Investigation of the Relationship between Morphology and Thermal Conductivity of Powder Metallurgically Prepared Aluminium Foams.

Arun Gopinathan,Jaroslav Kováčik,Tomáš Dvorák,Jaroslav Jerz

doi:10.3390/ma14133623

Abstract

Among different promising solutions, coupling closed-cell aluminium foam composite panels prepared by a powder metallurgical method with pore walls interconnected by microcracks, with low thermal conductivity phase change materials (PCMs), is one of the effective ways of increasing thermal conductivity for better performance of thermal storage systems in buildings. The internal structure of the foam formation, related to the porosity which decides the heat transfer rate, plays a significant role in the thermal energy storage performance. The dependence of the heat transfer characteristics on the internal foam structure is studied numerically in this work. The foamable precursor of 99.7% pure aluminium powder mixed with 0.15 wt.% of foaming agent, TiH2 powder, was prepared by compacting, and extruded to a volume of 20 × 40 × 5 mm. Two aluminium foam samples of 40 × 40 × 5 mm were examined with apparent densities of 0.7415 g/cm3 and 1.62375 g/cm3. The internal porous structure of the aluminium foam samples was modelled using X-ray tomography slices through image processing techniques for finite element analysis. The obtained numerical results for the heat transfer rate and effective thermal conductivity of the developed surrogate models revealed the influence of porosity, struts, and the presence of pore walls in determining the heat flow in the internal structure of the foam. Additionally, it was found that the pore size and its distribution determine the uniform heat flow rate in the entire foamed structure. The numerical data were then validated against the analytical predictions of thermal conductivity based on various correlations. It has been found that the simplified models of Bruggemann and Russell and the parallel–series model can predict the excellent effective thermal conductivity results of the foam throughout the porosity range. The optimal internal foam structure was studied to explore the possibilities of using aluminium foam for PCM-based thermal storage applications.

Highlights

Porous metallic structures with interconnected pores are a promising solution for enhancing the thermal conductivity of the phase change materials in TES applications [1]
Effective thermal conductivity mainly refers to when a significant role is played by diffusion, and it controls the energy transport
By analysing the X-ray tomography images of the foam, no pores of definite shape were found, and pore wall ruptures were visible in both samples

Summary

Introduction

Porous metallic structures with interconnected pores are a promising solution for enhancing the thermal conductivity of the phase change materials in TES applications [1]. The foam structure is useful for various applications such as thermal transfer enhancement, insulation in buildings, etc Such metal matrix composites with their high thermal conductivity to the coefficient of thermal expansion ratio bring the interest among many researchers to utilize in the building and various sectors where the need for better thermal performance arises [3]. The parameters of the microstructure inside the foam and the properties of those porous structures are related qualitatively in most of the previous studies [5,6] In all these studies, porosity is dealt with as the significant parameter influencing the porous structure’s thermal conductivity, and most of the empirical equations are based on porosity [6,7]. Apart from porosity, pore strut influence on thermal conductivity and the micropore effect are studied [7,8]

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Results

Discussion

Conclusion