fluid than data in the literature. The proposed metal foam geometric model is shown to be self-consistent with respect to both its geometric and thermal properties.

Numerical Study of Heat Conduction of High Porosity Open-Cell Metal Foam/Paraffin Composite at Pore Scale

2016 ◽  
Author(s):  
Yuanpeng Yao ◽  
Huiying Wu ◽  
Zhenyu Liu
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Pore Size ◽  
Metal Foam ◽  
Foam Cell ◽  
High Porosity ◽  
Pore Scale ◽  
Thermal Equilibrium State ◽  
Foam Structure ◽  
Open Cell

In this paper, a numerical model employing 3D foam structure represented by Weaire-Phelan foam cell is developed to study the steady heat conduction of high porosity open-cell metal foam/paraffin composite at the pore-scale level. Two conduction problems are considered in the cubic representative computation unit of the composite material: one with constant temperature difference between opposite sides of the cubic unit (that can be used to determine the effective thermal conductivity (ETC)) and the second with constant heat flux at the interface between metal foam and paraffin (that can be used to determine the interstitial conduction heat transfer coefficient (ICHTC)). The effects of foam pore structure parameters (pore size and porosity) on heat conduction are investigated for the above two problems. Results show that for the first conduction problem, the effect of foam structure on heat conduction (i.e. the ETC) is related to porosity rather than pore size. The essential reason is due to the thermal equilibrium state between metal foam and paraffin indicated by the negligible interstitial heat transfer. While for the second conduction problem with inherent thermal non-equilibrium effect, it shows that both porosity and pore size significantly influence the interstitial heat conduction (i.e. the ICHTC). Furthermore, the present ETC and ICHTC data are compared to the results in the published literature. It shows that our ETC data agree well with the reported experimental results, and are more accurate than the numerical predications based on body-centered-cubic foam cell in literature. And our ICHTC data are in qualitative agreement with the published numerical results, but the present results are based on a more realistic foam structure.

scholarly journals Characterisation of Flow and Heat Transfer in Sintered Metal Foams

2008 ◽  
Author(s):  
Jo¨rg Sauerhering ◽  
Stefanie Angel ◽  
Thomas Fend ◽  
Stefan Brendelberger ◽  
Elena Smirnova ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Combustion Chamber ◽  
Gas Turbines ◽  
Metal Foam ◽  
High Porosity ◽  
Transfer Coefficients ◽  
Sintered Metal ◽  
Flow And Heat Transfer ◽  
Wall Element

Since sintered metal foam is an innovative material with promising properties such as high porosity, good thermal conductivity, beneficial mechanical properties like strength and weldability, it has been considered to be applied as an open porous wall element in combustion chambers of gas turbines. In this application, the foam serves as a functional material capable to lead cooling air through micro- and minichannels into the inside of the combustion chamber. This cooling technique also known as effusion cooling keeps the combustion chamber walls below critical temperatures and therefore enables the burning process to be more effectively operated at higher temperatures. For a proper design of the wall element, the temperature distribution along the path of the fluid inside the foam must be known. For an exact calculation of the temperature flow and heat transfer processes inside the foam must be known. Therefore in this study the permeability and heat transfer properties of the foam have been characterized experimentally. The methods are described and the results in terms of permeability coefficients, convective heat transfer coefficients and effective thermal conductivity are presented as functions of the foam’s porosity. The method of the calculation is described and finally, the results of the calculation are presented, showing that due to the fine grained structure of the foam, the heat transfer from the solid to the cooling fluid takes place in a thin layer close to the inner surface of the camber wall.

Characterization of High Porosity Open-Celled Metal Foam Using Computed Tomography

2004 ◽  
Author(s):  
Eric N. Schmierer ◽  
Arsalan Razani ◽  
Scott Keating ◽  
Tony Melton
Keyword(s):  
Heat Transfer ◽  
Computed Tomography ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Surface Area ◽  
Metal Foam ◽  
Three Dimensional ◽  
Metal Foams ◽  
High Porosity ◽  
Interfacial Surface

High porosity metal foams have been the subject of many investigations for use in heat transfer enhancement through increased effective thermal conductivity and surface area. Convection heat transfer applications with these foams have been investigated for a large range of Reynolds numbers. Common to these analyses is the need for quantitative information about the interfacial surface area and the effective thermal conductivity of the metal foam. The effective thermal conductivity of these metal foams have been well characterized, however little investigation has been made into the actual surface area of the foam and its dependence on the foam pore density and porosity. Three-dimensional x-ray computed tomography (CT) is used for determining interfacial surface area and ligament diameter of metal foam with porosities ranging from 0.85 to 0.97 and pore densities of 5, 10, 20, and 40 pores per inch. Calibration samples with known surface area and volume are utilized to benchmark the CT process. Foam results are compared to analytical results obtained from the development of a three-dimensional model of the high porosity open-celled foam. The results obtained are compared to results from previous investigations into these geometric parameters. Results from calibration sample comparison and analysis of the foam indicate the need for additional work in quantifying the repeatability and sources of error in CT measurement process.

