| Summary: | Open-cell porous metals and alloys, based on polymer foam replication techniques, have been performing significantly well and, in many cases, replacing traditional porous metals, including metal foams, in various applications because of their unique properties and structural features including high porosity, semi-uniform structure, light weight and high surface to volume ratio. In applications requiring flow of fluids (gas, liquid or both) through open-cell porous structures, for instance in multi-stage filters, heat exchangers, water purification and the storage and transfer of liquid, pressure-drop and flow characteristics of the fluid are essential parameters in application design and performance. Despite the fact that pressure-drop is often sought to be minimised, high pressure-drop is sometimes required such as when used as abradable seals in jet engines. In this work, the structure of Inconel 625, open-cell porous metals (with nominal cell sizes 450, 580, 800 and 1200 pm) were studied in detail using a series of imaging and morphological techniques. The effect of airflow velocity, in the range of 0-70 m s'1, on the pressure-drop characteristics for bulk and structurally tailored, diffusion bonded, multilayered, open-cell porous structures, as a function of thickness (affected by sectioning), density (affected by compression) and structural alterations (affected by multi-pore sized insets, porous metal stacking and air gaps), were thoroughly investigated. As the air flow velocity increases, fluid properties tend to change and drag force increases in comparison with the viscous effect causing the pressure drop data to deviate from the nonlinear, quadratic Forchheimer model into a cubic equation at a velocity value higher than 20 m s'1. The need for accurate pinpointing of the different regimes (Darcy, Forchheimer and Turbulent), which enables precise determination of the permeability (K) and form drag coefficient (C), was highlighted. Understanding the pressure-drop behaviour for multilayered, open cell porous structures will offer the possibility for combining layers with different porosities and pore sizes giving the ability to tailor the structure to achieve bespoke flow conditions for demanding applications. For example, the use of a 9 mm thick porous structure in three different configurations (bulk, stacked and gapped) causes the pressure-drop to change drastically, while having the same weight (3.38g), thus, the potential for mass-efficient porous structures is readily achievable.
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