Open-cell Porous Metals Research Articles

Analytical fin efficiency model for open-cell porous metal fins based on Kelvin cell assumption

Open-cell porous metals are widely used to enhance convective heat transfer of thermal management devices. In this paper, the open-cell porous metal structure was represented by a polyhedron model known as the Kelvin cell, and an analytical model for the efficiency of the porous metal fin attached to an isothermal surface was derived. The forced convective heat transfer coupled with heat conduction through the ligaments of porous metal was analyzed to derive the fin efficiency model. The effects of pore diameter, ligament diameter, and porous metal fin height on the fin efficiency and heat transfer rate of porous metal fins were also investigated. The new analytical fin efficiency model based on the Kelvin cell was compared with the fin efficiency evaluated using computational fluid dynamics analysis results; good agreement was found. The proposed analytical fin efficiency model avoids the numerical calculations required for heat transfer analysis of porous metals used as extended surfaces in many engineering applications such as heat sinks and heat exchangers, and can produce simple but effective results.

Analytical Fin Efficiency Model for Open-Cell Porous Metal Fins Based on Kelvin Cell Assumption

Analytical Fin Efficiency Model for Open-Cell Porous Metal Fins Based on Kelvin Cell Assumption

Energy Absorption of Additively Manufactured Porous Metals with Disordered Cells

Lightweight porous metals are focused on as energy absorbing materials for automobiles. Open-cell porous metals were manufactured through additive manufacturing process. Their cell structures were designed based on Voronoi diagrams using a commercial 3D-CAD software. Both ordered and disordered cell structures with the same porosities were successfully designed in this study. Compression tests and explicit finite element analysis revealed heterogeneous deformation behaviors in ordered porous metals. On the other hand, the porous metals with disordered cell structure showed relatively isotropic and uniform deformation, which is suitable as energy absorbing materials. Controlling the disordered cell structure designed by 3D-Voronoi diagram enables to develop the advanced porous metals having various mechanical properties.

Experimental and numerical analysis of thermal flow in open-cell porous metal during Darcy-Forchheimer transition regime

A numerical analysis of pressure drop and heat transfer for open-cell porous media is performed using a three-dimensional conjugate heat transfer model. Porous metal with a pore density of 20 pores per inch (PPI) and porosity of 95.7% is used in the present numerical simulation. Real microstructure of the open-cell porous metal is constructed using stacked images obtained by X-ray computed tomography method. Computed thermal-fluid characteristics are compared directly with the experimental pressure drop and unit overall thermal resistance values. The flow through porous metal can be divided into the Darcy regime and the Forchheimer regime. The thermo-fluidic characteristics in the Darcy regime and the Forchheimer regime are investigated numerically. The flow separation is not observed in the Darcy regime, but the wake region occurs in the Forchheimer regime because of the flow separation on the ligament surface. The contribution of the total drag acting on the walls (top & bottom) is very small, namely, less than 5% compared to the total drag on ligaments. The total drag force coefficient of ligaments tends to converge at high Reynolds number. This is because the pressure drag force is dominant due to the wake effect in the Forchheimer regime. Local Nusselt number is large near the upstream side of the ligament and very low in the wake region. Average Nusselt number increases with Reynolds number. In the Forchheimer regime, wakes developed behind ligaments increase the pressure loss and decrease the heat transfer performance.

Experimental comparison of optical properties of nanofluid and metal foam for using in direct absorption solar collectors

