Foam Porosity Research Articles

Numerical Analysis of the Thermal Performance of a Hybrid Heat Sink Comprised of Perforated Foam Fins Embedded Within a Phase Change Material

ABSTRACTThis study presented a numerical model to evaluate a novel design of a hybrid heat sink incorporating perforated foam fins (PFFs) instead of solid fins (SFs) within a phase change material (PCM). This innovation is designed to enhance thermal performance in electronic cooling applications. The base of the heat sink was subjected to constant heat fluxes of 2, 3, and 4 kW/m2. The effect of the perforation location (top, center, and bottom) within the foam fin and foam porosities (0.85, 0.90, and 0.95) were investigated. The results showed that the hybrid PFF design demonstrably improved thermal efficiency compared to the SF configuration. This innovative approach offered three benefits: a significant reduction in overall heat sink weight, an augmentation of the thermal conductivity of PCM, and the intermixed molten PCM between the fins passages through perforations. The PFF heat sink extended the operational time by 6%–8% for the range of heat fluxes at SPT of 70°C and led to a 24.5% increase in PCM volume, compared to the SF configuration. Complete melting of the PCM in the PFF heat sink is observed at 29 min for the highest heat flux of 4 kW/m2, while the melting rates are 25% and 62% for the applied heat flux of 2 and 3 kW/m2. Perforation location within the foam fin (top, center, and bottom) achieved equivalent heat transfer capabilities, enabling design flexibility for perforation location. The PFF with a porosity of 0.85 demonstrated superior thermal performance.

High temperature in-situ 3D monitor of microstructure evolution and heat transfer performance of metal foam

Metal foams with excellent mechanical properties and low effective thermal conductivity (ETC) are widely used in high-temperature components. The 3D microstructure evolution under high-temperature loading is complex. The deformation mode and ETC at high temperature of metal foams are determined by the microstructure at different stress and the parent material properties. In this paper, high-temperature in-situ micro X-ray computed tomography (μ-CT) compressive test was performed to monitor the 3D microstructure evolution and failure mechanism of closed-cell Al foams at 300 ℃. High-fidelity material twin models were then generated from the in-situ μ-CT scans under various high-temperature loadings to calculate the corresponding ETC of the foams. The effects of the applied strain and corresponding 3D microstructure on the ETC were discussed based on experimental and simulation results. The results reveal that the 3D porosity and ETC evolution of foam compressed at 300 °C are bilinear. A compressive strain of 30 % was identified as a critical strain, beyond which both porosity and ETC change dramatically with increasing strain. Finally, a theoretical model based on the Kelvin tetrakaidecahedron was developed to reveal the effect of microstructure evolution caused by compressive strain on the ETC of foams.

Optimizing graphite-enhanced composite PCMs for superior thermal transport in shell and tube latent heat storage systems

Latent heat thermal energy storage (LHTES) systems are designed to store excess thermal energy, addressing supply-demand mismatches during periods of low supply. Integrating such systems in the field is challenging due to the slow charging caused by the low thermal conductivity of phase change materials (PCM). This shortfall can be mitigated using composite PCM (CPCM) as the thermal storage medium, consisting of form-stable porous graphite foam impregnated with PCM. Compressed expanded graphite (CEG) is one such easily accessible form-stable porous material. The graphite foam in the CPCM causes a significant improvement in the effective thermal conductivity of the storage medium; however, it causes reduced latent heat storage capacity. Existing literature on CPCM mainly emphasizes positive aspects like enhanced thermal conductivity and reduced melting time while overlooking the adverse impact on latent heat storage capacity. This trade-off must be addressed while designing such a system, particularly when the storage unit is of fixed size and shape. This study aims to find the optimal volumetric proportion of CEG in CPCM, striking the best balance between these two conflicting attributes. Objective parameters such as energy storage ratio (ESR) and capacity ratio (CR) are introduced, along with charging duration, and they are optimized based on control parameters like CEG foam porosity (ε), HTF inlet temperature (Tin), and flow Reynolds number (Re). The analysis, obtained from a volume-averaged numerical model, involves diffusion-dominated energy transfer in the CPCM domain and provides crucial design guidelines for fixed-geometry LHTES units with CPCM as the storage medium.

