Metal Foam Layer Research Articles

Improving the Melting Duration of a PV/PCM System Integrated with Different Metal Foam Configurations for Thermal Energy Management.

The melting duration in the photovoltaic/phase-change material (PV/PCM) system is a crucial parameter for thermal energy management such that its improvement can realize better energy management in respect to thermal storage capabilities, thermal conditions, and the lifespan of PV modules. An innovative and efficient technique for improving the melting duration is the inclusion of an exterior metal foam layer in the PV/PCM system. For detailed investigations of utilizing different metal foam configurations in terms of their convective heat transfer coefficients, the present paper proposes a newly developed mathematical model for the PV/PCM–metal foam assembly that can readily be implemented with a wide range of operating conditions. Both computational fluid dynamic (CFD) and experimental validations proved the good accuracy of the proposed model for further applications. The present research found that the average PV cell temperature can be reduced by about 12 °C with a corresponding improvement in PCM melting duration of 127%. The addition of the metal foam is more effective at low solar radiation, ambient temperatures far below the PCM solidus temperature, and high wind speeds in nonlinear extension. With increasing of tilt angle, the PCM melting duration is linearly decreased by an average value of (13.4–25.0)% when the metal foam convective heat transfer coefficient is changed in the range of (0.5–20) W/m2.K. The present research also shows that the PCM thickness has a positive linear effect on the PCM melting duration, however, modifying the metal foam configuration from 0.5 to 20 W/m2.K has an effect on the PCM melting duration in such a way that the average PCM melting duration is doubled. This confirms the effectiveness of the inclusion of metal foam in the PV/PCM system.

Natural Convection in Annulus Between Two Concentric Cylinders Partially Filled with Metal Foam Distributed with New Suggested Design

The investigation of natural convection in an annular space between two concentric cylinders partially filled with metal foam is introduced numerically. The metal foam is inserted with a new suggested design that includes the distribution of metal foam in the annular space, not only in the redial direction, but also with the angular direction. Temperatures of inner and outer cylinders are maintained at constant value in which inner cylinder temperature is higher than the outer one. Naiver Stokes equation with Boussinesq approximation is used for fluid regime while Brinkman-Forchheimer Darcy model used for metal foam. In addition, the local thermal equilibrium condition in the energy equation of the porous media is presumed to be applicable for the present investigation. CFD ANSYS FLUENT software package (version 18.2) is used as a solver to this problem. Various parameters are examined; Rayleigh number, Darcy number, and thermal conductivity ratio to study the effect of them on fluid flow and heat transfer inside the annuli space in the suggested design of metal foam layer. current model is compared with the available published results and good agreement is noticed. Results showed that as Rayleigh number increases the dominated of convection mode increases and Nusselt increases. Also, Nusselt is larger at the higher Darcy and thermal conductivity ratio. It was found that at Rayleigh of 106 and thermal conductivity ratio of 104 Nusselt reach its higher value which is 6.69 for Darcy of 0.1 and 6.77 for Darcy of 0.001. A comparison between this design and the traditional design was established for Darcy 0.001 and thermal conductivity ratio 102, and its showed a good enhancement in Nusselt number and the greatest enhancement percentage was 44% at Rayleigh equal 5*104 while the lowest percentage is 6% for Rayleigh equal106.

Thermal Energy Storage and Heat Transfer of Nano-Enhanced Phase Change Material (NePCM) in a Shell and Tube Thermal Energy Storage (TES) Unit with a Partial Layer of Eccentric Copper Foam.