Open-cell porous metal foams and nanofluids are among the solar absorbers for radiation absorption in solar collectors. The optical properties of absorbers have an important role in the thermal performance of direct and volumetric absorption solar collectors. In the present work, porous foam and nanofluid are made from the same materials and their optical properties are measured experimentally. The spectrophotometric experiments are performed on the produced porous metal foams and water based nanofluids from two materials namely SiC and CuO. In water-saturated porous foams, the effect of porosity (90% and 95%), pore diameter (10PPI-30PPI) and type of material (CuO and SiC) are survived while the influence of volume fraction and kind of nanoparticles in water based nanofluids are examined. Obtained results indicate that in SiC and CuO nanofluids, by increasing concentration from 0.01 vol% to 0.1 vol%, extinction coefficient increases by 20% and 176%, respectively. Moreover, the extinction coefficient in porous foams increases by decreasing the porosity and pore diameter. Comparing the results of nanofluid with porous foam of the same material shows that there is no significant difference in extinction coefficient for CuO nanofluid (0.1 vol%) and CuO porous foam (90%, 30PPI) while the extinction coefficient of SiC porous foam (90%, 20PPI) is 4 times higher than its nanofluid (0.1 vol%).

Investigations on a hybrid element with cellular metallic material for heating, cooling and ventilation

Surface heating and cooling systems are gaining more and more importance in building energy technology. In order to implement these systems not only on the floor but also on the ceilings and walls, the thermodynamic requirements are supplemented by constructional requirements. In order to fulfil these requirements, the use of open-cell porous metals for such systems will be investigated in more detail. In addition to the design and manufacturing challenges, a large number of numerical and experimental investigations on test samples are also necessary. These investigations are described and explained in more detail in the following article.

Evaluation of Local Strain Distribution during Compressive Deformation of Open-Cell Porous Metals

Relationship between the macroscopic and local strains of porous metals is examined by microstructural observation. Open-cell porous titanium with 60% porosity was compressed up to 30% macroscopic strain at room temperature. Open-cell porous nickel with 95% porosity was compressed up to 40% macroscopic strain at room temperature. Local strains in cell walls of both porous titanium and nickel were evaluated by electron backscatter diffraction (EBSD). Absolute value of the local strain increased with increasing the macroscopic strain and it is smaller than that of macroscopic strain. In addition, the value of the local strain at the cell junctions was larger than that of the center of cell struts.

Influence of Porosity on Mechanical Behavior of Porous Cu Fabricated via De-Alloying of Cu–Fe Alloy

We report on a study of the mechanical behavior of porous Cu containing micron-sized pores and fabricated by de-alloying of a Cu–Fe precursor alloy. Our results show that the minimum volume fraction of pores that can be obtained by using an approach that involves de-alloying of a Cu–Fe precursor alloy is approximately 40 vol%. Moreover, the average pore size formed by de-alloying Cu–Fe of varying compositions is in the range of 1.5–4.0 μm. Our mechanical behavior results reveal that the yield stress increases from 3.9 to 58.6 MPa as the volume fraction of porosity decreases from 78.9% to 39.3%. Moreover, our data shows that the influence of porosity on the relative yield stress and relative Young’s modulus conforms to the scaling equations of Gibson and Ashby as formulated for open-cell porous metals. The pore cell characteristics and deformation modes of porous Cu produced by de-alloying Cu–Fe alloys were discussed in the context of the observed fluctuations in the value of the constants C and n in the Gibson-Ashby scaling equation. The evolution of microstructure during compressive deformation of porous Cu was studied and the results reveal an increase in the fraction of low-angle grain boundaries, an increase in the number of twins and a decrease in the average grain size with increasing strain from 0% to 70%.

Measurement of tortuosity of porous Cu using a diffusion diaphragm cell

Open-cell porous metals have many potential applications, such as heat exchangers and flow batteries, due to good permeability for fluid flow. Porous metals manufactured by space holder methods have controllable porous structure, but the fluid pathways and channels are tortuous. The tortuosity can directly influence the fluid permeability and turbulence, which in turn affect the performance of the porous metal. This paper measured the tortuosity of porous Cu, manufactured by Lost Carbonate Sintering (LCS), directly by a diffusion method using a diaphragm cell. The tortuosity of the samples with pore sizes 250–1500µm and porosities 0.56–0.84 was in the range of 1.33–1.78. It decreased with porosity and increased with pore size. The measured values were comparable to those reported in literature, obtained by the acoustic absorption method.