Multi-objective optimization of metal foam parameters for enhanced performance of LHTES unit in shell-and-tube configurations

Latent heat thermal energy storage (LHTES) units utilize phase change materials (PCMs) to effectively store thermal energy and address the challenges of solar energy intermittency and instability. Heat transfer characteristics largely influence the thermofluidic efficiency of the LHTES unit during phase transitions. To improve the typically low heat transfer capabilities of PCMs, high-conductivity metal foams are introduced to enhance bulk heat conduction. This study focuses on optimizing the parameters of composite PCM (CPCM) embedded in the LHTES unit, specifically examining metal foam height (H), angle (θ), and porosity (ϵ), primarily affecting the performance of the CPCM. A series of Taguchi-based orthogonal experiments were conducted to analyze the effects of these variables. The results indicate that metal foam height has a notable influence on the CPCM performance, significantly reducing melt fraction variations caused by changes in cross-sectional geometry. ANOVA analysis shows that the metal foam height contributes 49.02% to improve operational time and 73.62% to enhance melt fraction. The study also identifies the optimal values for the metal foam parameters (H, θ, ϵ) that most effectively improve the LHTES unit thermal performance. Based on various indices, an economic assessment of the optimal configuration further supports the proposed design. Overall, the findings provide a recommended configuration to enhance the LHTES unit performance, contributing valuable insights for developing efficient TES systems and supporting sustainable energy management.

Waste-to-resource: Employing lime mud as a foaming agent in glass foam manufacturing

The paper industry globally releases vast amounts of lime mud waste annually, raising environmental concerns. Composed mainly of calcium carbonate, lime mud has been utilized in various research works, including catalyst synthesis, cement production, and ceramic fabrication. This study investigates the use of lime mud as an eco-friendly foaming additive in the production of glass foam. Glass foams were prepared through a simple sintering method, utilizing glass cullet collected from households and incorporating different lime mud contents (0.5–2.0 wt%). The effects of lime mud concentration on the density, porosity, and pore size distribution of the glass foams were examined. Additionally, the thermal conductivity, compressive strength, and Weibull modulus were investigated in relation to the average porosity. The results revealed that the pore size distribution was dependent on the amount of lime mud, exhibiting three distinct distributions: a positively skewed distribution, a non-symmetric bimodal distribution, and a positively skewed distribution with a wide range. The Weibull modulus markedly decreased with increasing pore size. The compressive strength of the prepared glass foams ranged from 5.53±0.40–12.73±0.46 MPa, while the bulk density and porosity fell within the ranges of 0.41±0.02–0.70±0.04 g/cm3 and 72.12±1.45–85.38±0.98 %, respectively. The thermal conductivity could be as low as 0.07 W/m·K, approaching the upper limit for commercial glass foams used in thermal energy storage systems and meeting the requirements for Type I cellular glass thermal insulation classified by ASTM C552–16.

Structure-property relationships of polydisperse open-cell foams: Application to melamine foams

The melamine foam presents a unique microstructure characterized by an interconnected network of solid struts, which form the edges and faces of high porosity open cells. This study investigates the influence of pore size distribution on acoustic properties for three commercially available melamine foams. Based on the measured transport parameters, a top-down approach is employed to determine the equivalent Kelvin-cell size corresponding to each transport parameter. The differences found in these equivalent pore sizes indicate that the mono-size model is not suitable for these materials, a difference from which a quantitative estimate of the level of polydispersity can be deduced (using macro-scale information). The polydispersity was confirmed from experimental evidence at micro-scale from the analysis of SEM images. Moreover, the measurements collected at micro-scale (average pore size and its standard deviation) can be used as input data to determine the transport and sound absorbing behavior of melamine foam samples from structure-property relationships available for open cell microstructures. This work provides evidence that the polydispersity of melamine foams should be taken into account to obtain an accurate and consistent picture of microstructure and transport properties of such open cell high porosity foams.

