Abstract

Metallic foams have diverse industrial applications due to their unique properties such as high porosity and high surface to volume ratio. To improve and modify the design of such applications, understanding of the foam characteristics such as unit pressure drop is required. Because of the complex microstructure of metallic foams, it is difficult to predict their characteristics by mathematical modeling analysis. Therefore, experimental studies have been suggested to discover the effect of microstructure on the pressure drop of metallic foams. Wide range of metallic foams having different thicknesses (2 to 63 mm), densities (83 to 91%), and pore sizes (0.4 to 2.3 mm) were tested in the present study. The unit pressure drop of same grade foam having different thicknesses was found to reduce with increasing the thickness. This effect results in different Darcian and non-Darcian permeability coefficients for the same foam which is unexpected, because these properties should be thickness independent and constant for each material. Consequently, experiments were conducted to validate that the pressure drop can be divided into two components of bulk and entrance pressure drops and found that, bulk contribution can be normalized by the thickness; however, entrance contribution cannot. After a certain thickness, which depends on the foam microstructure, the entrance contribution becomes constant. It was also observed that, entrance effect contributes more to the pressure drop for thin samples and at high velocities. Tests were also performed to non-destructively examine the homogeneity of the metallic foams and found that, heterogeneity can be detected if it is either located at the foam sides or inside the foam but with pores finer than the bulk foam