Dependence of thermal conductivity on structural parameters in porous samples

Abstract

The in-plane thermal conductivity of porous sintered bronze plates was studied both experimentally and numerically. We developed and validated an experimental setup, where the sample was placed in vacuum and heated while its time-dependent temperature field was measured with an infrared camera. The porosity and detailed three-dimensional structure of the samples were determined by X-ray microtomography. Lattice-Boltzmann simulations of thermal conductivity in the tomographic reconstructions of the samples were used to correct the contact area between bronze particles as determined by image analysis from the tomographic reconstructions. Small openings in the apparent contacts could not be detected with the imaging resolution used, and they caused an apparent thermal contact resistance between particles. With this correction included, the behavior of the measured thermal conductivity was successfully explained by an analytical expression, originally derived for regular structures, which involves three structural parameters of the porous structures. There was no simple relationship between heat conductivity and porosity.

On the effective thermal conductivity of aluminum metal foams: Review and improvement of the available empirical and analytical models

“…This model, Eq. (32), which considers the contribution of the only solid phase, provides good predictions when air is the working fluid but becomes inaccurate when the conductivity of the fluid phase is comparable to that of the solid. A similar relation was provided by Ma and Ye [71], in which the 1/3 term is replaced by a shape factor: this factor can be interpreted as the average of dimensionless temperature derivative weighted by volumes of cell walls [71].…”

“…At the moment, a significant effort is devoted to describing the foam structure in a more realistic way: from this perspective, X-ray computed microtomography (μ-CT) appears a promising and appealing approach to be coupled to numerical simulations. The literature includes several works dealing with μ-CT, not only limited to metal foams or thermal conductivity estimations [1,3,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. The literature offers a wide set of analytical and empirical correlations for the estimation of the effective thermal conductivity of metal foams.…”

Inhomogeneity in pore size appreciably lowering thermal conductivity for porous thermal insulators

“…From the microscopic viewpoint, the porous ceramic material can be simplified to a three-dimensional lattice of cubic cells and the interfacial thermal conductivity among the crystallites play a dominant role in affecting the overall thermal transport [15]. It was further experimentally confirmed that a higher interfacial thermal conductivity among the connected bronze particles would remarkably boost the thermal conductivity of sintered porous bronze materials [16]. Inspired by the abovementioned up-to-date observations, we could see a great limitation of thermal transport occurring in the materials system with inhomogeneous pore size, and thus we endeavor to reveal the underlying mechanisms for inhomogeneity in influencing the thermal transport and to design the universal porous materials with lower thermal conductivity.…”

Thermal Characterization of Innovative Sustainable Building Materials from Wool Textile Fibers Waste

“…The determination of the effective thermal conductivity of porous materials is very complex because it is dependent not only on the porosity, but also on the macroscopic structure of the materials. As a matter of fact, the way the solid components are connected developing a three-dimensional shape plays an important role [14]. The effective thermal conductivity of fibrous materials is the result of three modes of heat transfer: conduction in the solid and gaseous phase, convection in the gas, and radiation [15].…”