Image-based method for evaluation of effective thermal conductivity of metal foam with hollow ligaments

Abstract

A feature preserving image-based method was used to estimate the effective thermal conductivity of copper metal foam having hollow ligaments. Hollow portions of the ligament and node were identified from X-ray computed microtomography images, through image processing. The effective thermal conductivity was estimated for foams with hollow ligaments filled with water, air, or vacuum. The fluid filling the pore was considered as water or air. Estimations were also conducted for the case where the metal foam is kept in a vacuum condition, where the heat transfer happens only through the ligaments and nodes. The effective thermal conductivity of metal foam with hollow ligaments was compared with that of metal foams with solid ligaments, maintaining the same ligament cross-sectional area. Two metal foams, having total porosity of 90.8% and 90% and hollowness of 4.45% and 1.65% respectively, were selected for the study. The effective thermal conductivity values obtained were compared with the analytical and empirical models available in the literature. Microtomography-based computational fluid dynamics study was also conducted based on the three-dimensional replica of the metal foam, generated from the two-dimensional tomography images. The thermal conductivity obtained from the computational microtomography based study and the image-based method was found to be in good agreement.