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.

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.

Porosity and Effective Thermal Conductivity of Wire Screens

1990 ◽  
Vol 112 (1) ◽  
pp. 5-9 ◽  
Author(s):  
Won Soon Chang
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Theoretical Model ◽  
Effective Thermal Conductivity ◽  
Present Model ◽  
Model Based ◽  
Wire Screen ◽  
Simple Theoretical Model ◽  
Parallel Conduction ◽  
The Wire

A simple theoretical model based on combined series and parallel conduction for the effective thermal conductivity of fluid-saturated screens has been developed. The present model has been compared with the existing correlations and experimental data available in literature, and it has been found that the model is effective in predicting thermal conductivity. The study also demonstrates that it is important to include the actual thickness of the wire screen in order to calculate the porosity accurately.

scholarly journals Effective thermal conductivity modeling with primary and secondary parameters for two-phase materials

2010 ◽  
Vol 14 (2) ◽  
pp. 393-407 ◽  
Author(s):  
Kumar Palaniswamy ◽  
Raja Venugopal ◽  
Karthikeyan Palaniswamy
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Unit Cell ◽  
Maximum Deviation ◽  
Algebraic Equations ◽  
Two Phase ◽  
Wide Range ◽  
Maximum Conductivity ◽  
Spatially Periodic

In this article, the collocated parameter models are used to estimate the effective thermal conductivity of the two-phase materials including the effect of various inclusions in the unit cell. The algebraic equations are derived using unit cell based isotherm approach for two dimensional spatially periodic medium. The geometry of the medium is considered as a matrix of touching and non-touching in-line octagon and hexagon cylinders. The models are used to predict the thermal conductivity of numerous two-phase materials (maximum conductivity ratio of 1000 and concentration ranging between 0 and 1). The estimated thermal conductivity data is in good agreement with the experimental data within ?15.84%, ?18.14% maximum deviation, respectively, from octagon and hexagon cylinders for various two-phase systems. The obtained results are compared with a wide range of experimental data for various geometrical configurations to estimate the effective thermal conductivity of two-phase materials.

scholarly journals Effect of Compression on the Effective Thermal Conductivity and Thermal Contact Resistance in PEM Fuel Cell Gas Diffusion Layers

2010 ◽  
Author(s):  
Ehsan Sadeghi ◽  
Ned Djilali ◽  
Majid Bahrami
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Fuel Cell ◽  
Contact Resistance ◽  
Effective Thermal Conductivity ◽  
Thermal Contact Resistance ◽  
Thermal Contact ◽  
Pem Fuel Cell ◽  
Gas Diffusion ◽  
Analytical Models

Heat transfer through the gas diffusion layer (GDL) of a PEM fuel cell is a key process in the design and operation a PEM fuel cell. The analysis of this process requires determination of the effective thermal conductivity as well as the thermal contact resistance between the GDL and adjacent surfaces/layers. In the present study, a guarded-hot-plate apparatus has been designed and built to measure the effective thermal conductivity and thermal contact resistance in GDLs under vacuum and atmospheric pressure. Toray carbon papers with the porosity of 78% and different thicknesses are used in the experiments under a wide range of compressive loads. Moreover, novel analytical models are developed for the effective thermal conductivity and thermal contact resistance and compared against the present experimental data. Results show good agreements between the experimental data and the analytical models. It is observed that the thermal contact resistance is the dominant component of the total thermal resistance and neglecting this phenomenon may result in enormous errors.

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.

A Model of Effective Thermal Conductivity for Planting Soil of Green Roof

2012 ◽  
Vol 174-177 ◽  
pp. 2065-2070
Author(s):  
Shu Kui Zheng ◽  
Ming Fang Tang ◽  
Zhen Jing Yang
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Mathematical Model ◽  
Effective Thermal Conductivity ◽  
Green Roof ◽  
High Accuracy ◽  
Climatic Conditions ◽  
Model Accuracy ◽  
Wide Range ◽  
Simplified Mathematical Model

For insulation, green roof has been widely applied and researched in recent years. The effective thermal conductivity (ETC) of planting soil of green roof plays an important role to insulation. The ETC of six kinds of compound planting soil, usually used in green roof，were measured with different water content. The results show that the ETC of compound planting soils has linear relationship with weight humidity. A sensible, albeit simplified mathematical model, with weight humidity and dry apparent density as variables, was established for the dynamic ETC of compound planting soil. To verify model accuracy, the calculation data of ETC of compound planting soil, which under natural climatic conditions for 2 years, were compared with experimental data, and the results indicate that the model have high accuracy in a wide range of weight humidity. In additional, the ETC proper range of compound planting soil was derived.

Effective Thermal Conductivity Within Packed Beds of Spherical Particles

1989 ◽  
Vol 111 (4) ◽  
pp. 830-836 ◽  
Author(s):  
A. B. Duncan ◽  
G. P. Peterson ◽  
L. S. Fletcher
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Elastic Limit ◽  
Soft Materials ◽  
Analytical Models ◽  
Spherical Particles ◽  
Experimental Program ◽  
Packed Beds ◽  
Bed Material ◽  
Thermal Conductivities

An investigation of the effective thermal conductivity of packed beds of spherical particles was conducted. Included is a brief review of related analytical and experimental investigations, along with a description of the results from an experimental program. Five beds of different materials were evaluated to determine the effective thermal conductivity as a function of the mechanical load on the bed, the conductivity of the bed material, and the interstitial gaseous environment surrounding the bed particles. The effective thermal conductivity of the packed beds were found to be dependent upon the thermal conductivity of the bed material and the axial load. The presence of an interstitial gas increased the effective thermal conductivity of the bed by a factor of two in almost all cases. The experimental results obtained for vacuum conditions were compared with two existing analytical models that assumed elastic deformation of the spheres. The analytical models slightly under-predicted the effective thermal conductivity for hard materials with low thermal conductivities below the elastic limit, and slightly overpredicted the effective thermal conductivity above the elastic limit for these materials. For soft materials with relatively high thermal conductivities, the analytical models overpredicted the effective thermal conductivity by as much as an order of magnitude.

Temperature and Pressure Dependences of the Effective Thermal Conductivity of Granites

2020 ◽  
Vol 84 (9) ◽  
pp. 1144-1146
Author(s):  
S. N. Emirov ◽  
A. A. Aliverdiev ◽  
V. D. Beybalaev ◽  
A. A. Amirova ◽  
R. M. Aliev ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Temperature And Pressure
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