Mass Transfer Performance of Porous Nickel Manufactured by Lost Carbonate Sintering Process

Open cell porous metals are excellent electrode materials due to their unique electrochemical properties. However, very little research has been conducted to date on the mass transport of porous metals manufactured by the space holder methods, which have distinctive porous structures. This paper measures the mass transfer coefficient of porous nickel manufactured by the Lost Carbonate Sintering process. For porous nickel samples with a porosity of 0.55–0.75 and a pore size of 250–1500 μm measured at an electrolyte flow velocity of 1–12 cm s−1, the mass transfer coefficient is in the range of 0.0007–0.014 cm s−1, which is up to seven times higher than that of a solid nickel plate electrode. The mass transfer coefficient increases with pore size but decreases with porosity. The porous nickel has Sherwood numbers considerably higher than the other nickel electrodes reported in the literature, due to its high real surface area and its tortuous porous structure, which promotes turbulent flow.

Numerical Simulation of Heat Transfer in Porous Metals for Cooling Applications

Porous metals have low densities and novel physical, mechanical, thermal, electrical, and acoustic properties. Hence, they have attracted a large amount of interest over the last few decades. One of their applications is for thermal management in the electronics industry because of their fluid permeability and thermal conductivity. The heat transfer capability is achieved by the interaction between the internal channels within the porous metal and the coolant flowing through them. This paper studies the fluid flow and heat transfer in open-cell porous metals manufactured by space holder methods by numerical simulation using software ANSYS Fluent. A 3D geometric model of the porous structure was created based on the face-centered-cubic arrangement of spheres linked by cylinders. This model allows for different combinations of pore parameters including a wide range of porosity (50 to 80 pct), pore size (400 to 1000 µm), and metal particle size (10 to 75 µm). In this study, water was used as the coolant and copper was selected as the metal matrix. The flow rate was varied in the Darcian and Forchheimer’s regimes. The permeability, form drag coefficient, and heat transfer coefficient were calculated under a range of conditions. The numerical results showed that permeability increased whereas the form drag coefficient decreased with porosity. Both permeability and form drag coefficient increased with pore size. Increasing flow rate and decreasing porosity led to better heat transfer performance.

Open-cell porous metals for thermal management applications: fluid flow and heat transfer

Open-cell porous metals for thermal management applications: fluid flow and heat transfer

Experimental investigation of the convective heat transfer coefficient for open-cell porous metal fins at low Reynolds numbers

The heat transfer characteristics and convective heat transfer coefficient of porous metal fin are experimentally investigated. The pore density of the porous metal fin and frontal velocity of the working fluid are varied in the range of 20, 40, and 80 pores per inch, and 0.007–0.17m/s, respectively. The porous metal fins are fabricated from nickel with different porosities and various pore densities. The geometrical parameters of the test samples are measured using an optical method. In this study, porous metals are considered as a fin and the heat transfer performances are experimentally evaluated. An equivalent diameter based on the permeability and porosity is used as the characteristic length to calculate the Reynolds numbers and Nusselt numbers. When the equivalent diameter is used as the characteristic length, the measured Nusselt numbers converge to a single curve regardless of the pore density. The Nusselt number variation appears to be very similar to previous correlations developed for convective heat transfers of turbulent pipe flows. Consequently, an empirical correlation of the Nusselt number for porous metal fins is proposed in the form of a Dittus–Boelter correlation.

