Impact of the Backbone Connectivity on the Gas Pressure-Dependent Thermal Conductivity of Porous Solids

It has been shown that structural properties of open porous solids, such as the mean pore size, can be derived from gas pressure-dependent thermal conductivity data. However, a reliable prediction of the total thermal conductivity of a porous sample with complex backbone structure from structural da...

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Bibliographic Details
Published in:International journal of thermophysics 2022, Vol.43 (1), Article 8
Main Authors: Swimm, K., Vidi, S., Reichenauer, G., Ebert, H.-P.
Format: Article
Language:English
Subjects:
Aerogels
Backbone
Classical Mechanics
Compression tests
Condensed Matter Physics
Conductivity
Connectivity
Finite difference method
Gas pressure
Geophysics
Heat conductivity
Heat transfer
Industrial Chemistry/Chemical Engineering
Melamine
Melamine formaldehyde resins
Physical Chemistry
Physics
Physics and Astronomy
Pore size
Porous materials
Pressure dependence
Thermal conductivity
Thermal coupling
Thermodynamics
Tortuosity
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Summary:It has been shown that structural properties of open porous solids, such as the mean pore size, can be derived from gas pressure-dependent thermal conductivity data. However, a reliable prediction of the total thermal conductivity of a porous sample with complex backbone structure from structural data is not possible, because the degree of coupling of gaseous and solid thermal conduction is hard to estimate. To explore the impact of structural effects, the thermal performance of different model structures, generally characteristic for porous solids (necks, dead ends, tortuosity), was theoretically evaluated by means of finite-difference calculations. As a result, we find that dead ends cause the highest amount of thermal coupling. On the other hand, independent experimental investigations were performed to support the theoretical findings. That means, the gas pressure-dependent thermal conductivities of two sample systems in a nitrogen atmosphere were analyzed: At first, thermal conductivity data for three organic, resorcinol–formaldehyde based aerogels with different structural properties were received from hot-wire measurements. Secondly, the regular cell structure of melamine resin foam was systematically changed by uniaxial compression within a guarded hot plate apparatus prior to determining the resulting thermal conductivity in the direction of compression. Overall, the measured gas pressure-dependent thermal conductivities of both systems indicate that the connectivity of the solid network significantly affects the solid–gas coupling term in porous solids. Both the experimental and theoretical results show that the coupling term decreases with increasing connectivity of the backbone material of a porous solid.
ISSN:0195-928X
1572-9567
DOI:10.1007/s10765-021-02936-4