Study of Micro-Structure Based Effective Thermal Conductivity of Graphite Foam

2016 ◽  
Author(s):  
Yue Chai ◽  
Xiaohu Yang ◽  
Xiangzhao Meng ◽  
Qunli Zhang ◽  
Liwen Jin
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Effective Thermal Conductivity ◽  
Analytical Model ◽  
Geometric Model ◽  
Three Dimensional ◽  
Heat Sinks ◽  
High Porosity ◽  
Geometry Model ◽  
Graphite Foam

As a new type of functional material, porous graphite foam exhibits unique thermal physical properties and geometric characteristics in heat transfer applications. It has the advantages of low density, high specific surface area, high porosity and high bulk thermal conductivity, which can be used as the core component of small, lightweight, compact and efficient heat sinks. Effective thermal conductivity serves one of the key thermophysical properties for foam-cored heat sinks. The complex three-dimensional topology and interstitial fluids significantly affect the heat conduction through such kind of porous structures, reflecting a topologically based effective thermal conductivity. This paper presents a novel geometric model for representing the microstructure of graphite foams, with simplifications and modifications made on the actual pore structure of graphite foam. For calculation simplicity, we convert the realized geometry consisting of complex surfaces and tortuous ligaments into a simplified geometry with circular ligaments joined at cuboid nodes, on the basis of the volume equivalency rule. The multiple-layer method is used to divide the proposed geometry into solvable areas and the series-parallel relations are used to derive the analytical model for effective thermal conductivity. To physically explore the heat conduction mechanisms at pore scale, direction numerical simulations were conducted on the reconstructed geometric model. Achieving good agreement with experimental data, the present analytical model (based on the simplified geometry) is validated. Further, the numerically simulated conductivities follow the model prediction, favoring thermally that the two geometries are equal. The present geometry model is more realized and capable of reflecting the internal microstructure of graphite foam, which will benefit the understandings for the thermo-physical mechanisms of pore-scaled heat conduction and micro structures of graphite foam.

Fabrication of High Porosity Mullite Foams and their Thermal Properties

2016 ◽  
Vol 879 ◽  
pp. 1987-1991
Author(s):  
Toru Shimizu ◽  
Kunio Matsuzakaki
Keyword(s):  
Thermal Conductivity ◽  
Room Temperature ◽  
Metal Foam ◽  
High Porosity ◽  
Refractory Brick ◽  
Thermal Insulating ◽  
Slurry Method ◽  
Mullite Refractory ◽  
Refractory Bricks ◽  
Insulating Properties

Already, we developed a high porosity alumina foam. However, alumina has high thermal conductivity about 36W/mK at room temperature, and it need to achieve to high porosity to decrease thermal conductivity to for application of refractory bricks. Therefore, high porosity mullite refractory brick is developed using GS (Gelation of Slurry) method that is already developed for production of high porosity metal foam. Appling this method to production of mullite foams, the ceramics foams from 93 to 97% porosity can be produced. Also, their thermal conductivities are proportional to densities and obey to Ashby-Glicksman model. Its thermal conductivity is about 0.07W/mK when density is 0.1 g/cm3. The high porosity mullite foams achieved enough thermal insulating properties for refractory brick.

scholarly journals Natural Convection in Annulus Between Two Concentric Cylinders Partially Filled with Metal Foam Distributed with New Suggested Design

2022 ◽  
Vol 961 (1) ◽  
pp. 012032
Author(s):  
Israa H Alkinani ◽  
Luma Fadhil Ali
Keyword(s):  
Thermal Conductivity ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Metal Foam ◽  
Current Model ◽  
Local Thermal Equilibrium ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Annular Space ◽  
Concentric Cylinders

