scholarly journals Thermal Dispersion in Porous Media—A Review on the Experimental Studies for Packed Beds

2013 ◽  
Vol 65 (3) ◽  
Author(s):  
Türküler Özgümüş ◽  
Moghtada Mobedi ◽  
Ünver Özkol ◽  
Akira Nakayama
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Porous Media ◽  
Effective Thermal Conductivity ◽  
Experimental Studies ◽  
Experimental Methods ◽  
Packed Beds ◽  
Thermal Dispersion ◽  
Heat Addition

Thermal dispersion is an important topic in the convective heat transfer in porous media. In order to determine the heat transfer in a packed bed, the effective thermal conductivity including both stagnant and dispersion thermal conductivities should be known. Several theoretical and experimental studies have been performed on the determination of the effective thermal conductivity. The aim of this study is to review the experimental studies done on the determination of the effective thermal conductivity of the packed beds. In this study, firstly brief information on the definition of the thermal dispersion is presented and then the reported experimental studies on the determination of the effective thermal conductivity are summarized and compared. The reported experimental methods are classified into three groups: (1) heat addition/removal at the lateral boundaries, (2) heat addition at the inlet/outlet boundary, (3) heat addition inside the bed. For each performed study, the experimental details, methods, obtained results, and suggested correlations for the determination of the effective thermal conductivity are presented. The similarities and differences between experimental methods and reported studies are shown by tables. Comparison of the correlations for the effective thermal conductivity is made by using figures and the results of the studies are discussed.

SPH as an Inverse Numerical Tool for the Prediction of Diffusive Properties in Porous Media

2007 ◽  
Vol 553 ◽  
pp. 171-189 ◽  
Author(s):  
Antonio C.M. Sousa ◽  
Fangming Jiang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Porous Media ◽  
Fluid Flow ◽  
Effective Thermal Conductivity ◽  
Pore Scale ◽  
Relative Arrangement ◽  
Inclusion Shape ◽  
Micro Structures ◽  
Bulk Thermal Conductivity

Heat and mass transfer and fluid flow in porous media are usually characterized by, or associated with, the effective thermal conductivity, the effective mass diffusivity and the permeability, respectively. All these macroscopic quantities are conceptually established on a phenomenological “equivalence” basis. They may contain the influence of porous micro-structures upon the corresponding diffusive process; however, the detailed nature inside the porous medium is lumped and neglected. Pore scale numerical modelling has the potential of providing adequate meso-/micro- scale insight into the transport process in porous medium, as well as obtaining macroscopic properties, which can encompass the complex pore-structure details. Modelling heat/mass transfer and fluid flow in complicated porous micro-structures presents a major challenge to numerical methods due to their multiscale and multiphysics nature. A relatively-novel numerical technique - the meshless Lagrangian-based Smoothed Particle Hydrodynamics (SPH) method is thought to be capable of making a significant contribution to this research field. This work deals primarily with the SPH modelling of heat conduction and fluid flow in 2-D isotropic porous media. The porous matrix is formed by randomly including a different component into a base component. Various pore-structures are realized by changing the inclusion shape/size, or the relative arrangement condition between inclusions. Pore-scale heat transfer and fluid flow streams are visualized, and both heat transfer and fluid flow always follow, as expected, the paths of least resistance through the porous structures. In what concerns the effective thermal conductivity, for the porous media with the base component of larger bulk thermal conductivity, the “flexible” EMT model, which can accommodate, to some extent, the influence from the porous micro-structures on the effective thermal conductivity by adjusting the so-called flexible factor ff, gives effective thermal conductivities agreeable to the SPH predictions across the whole composition range if ff is taken to be ~ 4.5; the effective thermal conductivity shows a weak dependence on the inclusion shape/size and the relative arrangement condition between inclusions; however, for porous media with dispersed inclusions, which component has larger bulk thermal conductivity presents a strong effect upon the effective thermal conductivity. The SPH fluid flow simulation results confirm the macroscopic Darcy’s law to be valid only in the creeping flow regime; the dimensionless permeability (normalized by the squared characteristic dimension of the inclusions) is found to have an exponential dependence on the porosity within the intermediate porosity range, and the derived dimensionless permeability /""porosity relation is found to have only a minor dependence on either the relative arrangement condition between inclusions or the inclusion shape/area.

Design and Optimization of Temperature Acquisition System for Determination of Effective Thermal Conductivity of Pebble Bed

2017 ◽  
Author(s):  
Pengxin Cheng ◽  
Cheng Ren ◽  
Yongyong Wu ◽  
Rui Li
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Data Acquisition ◽  
Effective Thermal Conductivity ◽  
Data Acquisition System ◽  
Acquisition System ◽  
Test Facility ◽  
Software Systems ◽  
Pebble Bed

A full-scale heat transfer test facility has been designed and built for the determination of effective thermal conductivity of pebble bed, which is a macroscopic parameter to characterize the heat transfer capacity of the core in the High Temperature Gas-Cooled Reactor. The data acquisition system is developed to collect, display and record the temperature data in monitoring points. Two alternative software systems are designed to obtain better performance. To enhance precision of the measurement system, several aspects are analyzed and optimized in the implementation of LabVIEW. The error of the hardware system is analyzed, which is within the acceptable range. The data acquisition system can meet the practical demands of temperature acquisition in the range of thermal analysis.

