Abstract

This study experimentally investigates the impact of low pore density and thickness on the flow resistivity, hence permeability, of periodic open porous materials. An experimental setup is developed to measure the flow resistivity of porous samples adhering to the guidelines provided by the International Standards Organization 9053 and American Society for Testing and Materials C522 standards. The flow resistivity of three different porous microlattices is considered. Two of the three lattices are obtained from a monospherical void subtraction method, while the third is the octet-truss lattice. The monospherical void geometries are body-centered-cubic and A15 lattices. The pore density, measured in terms of pores-per-inch (PPI), was varied from 1 PPI to 12 PPI for all three microlattices considered. At low PPIs, the pore sizes are on the order of macroscale thickness. Hence, the volume-averaging or homogenized equivalent fluid model may not be valid. The thickness variation for a fixed PPI is also considered over limits where traditional volume-averaging methods break down. It is shown that at extremely low PPIs and thicknesses, entrance and exit losses become dominant, and the flow resistivity measured as per standards ceases to be a constant with PPI or thickness. Furthermore, existing two-dimensional modeling approaches for losses due to flow in pipes are adopted to predict the entry and exit pressure loss coefficients for the considered microlattices with appropriate modifications.

Highlights

  • The pressure drop resulting from fluid flow through porous materials is an important parameter to monitor and optimize in many applications such as heat sinks,1 heat exchangers, catalysts, and filters.2,3 The static airflow resistivity “σ” is a measure of viscous drag losses that depend on the microstructural geometry of porous materials.4 It is used to establish correlations between the structure of porous materials and acoustical properties such as absorption and attenuation.5Flow resistivity may be measured using an experimental setup developed based on the American Society for Testing and Materials (ASTM) C5225 and International Standards Organization (ISO) 9053 (1991)6 standards

  • The flow resistivity for A15, body-centered cubic (BCC), and octet microlattices of various pore densities was measured using the apparatus described in Sec

  • Three different unit cell configurations, viz., BCC, A15, and octet-truss, are designed, fabricated, and tested using a custom-developed flow resistivity setup adhering to ISO 9053 and ASTM C522 standards

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Summary

Introduction

The pressure drop resulting from fluid flow through porous materials is an important parameter to monitor and optimize in many applications such as heat sinks, heat exchangers, catalysts, and filters.. Flow resistivity may be measured using an experimental setup developed based on the American Society for Testing and Materials (ASTM) C5225 and International Standards Organization (ISO) 9053 (1991) standards. In this method, the flow velocity V and the pressure drop ΔP across the porous sample of length L foam are measured within the Darcy flow regime. The pressure drop ΔP for flow through porous media in the Darcy regime is given by Eq (1) and is valid when the fluid flow velocity is sufficiently small: ΔP μ

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