Influence of Contact Mechanics in the Prediction of the Effective Thermal Conductivity of Spheroid Packed Beds

2003 ◽  
Author(s):  
G. Buonanno ◽  
A. Carotenuto ◽  
G. Giovinco ◽  
L. Vanoli
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Statistical Approach ◽  
Thermal Contact ◽  
Peak Height ◽  
Thermal Contact Conductance ◽  
Curvature Radius ◽  
Packed Beds ◽  
Wide Range ◽  
Thermal Phenomena

Thermal contact conductance is an important parameter in a wide range of thermal phenomena, and consequently a large number of experimental, numerical and statistical investigations have been carried out in literature. In the present paper an analysis of thermal contact resistance is carried out to predict heat transfer between spherical rough surfaces in contact, by means of a statistical approach. The micro-geometry of the surface is described through a probabilistic model based on the peak height variability and invariant asperity curvature radius. The numerical model has been applied to evaluate the effective thermal conductivity of packed beds of steel spheroids and validated through the comparison with the experimental data obtained by means of an apparatus designed and build up for this purpose.

Compact Analytical Models of Effective Thermal Conductivity of Rough Spheroid Packed Beds

2004 ◽  
Author(s):  
M. Bahrami ◽  
M. M. Yovanovich ◽  
J. R. Culham
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Present Model ◽  
Thermal Analyses ◽  
Contact Load ◽  
Analytical Models ◽  
Packed Beds ◽  
Wide Range ◽  
Temperature And Pressure

New compact analytical models for predicting the effective thermal conductivity of regularly packed beds of rough spheres immersed in a stagnant gas are developed. Existing models do not consider either the influence of the spheres roughness or the rarefaction of the interstitial gas on the conductivity of the beds. Contact mechanics and thermal analyses are performed for uniform size spheres packed in SC and FCC arrangements and the results are presented in the form of compact relationships. The present model accounts for the thermophysical properties of spheres and the gas, contact load, spheres diameter, spheres roughness and asperities slope, and temperature and pressure of the gas. The present model is compared with experimental data for SC and FCC packed beds and good agreement is observed. The experimental data cover a wide range of the contact load, surface roughness, interstitial gas type, and gas temperature and pressure.

Measurement of the Thermal Contact Conductance and Thermal Conductivity of Anodized Aluminum Coatings

1990 ◽  
Vol 112 (3) ◽  
pp. 579-585 ◽  
Author(s):  
G. P. Peterson ◽  
L. S. Fletcher
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Coating Thickness ◽  
Thermal Contact ◽  
Thermal Contact Conductance ◽  
Aluminum Surface ◽  
Anodized Aluminum ◽  
Contact Conductance ◽  
Surface Measurements

An experimental investigation was conducted to determine the thermal contact conductance and effective thermal conductivity of anodized coatings. One chemically polished Aluminum 6061-T6 test specimen and seven specimens with anodized coatings varying in thickness from 60.9 μm to 163.8 μm were tested while in contact with a single unanodized aluminum surface. Measurements of the overall joint conductance, composed of the thermal contact conductance between the anodized coating and the bare aluminum surface and the bulk conductance of the coating material, indicated that the overall joint conductance decreased with increasing thickness of the anodized coating and increased with increasing interfacial load. Using the experimental data, a dimensionless expression was developed that related the overall joint conductance to the coating thickness, the surface roughness, the interfacial pressure, and the properties of the aluminum substrate. By subtracting the thermal contact conductance from the measured overall joint conductance, estimations of the effective thermal conductivity of the anodized coating as a function of pressure were obtained for each of the seven anodized specimens. At an extrapolated pressure of zero, the effective thermal conductivity was found to be approximately 0.02 W/m-K. In addition to this extrapolated value, a single expression for predicting the effective thermal conductivity as a function of both the interface pressure and the anodized coating thickness was developed and shown to be within ±5 percent of the experimental data over a pressure range of 0 to 14 MPa.

scholarly journals In-Plane Thermal Conductivity of PEM Fuel Cell Gas Diffusion Layers

2011 ◽  
Author(s):  
Ehsan Sadeghi ◽  
Ned Djilali ◽  
Majid Bahrami
Keyword(s):  
Thermal Conductivity ◽  
Fuel Cell ◽  
Effective Thermal Conductivity ◽  
Thermal Contact ◽  
Pem Fuel Cell ◽  
Gas Diffusion ◽  
Carbon Paper ◽  
Test Bed ◽  
Diffusion Layers ◽  
Wide Range

Heat transfer through the gas diffusion layer (GDL) is a key process in the design and operation of a PEM fuel cell. The analysis of this process requires determination of the effective thermal conductivity. This transport property differs significantly in the through-plane and in-plane directions due to the anisotropic micro-structure of the GDL. In the present study, a novel test bed that allows the separation of in-plane effective thermal conductivity and thermal contact resistance in GDLs is described. Measurements are performed using Toray carbon paper TGP-H-120 samples for a range of PTFE content at a mean temperature of 65–70°C. The measurements are complemented by a compact analytical model that achieves good agreement with the experimental data. The in-plane effective thermal conductivity is found to be about 12 times higher than the through-plane conductivity and remains approximately constant, k ≈ 17.5 W/mK, over a wide range of PTFE content.