Polycaprolactone-based shape memory foams as self-fitting vaginal stents

There is an urgent critical need for a patient-forward vaginal stent that can prevent debilitating vaginal stenosis that occurs after pelvic radiation treatments and vaginal reconstruction. To this end, we developed a self-fitting vaginal stent based on a shape-memory polymer (SMP) foam that can assume a secondary, compressed shape for ease of deployment. Upon insertion, the change in temperature and hydration initiates foam expansion to shape fit to the individual patient and restore the lumen of the stent to allow egress of vaginal secretions. To achieve rapid actuation at physiological temperature, we investigated the effect of architecture of two photocurable, polycaprolactone (PCL) macromers. Star-PCL-tetraacrylate displayed a reduced melting temperature as compared to a linear-PCL-diacrylate. Upon fabrication into high porosity foams with emulsion-templating, both compositions displayed shape fixity (>90 %) in a crimped, temporary shape. However, only the PCL star-foams displayed shape recovery (∼84 %) at 37 °C with expansion back to its permanent shape. A custom mold and curing system were then used to fabricate the PCL star-foams into hollow, cylindrical stents. The stent was crimped to its temporary insertion shape (50 % reduction in diameter, OD ∼ 11 mm) with a custom radial crimper and displayed excellent shape fixity for deployment (> 95 %) and shape recovery (∼ 100 %). To screen vaginal stents, we developed a custom benchtop pelvic model that simulated vaginal anatomy, temperatures, and pressures with an associated computational model. The crimped SMP vaginal stent was deployed in the model and expanded to walls of the canal (∼70 % increase in cross-sectional area) in less than 5 min after irrigation with warm water. The vaginal stent demonstrated retention of vaginal caliber with less than 10 % decrease in cross-sectional area under physiological pressures. Collectively, this work demonstrates the potential for SMP foams as self-fitting vaginal stents to prevent stenosis and provides new open-source tools for the iterative design of other gynecological devices. Statement of significanceVaginal stenosis, a painful narrowing of the vaginal canal, is a common complication after pelvic radiation therapy or reconstructive surgery. To address this clinical need, we have created a self-fitting vaginal stent from a shape-memory polymer foam. The stent compresses for easy insertion and then expands to adapt to each patient's anatomy to maintain an open vaginal canal and prevent stenosis. This innovative stent provides a patient-friendly solution that could make a significant difference for women undergoing pelvic treatments by reducing pain, aiding recovery, and improving quality of life.

Study on the Enhancement of Energy Storage Mechanism for Phase Change Materials by High Porosity Metal Foams: Numerical Simulation

Introduction: The findings of the study elucidated that as the porosity of copper foam diminished, the internal average temperature of the composite phase change material increased, concurrent with a reduction in the maximum average temperature differential and an enhancement in temperature homogeneity between the heating interface and the copper composite phase change material. Methods: Under the filling rate of this experiment, the heat transfer mechanism of copper composite phase change materials (CPCMs) was mainly heat conduction. Results: With the increase of porosity, the melting time of phase change materials shortened, and the change of natural convection ratio was more obvious. At the same melting time, the porosity decreased, and the pressure drop increased. Conclusion: When the porosity was 94 % and 96 %, the pressure drop was 1425.34 Pa/m and 1222.65 Pa/m, respectively, which was 37.01 % and 17.53 % higher than that when the porosity was 98 %.

The role of Voronoi catalytic porous foam in reactive flow for hydrogen production through steam methane reforming (SMR): A pore-scale investigation

Complex pore structures in catalysts can significantly impact flow, heat transfer, and ultimately, reaction efficiency. In steam methane reforming (SMR) for hydrogen production, replacing simple catalyst geometries with intricate, interconnected structures can enhance heat transfer and optimize the SMR process. Reactive flow in Voronoi catalytic foams (VCFs) with conjugate heat transfer is investigated using OpenFOAM for pore-scale simulations. The study examines the impact of porosity, pore density (PPI), PPI distribution (uniform vs. gradient), flow direction, inlet velocity, and temperature on hydrogen production rates within a selected representative elementary volume (REV). The results show that reducing the porosity of the simple foam from 0.8 to 0.6 has led to a 25% increase in the hydrogen production mass flow rate. Additionally, replacing the simple foam with a porosity of 0.6 with a gradient foam with the same porosity can improve the hydrogen production rate by 17%. Also, it is observed that the inlet velocity has a more significant effect on the hydrogen production rather than the inlet temperature, such that increasing the inlet velocity from 0.5 to 2 m/s results in a remarkable 75% increase in the hydrogen production rate.

Phase change heat storage and enhanced heat transfer based on metal foam under unsteady rotation conditions

Phase change heat storage technology is an essential method for balancing supply and demand in solar energy heat utilization. In this study, a numerical model of the phase change heat storage process is built to explore the impact of non-constant rotation, with and without metal foam. Subsequently, an investigation into the influence of metal foam pore density and porosity on heat storage performance is conducted, with a focus on Taguchi design for statistical analysis. The research delves into the effects of foam parameters on heat storage rate, temperature response, heat storage time, and heat storage properties. Findings reveal significant resolidification in the melting process of this thermal storage structure without metal foam, due to periodic rotation speed hindrance in transferring heat to the outside. Taguchi design results underscore the greater influence of porosity on the melting time and average heat storage rate compared to pore density. Specifically, a reduction in melting time by 62.21 % and 30.49 %, and an increase in average heat storage rate by 237.56 % and 51.19 % is observed when pore density and porosity are 40 PPI and 0.97, compared with the ones with porosities of 0.99 and 0.98, demonstrating minimal impact on total heat absorption.