Abstract The investigation of natural convection in an annular space between two concentric cylinders partially filled with metal foam is introduced numerically. The metal foam is inserted with a new suggested design that includes the distribution of metal foam in the annular space, not only in the redial direction, but also with the angular direction. Temperatures of inner and outer cylinders are maintained at constant value in which inner cylinder temperature is higher than the outer one. Naiver Stokes equation with Boussinesq approximation is used for fluid regime while Brinkman-Forchheimer Darcy model used for metal foam. In addition, the local thermal equilibrium condition in the energy equation of the porous media is presumed to be applicable for the present investigation. CFD ANSYS FLUENT software package (version 18.2) is used as a solver to this problem. Various parameters are examined; Rayleigh number, Darcy number, and thermal conductivity ratio to study the effect of them on fluid flow and heat transfer inside the annuli space in the suggested design of metal foam layer. current model is compared with the available published results and good agreement is noticed. Results showed that as Rayleigh number increases the dominated of convection mode increases and Nusselt increases. Also, Nusselt is larger at the higher Darcy and thermal conductivity ratio. It was found that at Rayleigh of 106 and thermal conductivity ratio of 104 Nusselt reach its higher value which is 6.69 for Darcy of 0.1 and 6.77 for Darcy of 0.001. A comparison between this design and the traditional design was established for Darcy 0.001 and thermal conductivity ratio 102, and its showed a good enhancement in Nusselt number and the greatest enhancement percentage was 44% at Rayleigh equal 5*104 while the lowest percentage is 6% for Rayleigh equal106.

Effects of anisotropy and solid/liquid thermal conductivity ratio during inverted Bridgman growth

2002 ◽  
Author(s):  
Julaporn Kaenton ◽  
Victoria Timchenko ◽  
Mohammed El Ganaoui ◽  
Graham de Vahl Davis ◽  
Eddie Leonardi ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Bridgman Growth ◽  
Liquid Thermal Conductivity ◽  
Solid Liquid

scholarly journals Effects of the Wall Properties on the Cooling Efficiency in a Thermosyphon Containing PCM Suspensions

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 572
Author(s):  
Ching-Jenq Ho ◽  
Shih-Ming Lin ◽  
Chi-Ming Lai
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Wall Thickness ◽  
Thermal Conductivity Ratio ◽  
Heat Transfer Efficiency ◽  
Wall Properties ◽  
Heating Section ◽  
Cooling Section ◽  
Optimum Heat ◽  
Parameter Ranges

This study explores the effects of pipe wall properties (thermal conductivity k and wall thickness tw) on the heat transfer performance of a rectangular thermosyphon with a phase change material (PCM) suspension and a geometric configuration (aspect ratio = 1; dimensionless heating section length = 0.8; dimensionless relative elevation between the cooling and the heating sections = 2) that ensures the optimum heat transfer efficiency in the cooling section. The following parameter ranges are studied: the dimensionless loop wall thickness (0 to 0.5), wall-to-fluid thermal conductivity ratio (0.1 to 100), modified Rayleigh number (1010 to 1011), and volumetric fraction of PCM particles (0 to 10%). The results show that appropriate selection of k and tw can lead to improved heat transfer effectiveness in the cooling section of the PCM suspension-containing rectangular thermosyphon.

scholarly journals The Equivalent Thermal Conductivity of the Micro/Nano Scaled Periodic Cubic Frame Silver and Its Thermal Radiation Mechanism Analysis

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4158
Author(s):  
Haiyan Yu ◽  
Haochun Zhang ◽  
Heming Wang ◽  
Dong Zhang
Keyword(s):  
Thermal Conductivity ◽  
Thermal Radiation ◽  
Cell Size ◽  
Near Infrared ◽  
High Porosity ◽  
Mechanism Analysis ◽  
Infrared Band ◽  
Spectral Radiation ◽  
Radiation Mechanism ◽  
Equivalent Thermal Conductivity

Currently, there are few studies on the influence of microscale thermal radiation on the equivalent thermal conductivity of microscale porous metal. Therefore, this paper calculated the equivalent thermal conductivity of high-porosity periodic cubic silver frame structures with cell size from 100 nm to 100 µm by using the microscale radiation method. Then, the media radiation characteristics, absorptivity, reflectivity and transmissivity were discussed to explain the phenomenon of the radiative thermal conductivity changes. Furthermore, combined with spectral radiation properties at the different cross-sections and wavelength, the radiative transmission mechanism inside high-porosity periodic cubic frame silver structures was obtained. The results showed that the smaller the cell size, the greater radiative contribution in total equivalent thermal conductivity. Periodic cubic silver frames fluctuate more in the visible band and have better thermal radiation modulation properties in the near infrared band, which is formed by the Surface Plasmon Polariton and Magnetic Polaritons resonance jointly. This work provides design guidance for the application of this kind of periodic microporous metal in the field of thermal utilization and management.

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