A Boundary Element Method for Evaluation of the Effective Thermal Conductivity of Packed Beds

2006 ◽  
Vol 129 (3) ◽  
pp. 363-371 ◽  
Author(s):  
Jianhua Zhou ◽  
Aibing Yu ◽  
Yuwen Zhang
Keyword(s):  
Thermal Conductivity ◽  
Boundary Element ◽  
Effective Thermal Conductivity ◽  
Fluid Phase ◽  
Packed Bed ◽  
Element Model ◽  
Solid Surfaces ◽  
Packed Beds ◽  
Wide Range ◽  
Radiation Heat Exchange

The problem of evaluating the effective thermal conductivity of random packed beds is of great interest to a wide-range of engineers and scientists. This study presents a boundary element model (BEM) for the prediction of the effective thermal conductivity of a two-dimensional packed bed. The model accounts for four heat transfer mechanisms: (1) conduction through the solid; (2) conduction through the contact area between particles; (3) radiation between solid surfaces; and (4) conduction through the fluid phase. The radiation heat exchange between solid surfaces is simulated by the net-radiation method. Two regular packing configurations, square array and hexagonal array, are chosen as illustrative examples. The comparison between the results obtained by the present model and the existing predictions are made and the agreement is very good. The proposed BEM model provides a new tool for evaluating the effective thermal conductivity of the packed beds.

Enhancement of Thermal Contact Conductance by Metallic Coatings: Theory and Experiment

1985 ◽  
Vol 107 (3) ◽  
pp. 513-519 ◽  
Author(s):  
V. W. Antonetti ◽  
M. M. Yovanovich
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Glass Bead ◽  
Thermal Contact ◽  
The Other ◽  
Thermal Contact Conductance ◽  
Thermomechanical Model ◽  
Thermal Test ◽  
Test Points ◽  
Theory And Experiment

A thermomechanical model for nominally flat, rough contacting surfaces coated with a metallic layer is developed. The model is shown to agree quite well with thermal test data obtained using nickel specimens, with one side of the contact coated with silver and the other side glass-bead blasted. In addition, it is demonstrated that a coated joint can be reduced to an equivalent bare joint by employing an effective hardness and an effective thermal conductivity. Using this technique, 61 coated test points were correlated, with an RMS difference of ± 12.6 percent between the data and a correlation which had previously been used only for bare contacts.

Thermal Contact Conductance of a Bone-Dry Paper Handsheet/Metal Interface

1992 ◽  
Vol 114 (2) ◽  
pp. 326-330 ◽  
Author(s):  
J. Seyed-Yagoobi ◽  
K. H. Ng ◽  
L. S. Fletcher
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Water Retention ◽  
Thermal Contact ◽  
Thermal Contact Conductance ◽  
Metal Interface ◽  
Contact Conductance ◽  
Interface Contact ◽  
Sheet Density

An apparatus was constructed for determination of the thermal contact conductance for a paper handsheet/metal interface and for measurement of the effective thermal conductivity of handsheet samples. Bone-dry Bleached Southern Mixed Kraft hand-sheets with a water retention value of 1.832 were used to study the effect of pressure on thermal contact conductance and to measure the effective thermal conductivity of samples at various sheet density levels. A regression model describing the interface thermal contact conductance as a function of pressure and basis weight was derived. The contact conductance increases with increasing pressure or with decreasing basis weight. At a pressure of 2.3 kPa, the value of the interface contact conductance for the bone-dry samples considered ranges from approximately 97 W/m2K for a sheet of 348.7 g/m2 basis weight to 200 W/m2K for a sheet of 68.0 g/m2 basis weight. For pressures near 300 kPa, these values increase to 146 and 452 W/m2K, respectively. The effective thermal conductivity of the handsheet samples was derived from measured values of overall joint conductance and interface contact conductance. The results indicate that the thermal conductivity of the bone-dry samples increases with increasing sheet density, ranging from 0.14 W/mK to 0.70 W/mK for sheet densities of 90 kg/m3 to 500 kg/m3, respectively, for the samples considered.

scholarly journals Microstructure Dependence of Effective Thermal Conductivity of EB-PVD TBCs

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 1838
Author(s):  
Shi-Yi Qiu ◽  
Chen-Wu Wu ◽  
Chen-Guang Huang ◽  
Yue Ma ◽  
Hong-Bo Guo
Keyword(s):  
Thermal Conductivity ◽  
Mechanical Stress ◽  
Effective Thermal Conductivity ◽  
Thermal Insulation ◽  
Inclination Angle ◽  
Physical Vapor Deposition ◽  
Thermal Contact ◽  
Mathematic Model ◽  
Columnar Structure ◽  
Structural Parameter

Microstructure dependence of effective thermal conductivity of the coating was investigated to optimize the thermal insulation of columnar structure electron beam physical vapor deposition (EB-PVD coating), considering constraints by mechanical stress. First, a three-dimensional finite element model of multiple columnar structure was established to involve thermal contact resistance across the interfaces between the adjacent columnar structures. Then, the mathematical formula of each structural parameter was derived to demonstrate the numerical outcome and predict the effective thermal conductivity. After that, the heat conduction characteristics of the columnar structured coating was analyzed to reveal the dependence of the effective thermal conductivity of the thermal barrier coatings (TBCs) on its microstructure characteristics, including the column diameter, the thickness of coating, the ratio of the height of fine column to coarse column and the inclination angle of columns. Finally, the influence of each microstructural parameter on the mechanical stress of the TBCs was studied by a mathematic model, and the optimization of the inclination angle was proposed, considering the thermal insulation and mechanical stress of the coating.

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