Melting of PCM-graphite foam composites with contact thermal resistance: Pore-scale simulation

Latent heat energy storage systems have emerged as a solution to intermittency and instability in renewable energy sources, the phase transition of phase change materials (PCMs) within these systems is hindered by their poor thermal conductivity. Graphite foam, renowned for its superior thermal properties, stands as an ideal choice to improve the melting efficiency of PCMs. In the current study, the melting behavior of PCM-graphite foam composites is simulated by the pore-scale numerical simulation (PNS) by employing cubic idealized cells with spherical pores and cylindrical channels. The computed results demonstrate that the porosity and contact thermal resistance of graphite foam are key factors affecting the melting efficiency of PCMs. The full melting time (FMT) of PCMs increases with porosity, achieving a 53.1 % improvement as porosity decreases from 0.90 to 0.75. In addition, the absence of natural convection markedly diminishes the maximum melting rate of PCM, reducing it by 33.5 % to 50.3 % for porosity from 0.75 to 0.90. Notably, it needs to be emphasized that the melting rate of PCM is significantly reduced when the contact thermal resistance surpasses 1.0 × 10–4 m2·K·W−1. Compared to the idealized condition without contact thermal resistance, the dimensionless FMTs for porosities of 0.75, 0.80, 0.85, and 0.90 extend by 27.3 %, 27.1 %, 22.2 % and 23.9 % for a contact thermal resistance of 5.0 × 10–4 m2·K·W−1, respectively.

Embedded Fluidic Sensing and Control with Soft Open‐Cell Foams

AbstractThe synthesis of soft matter intelligence with circuit‐driven logic has enabled a new class of robots that perform complex tasks or conform to specialized form factors in unique ways that cannot be realized through conventional designs. Translating this hybrid approach to fluidic systems, the present work addresses the need for sheet‐based circuit materials by leveraging the innate porosity of foam—a soft material—to develop pneumatic components that support digital logic, mixed‐signal control, and analog force sensing in wearables and soft robots. Analytical tools and experimental techniques developed in this work serve to elucidate compressible gas flow through porous sheets, and to inform the design of centimeter‐sized foam resistors with fluidic resistances on the order of 109 Pa s m−3. When embedded inside soft robots and wearables, these resistors facilitate diverse functionalities spanning both sensing and control domains, including digital logic using textile logic gates, digital‐to‐analog signal conversion using ladder networks, and analog sensing of forces up to 40 N via compression‐induced changes in resistance. By combining features of both circuit‐based and materials‐based approaches, foam‐enabled fluidic circuits serve as a useful paradigm for future hybrid robotic architectures that fully embody the sensing and computing capabilities of soft fluidic materials.

Performance investigation of metal foam coupled to phase change material as coolant of photovoltaic concentrator systems: Optimization and electrical efficiency analysis

This research investigates the integration of graphitic metal foam with paraffin RT35HC to manage and reduce the temperature of PV cells, focusing on the rigorous examination of the synergistic effects of metal foam porosity and panel inclination on thermal management. A 2D numerical model was developed using ANSYS Fluent 14.0, where User-Defined Functions (UDFs) were employed to incorporate the Darcy-Brinkman-Forchheimer and Carman-Kozeny equations, accurately accounting for the effects of metal foam porosity on thermal conductivity and fluid flow resistance. Various foam porosities (ε = 0.80, 0.85, 0.90, 0.95, 1) were explored on both vertical and tilted panels across a spectrum of inclination angles (β= 0°, 30°, 45°, 75°, 90°). Results highlight critical parameters including PCM melting fraction, cell temperature evolution, and the resultant impact on solar cell electrical efficiency, both with and without metal foam. The integration of graphitic foam with RT35HC contributed to superior heat transfer and a marked reduction in cell temperature of the employed PV system by improving thermal conductivity and heat dissipation, particularly at slight inclination angles (β =0° to 30°), revealing a noteworthy enhancement in electrical efficiency ranging from 1.3 % to 3 %, respectively. Conversely, the absence of graphitic foam at steeper angles (β =45° to 90°) surprisingly strengthens the solar panel’s electrical performance. These findings provide valuable insights into the effects of metal foam integration at varying inclination angles, offering a pathway for the development of more efficient and reliable solar energy systems.

