Heat Management Alternatives in Deep Underground Mines as a Crucial Part of Mine Ventilation

Abstract

The thermal transport properties of porous amorphous aluminosilicate structures are investigated using molecular dynamics simulations and finite element methods. This research aims to produce such aluminosilicate geofoam of desired thermal conductivity and use it as sprayable thermal insulation in deep mines or potentially in residential insulation applications. Aluminosilicates are naturally occurring minerals which have low thermal conductivity because of their high porosity. Since they are found in abundance in nature, they could be an economical alternative for the fabrication of thermal insulators used in the buildings and underground mines. The thermal and mechanical properties of the amorphous porous aluminosilicate structures (PAS) were studied during this research using computational and experimental methods. Molecular dynamics (MD) was used to characterize thermal properties and conductivity at the atomic level. Different Aluminum-Silicon ratios were studied in molecular dynamics to identify a suitable Al-Si ratio that would provide lowest possible thermal conductivity and high mechanical strength. The effect of density on thermal conductivity was also characterized. It was observed that thermal conductivity of the alumino silicate structure has a linear dependency on density. Also, for a particular given porosity, a larger distribution of smaller pores results in the aluminosilicate structure to have a lower thermal conductivity. This characteristic is related to the presence of more phonon scattering centers in highly porous systems thus causing a decrease in the mean free path of a phonon. The data obtained from the molecular dynamics simulations was used to physically fabricate the foams with similar densities in the laboratory and their associated thermal conductivity was experimentally measured. The molecular dynamics simulations and experimental data show a high degree of agreement with each other.The ultrasound non-destructive technique (NDT) was used to transmit wave energy to measure dynamic mechanical properties experimentally. This was performed for various different porosities of foams. The foam density was changed using different ratios of blowing agent and surfactant. The same was performed using the finite element method analysis in COMSOL Multiphysics platform for different sets of porosities. Acoustic and stress analysis was performed for different porosities to determine the P-wave and S-wave velocities and other elastic properties. A high-fidelity model of the foam was also generated using a micro-CT scan of the foam. Volume meshing was performed using Simpleware ScanIp software and was then transferred over to COMSOL to perform the modelling simulations. The data from different porosities obtained from these simulations agrees very well with the findings in the experimental analysis. The thermal conductivity values that have been obtained are seen to be a function of density of the material by transient plane source method. The mechanical properties have been characterized by Ultrasonic tests for macroscopic bulk specimens and techniques such as FEM at the Nanoscale and the results are hereby reported.