Determination of Thermal Conductivity of Mn-Al Powder Compacts using An Inverse Heat Transfer Procedure

2012 ◽  
Vol 31 (4-5) ◽  
pp. 581-592
Author(s):  
Zhi Li ◽  
Stavros A. Argyropoulos
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Powder Compact ◽  
Effect Of Temperature ◽  
Inverse Heat Transfer ◽  
Al Powder ◽  
Powder Compacts ◽  
Thermal Conductivities

AbstractThe effective thermal conductivities of various Mn-Al powder compact compositions were measured using an Inverse Heat Transfer Procedure, and extensive validation work was also carried out. Specially fabricated cylindrical compact specimens were used equipped with two thermocouples at strategic locations. The porosity of these specimens was also measured.The estimated effective thermal conductivities of various Mn-Al compacts were in the range of 5.5 to 10.5 W m−1 °C−1, which are much lower than that of Al (237 W m−1 °C−1), and close to that of Mn (7.8 W m−1 °C−1). The effective thermal conductivities of Mn-Al powder compacts decreased with an increase in the compact's Mn composition and porosity. Within the examined temperature range of 250 to 600 °C, the effect of temperature on the effective thermal conductivity was minimal. A purely theoretically derived prediction of Mn-Al compact thermal conductivity is substantially higher than the estimates of using the IHTP.

scholarly journals Determination of Radiative Thermal Conductivity in Needlepunched Nonwovens

2008 ◽  
Vol 3 (4) ◽  
pp. 155892500800300 ◽  
Author(s):  
Rahul Vallabh ◽  
Pamela Banks-Lee ◽  
Massoud Mohammadi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Extinction Coefficient ◽  
Dominant Mode ◽  
Hot Plate ◽  
Guarded Hot Plate ◽  
Ftir Spectrometer ◽  
Radiative Thermal Conductivity

Radiation heat transfer is found to be the dominant mode of heat transfer at temperatures higher than 400–500K [11]. Convection heat transfer being negligible in nonwovens, effective thermal conductivity is given by the sum of its conduction and radiation components. In this research two methods were identified to determine radiative thermal conductivity of needlepunched samples made from Nomex fibers. The first method involved the determination of radiative thermal conductivity using effective (total) thermal conductivity determined using a Guarded Hot Plate (GHP) instrument. In the second method radiative thermal conductivity was estimated using the extinction coefficient of samples. The extinction coefficient was determined by using direct transmission measurements made using a Fourier Transform InfraRed (FTIR) spectrometer. Results confirmed that radiation was the dominant mode of heat transfer at temperatures higher than 535 K. The conduction component of effective thermal conductivity did not change much in the range of densities tested. Empirical models for predicting the temperature difference across thickness of the fabric and the radiative thermal conductivity with R-square values of 0.94 and 0.88 respectively showed that fabric density, fabric thickness, fiber fineness, fiber length, mean pore size and applied temperature were found to have significant effect on the effective thermal conductivity and its radiation component. Though a high correlation between the results of Method 1 (Guarded Hot Plate) and Method 2 (FTIR) was not seen, the absorbance measurements made using the FTIR spectrometer were found to have significant effect on the radiative thermal conductivity.

Thermal Analysis of Heat-Generating Pools Bounded From Below by Curved Surfaces

1994 ◽  
Vol 116 (1) ◽  
pp. 127-135 ◽  
Author(s):  
M. J. Tan ◽  
D. H. Cho ◽  
F. B. Cheung
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Thermal Analysis ◽  
Effective Thermal Conductivity ◽  
Experimental Studies ◽  
Computer Code ◽  
Energy Sources ◽  
Curved Surfaces ◽  
Melt Pool

A computer code that features the use of a directional effective thermal conductivity in modeling natural convection in heat-generating pools has been developed to analyze heat transfer in such pools, which are bounded from below by curved surfaces. Illustrative calculations pertaining to two published experimental studies on convective heat transfer in water pools with uniformly distributed volumetric energy sources are carried out using the code. The water pools used in the two studies under consideration were cooled either from the top or from the bottom, but not from both. The utility as well as the limitations of the effective thermal conductivity approach in the context of addressing the issue of melt-pool coolability is demonstrated by comparisons of calculated results with the experimental data.

Determination of the effective thermal conductivity of the porous media based on digital rock physics

Geothermics ◽  
2021 ◽  
Vol 97 ◽  
pp. 102267
Author(s):  
Du Dongxing ◽  
Zhang Xu ◽  
Wan Chunhao ◽  
Liu Jiaqi ◽  
Shen Yinjie ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Porous Media ◽  
Effective Thermal Conductivity ◽  
Rock Physics ◽  
Digital Rock Physics ◽  
Digital Rock
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