Effect of microstructure on the physicochemical characteristics of foam glass made by soda lime -CRT glasses and aluminium dross

Foam glass, an inorganic insulation material, is primarily manufactured from recycled glass or sand combined with a foaming agent. During fabrication, gas bubbles are generated in the softened glass, causing it to expand and form a cellular structure. Critical parameters such as cell size, type (closed or open cells), distribution, and uniformity significantly influence the physical and chemical properties of foam glass, ensuring sustained thermal efficiency. This research aims to produce foam glass exclusively from waste materials, thereby promoting the circular economy by utilizing container glass, cathode ray tube (CRT) glass, and aluminium dross. A comprehensive microstructural analysis, employing computer tomography and scanning electron microscopy, elucidated key properties including density, thermal conductivity, and water absorption. The manufactured foam glass exhibited lightweight characteristics, with a density ranging from 0.15 to 0.18 g/cm³. Additionally, the foam glass demonstrated low thermal conductivity (between 0.038 W/m·K and 0.05 W/m·K), which can be attributed to the heterogeneous distribution of cells that effectively reduce heat convection. This property makes foam glass an excellent thermal insulator. Furthermore, both high-absorption (open porosity) and low-absorption (closed porosity) foam glasses were successfully produced.

Numerical simulation of thermal performance of heat sink augmented with phase change material PCM integrated with solid and aluminum metal foam fins

AbstractThis study introduced a novel numerical modeling for the evaluation of a hybrid heat sink design by replacing the solid fins with aluminum foam fins (AFF) for the same thickness of 2 mm within a phase change material (PCM). This innovation is designed to enhance thermal performance in electronic cooling applications. Heat fluxes of 2, 3, and 4 kW/m2 were applied to the base. The performance has been verified at set point temperatures (SPT) of 60°C, 70°C, and 80°C, encompassing a range relevant to various applications. Different AFF thicknesses (4 and 6 mm) and foam porosities (0.85, 0.90, and 0.95) were investigated. The study demonstrated that AFFs improve heat transfer by increasing fin surface area and by effectively raising the thermal conductivity of the PCM. Compared to the SF heat sink, the results show that the AFF design extended the operational time by 5%–8% for the range of heat fluxes. Notably, AFFs with a thickness of 6 mm achieved a significant 41% improvement in the operation time at a lower SPT (60°C). The metal foam porosity of ε = 0.85 exhibited superior thermal performance within the investigated temperature range. This research paves the way for optimizing hybrid heat sink designs using metal foam for efficient thermal management and reduction of weight.

A study on syntactic aluminum foams manufactured infiltrating sintered preforms of iron hollow spheres

This work analyzes the microstructure, porosity, and mechanical properties of syntactic foams obtained infiltrating 3 mm in diameter Fe hollow spheres with an Al–12Si eutectic alloy. The hollow spheres were first sintered at 800, 900, and 1000 °C for 1h to obtain composite porous preforms, focusing on the effect of this sintering on the manufactured syntactic foams. Results showed that the increase in the sintering temperature led to an increase in the porosity from 51 to 56 %, also increasing the percentage of Fe in the solid part of the foams and decreasing the pore cell thickness. This led to significantly higher strength and a brittle behavior for the foams obtained using spheres sintered at 1000 °C, while the foams manufactured using lower temperatures presented a ductile behavior and lower mechanical properties. α (Al8Fe2Si) and β (Al5FeSi) were obtained during infiltration, decreasing the wall thickness of the Fe spheres.