Specific surface areas of porous Cu manufactured by Lost Carbonate Sintering: Measurements by quantitative stereology and cyclic voltammetry

Open-cell porous metals have many applications due to high surface area to volume ratios. Porous metals manufactured by the space holder methods have distinctively different porous structure from commercial open-cell metal foams, but very little research has been conducted to characterise the surface area of this class of materials. This paper measured the geometric, electroactive and real surface areas of porous Cu samples manufactured by the Lost Carbonate Sintering process by quantitative stereology and cyclic voltammetry. A cyclic voltammetry (peak current) procedure has been developed and successfully applied to the measurement of electroactive surface areas of the porous Cu. For porous Cu samples with pore sizes 75–1500 μm and porosities 0.5–0.8, the volumetric and gravimetric specific geometric, electroactive and real surface areas are in the ranges of 15–90 cm−1 and 5–45 cm2/g, 200–400 cm−1 and 40–130 cm2/g, and 1000–2500 cm−1 and 400–800 cm2/g, respectively, varying with pore size and porosity. The geometric, electroactive and real surface areas are found to result from the contributions from primary porosity, primary and secondary porosities, and surfaces of metal particles, respectively. The measurement methods adopted in this study can provide vital information of surface areas at different length scales, which is important for many applications.

326 高気孔率を有するオープンセル多孔質の開発

326 高気孔率を有するオープンセル多孔質の開発

Thermal Properties of Porous Copper Manufactured by Lost Carbonate Sintering

Active cooling techniques are often required to achieve high rates of heat dissipation in thermal management applications. Open-cell porous metals are good candidates for use as heat exchangers. This paper studies the fluid transport and thermal properties of porous copper samples with different pore structures manufactured using the LCS method. The results showed that the permeability increases with porosity but decreases with pore size. The thermal conductivity increases with relative density according to the power law. The effects of porosity and pore size on the heat transfer performance of the porous copper samples are significant, due to their effects on the permeability and thermal conductivity. For the porous copper samples with double-layer structures, the permeability follows the rule of mixture and the heat transfer coefficient can be predicted by a recently developed segment model.

Properties of open-cell porous metals and alloys for orthopaedic applications

One shortcoming of metals and alloys used to fabricate various components of orthopaedic systems, such as the femoral stem of a total hip joint replacement and the tibial plate of a total knee joint replacement, is well-recognized. This is that the material modulus of elasticity (E') is substantially larger than that of the contiguous cancellous bone, a consequence of which is stress shielding which, in turn, has been postulated to be implicated in a cascade of events that culminates in the principal life-limiting phenomenon of these systems, namely, aseptic loosening. Thus, over the years, a host of research programs have focused on the synthesis of metallic biomaterials whose E' can be tailored to match that of cancellous bone. The present work is a review of the extant large volume of literature on these materials, which are called open-cell porous metals/alloys (or, sometimes, metal foams or cellular materials). As such, its range is wide, covering myriad aspects such as production methods, characterization studies, in vitro evaluations, and in vivo performance. The review also includes discussion of seven areas for future research, such as parametric studies of the influence of an assortment of process variables (such as the space holder material and the laser power in the space holder method and the laser-engineered net-shaping process, respectively) on various properties (notably, permeability, fatigue strength, and corrosion resistance) of a given porous metal/alloy, innovative methods of determining fatigue strength, and modeling of corrosion behavior.

卑・半金属およびそれらの合金によるオープンセル型ポーラス材料の開発

卑・半金属およびそれらの合金によるオープンセル型ポーラス材料の開発

Foam Heat Exchangers: A Technology Assessment

Open-cell porous metal foams have received attention for use in compact heat exchangers due to their increasing availability and improved thermal performance. In recent years, considerable research has been conducted on use of metallic and nonmetallic foams to further improve performance of state-of-the-art heat exchangers. In this paper, we report preliminary results from fabrication, development and experimental investigation of thermal-hydraulic performance of high-temperature metal foam heat exchangers for automotive exhaust gas recirculation (EGR) system. A brief review of nickel–chromium and stainless-steel foam heat exchanger technology and of recent efforts on their manufacturing techniques for a liquid-to-air heat exchange application is presented. Measured heat transfer and pressure drop data for foam heat exchangers and their comparison with performance of a conventional wavy plate-fin heat exchanger are discussed. Technical challenges and risks associated with foam heat exchangers are discussed, along with recommendations for future development.