Microstructure and performances of rigid polyurethane foam prepared using double‐effect baking powder as a foaming agent

AbstractThe preparation of rigid polyurethane foam with uniform pore size is extremely challenging. In this work, double‐effect baking powder was used as foaming agent, and rigid polyurethane foam with regular morphology was successfully prepared through semi‐prepolymerization. The rigid polyurethane foam apertures with regular morphology were controlled by the secondary release of CO2 when the content of baking powder is 0.30 part. Combined with theoretical calculation and experimental test, it is found that the particle size distribution, wall thickness, and hole shape are uniform, regular, thin, polygonal, and few broken holes. The compression strength, contact angle, and surface energy of the rigid polyurethane foam are 33.36 kPa, 109.6°, and 21.8 mJ/m2 after adding 0.20 part of double‐effect baking powder, respectively. By adjusting the amount of double‐acting baking powder, the porosity, mechanical properties and foam rate of the polyurethane foams could be significantly improved. Due to the molecular solvation effect, rigid polyurethane foams will deform in the water and oil due phase, but it can remain stable for a long time at room temperature without solvent. It provides a new method for the preparation of rigid polyurethane foam, which is expected to be widely used in transportation and other fields.Highlights Baking powder was firstly used as a foaming modifier for rigid polyurethane. Baking powder releases CO2 twice to ensure uniform structure of polyurethane cell. Rigid polyurethane foam has long‐term stability and regular, uniform cell holes. The porosity and mechanical properties of foams could be significantly improved. Foaming mechanism of rigid polyurethane using baking powder was firstly revealed.

Recycling coal overburden waste to fabricate functionally graded SiC foam with gradient microstructure via one step thermo-foaming process

An economical and efficient thermo-foaming method, coupled with an in-situ reaction bonding technique, was employed to produce mullite-bonded functionally graded silicon carbide (SiC) foams with gradient microstructures using coal mine overburden waste (CMW). The foaming process utilized sucrose dehydration with sulphuric acid, allowing for tailored porosity in SiC foams. Mullite bonding material was in situ developed during sintering, facilitated by silica and alumina from CMW, promoting mullite phase formation. Alumina incorporation further enhanced mullitization. The use of CMW as a low-cost precursor for mullite conversion facilitated SiC particle bonding through mullite, reducing sintering temperature and overall production cost. Varied sucrose content and sintering temperature influenced foaming behavior, porosity, microstructural gradient, and mechanical properties. Mullitization process, reaction bonding behavior, and mechanical properties were analyzed based on CMW and alumina content, and sintering temperature. The resulting SiC foams exhibited bulk density and porosity in the range of 0.6–1.2 g/cm3, 60–80 % respectively. This study introduces an eco-friendly approach for repurposing CMW waste and cost reduction in SiC foam manufacturing.

Experimental investigation on thermal performance of phase change materials–metal foam composites in ocean thermal engine

Because battery-powered underwater vehicles have limited long-term mission capacity, the development of ocean thermal engines that can harvest ocean thermal energy (OTE) is a potential solution to this “energy limitation” issue. Ocean thermal engines using solid-liquid phase change materials (PCM) for thermal–mechanical energy conversion. This study examined the effects of combining PCMs with metal foams (MF) on OTE harvesting. Two phase change materials and three MFs were considered. Experiments were conducted to measure the temperature change inside the PCM, phase change duration, and volume change to evaluate the thermal and energy-harvesting performances under different temperature and pressure conditions. Results show that(1) Mixed PCM composed of 95 % n-hexadecane and 5 % n-octane melting point decreased by 0.9–1.6 °C and volume change rate reduced by 16–40 % compared to pure n-hexadecane. (2) The mixed PCM has by 14–18 % higher output power than pure n-hexadecane. (3) Within the test range, to maximize the power density, the optimal porosity of copper foam and back pressure during melting were 94 % and 20 MPa, respectively. This study provides useful insights into the design and optimization of ocean thermal engines.

Performance improvement of novel latent thermal energy storage system with two-layer metal foam porosities

A 2D numerical analysis was conducted to examine the melting performance of a shell-and-tube-type phase change material with a two-layer copper foam having higher and lower porosity levels. The design parameters for these two layers of metal foam consisted of three different volume fill ratios (VFR) (30 %/70 %, 50 %/50 %, and 70 %/30 %) and three different shapes (circular, semi-circular, and elliptical) for the lower porosity layer. The results showed that a semicircular-shaped low porosity layer with a 30 % VFR had the least melting time of 475 s. When the VFR increased to 50 %, the elliptical and circular shapes had the least melting time of 394 s. However, at a VFR of 70 %, only the elliptical shape had the least melting time of 323 s. Furthermore, the results were compared with the uniform porosity metal foam system, and deduced that the two-layer system did not always have the lower melting time compared with that of the uniform porosity system because it depended on the VFR and shape of the different porosities filled in the different layers. Additionally, for an average porosity of the metal foam, an optimal combination of two different porosities was observed for the melting performance.