Thermal energy storage units conventionally have the drawback of slow charging response. Thus, heat transfer enhancement techniques are required to reduce charging time. Using nanoadditives is a promising approach to enhance the heat transfer and energy storage response time of materials that store heat by undergoing a reversible phase change, so-called phase change materials. In the present study, a combination of such materials enhanced with the addition of nanometer-scale graphene oxide particles (called nano-enhanced phase change materials) and a layer of a copper foam is proposed to improve the thermal performance of a shell-and-tube latent heat thermal energy storage (LHTES) unit filled with capric acid. Both graphene oxide and copper nanoparticles were tested as the nanometer-scale additives. A geometrically nonuniform layer of copper foam was placed over the hot tube inside the unit. The metal foam layer can improve heat transfer with an increase of the composite thermal conductivity. However, it suppressed the natural convection flows and could reduce heat transfer in the molten regions. Thus, a metal foam layer with a nonuniform shape can maximize thermal conductivity in conduction-dominant regions and minimize its adverse impacts on natural convection flows. The heat transfer was modeled using partial differential equations for conservations of momentum and heat. The finite element method was used to solve the partial differential equations. A backward differential formula was used to control the accuracy and convergence of the solution automatically. Mesh adaptation was applied to increase the mesh resolution at the interface between phases and improve the quality and stability of the solution. The impact of the eccentricity and porosity of the metal foam layer and the volume fraction of nanoparticles on the energy storage and the thermal performance of the LHTES unit was addressed. The layer of the metal foam notably improves the response time of the LHTES unit, and a 10% eccentricity of the porous layer toward the bottom improved the response time of the LHTES unit by 50%. The presence of nanoadditives could reduce the response time (melting time) of the LHTES unit by 12%, and copper nanoparticles were slightly better than graphene oxide particles in terms of heat transfer enhancement. The design parameters of the eccentricity, porosity, and volume fraction of nanoparticles had minimal impact on the thermal energy storage capacity of the LHTES unit, while their impact on the melting time (response time) was significant. Thus, a combination of the enhancement method could practically reduce the thermal charging time of an LHTES unit without a significant increase in its size.

Phase-Transition Thermal Charging of a Channel-Shape Thermal Energy Storage Unit: Taguchi Optimization Approach and Copper Foam Inserts.

Thermal energy storage is a technique that has the potential to contribute to future energy grids to reduce fluctuations in supply from renewable energy sources. The principle of energy storage is to drive an endothermic phase change when excess energy is available and to allow the phase change to reverse and release heat when energy demand exceeds supply. Unwanted charge leakage and low heat transfer rates can limit the effectiveness of the units, but both of these problems can be mitigated by incorporating a metal foam into the design of the storage unit. This study demonstrates the benefits of adding copper foam into a thermal energy storage unit based on capric acid enhanced by copper nanoparticles. The volume fraction of nanoparticles and the location and porosity of the foam were optimized using the Taguchi approach to minimize the charge leakage expected from simulations. Placing the foam layer at the bottom of the unit with the maximum possible height and minimum porosity led to the lowest charge time. The optimum concentration of nanoparticles was found to be 4 vol.%, while the maximu possible concentration was 6 vol.%. The use of an optimized design of the enclosure and the optimum fraction of nanoparticles led to a predicted charging time for the unit that was approximately 58% shorter than that of the worst design. A sensitivity analysis shows that the height of the foam layer and its porosity are the dominant variables, and the location of the porous layer and volume fraction of nanoparticles are of secondary importance. Therefore, a well-designed location and size of a metal foam layer could be used to improve the charging speed of thermal energy storage units significantly. In such designs, the porosity and the placement-location of the foam should be considered more strongly than other factors.

Efficient thermal management of the photovoltaic/phase change material system with innovative exterior metal-foam layer

This research proposes an innovative configuration for modifying the thermal management system of the photovoltaic (PV) panel, integrated with a phase-change material (PCM) with an attached exterior metal-foam layer to the rear part of the PCM container. The configuration enables faster heat dissipation from the system leading to longer thermal-management duration for the PV panel during the energy storage (PCM charging) mode. Also, it supports faster energy recovery (PCM discharging) rate by decreasing the amount of heat trapped in the melted part of the PCM during the solidification mode. The effects of the foam-layer inclusion, PCM thickness, and PV tilt angle are numerically simulated and revealed. A mathematical model that accounts for natural convection effects of the melted PCM and non-Darcy effects of the metal foam, is formulated and validated via previous experiments. The results show that inclusion of an exterior foam layer could increase the PCM melting time, and the corresponding PV thermal-management duration, by up to 32% and 55% respectively, depending on the PCM thickness and PV tilt angle. The results also show that reducing the tilt angle from 90° to 30° increases the melting time by about 18%. Thus, a superior PCM-based thermal management is achieved. Moreover, utilizing PCM of thickness in the range of 20–30 mm lengthens the melting time by up to 54%, enhancing the potential for improved thermal management of PV panels.

Experimental study of partially metal foam wrapped tube bundles

Overall heat transfer and pressure drop for three novel staggered tube banks with tubes partially wrapped with metal foam layers have been experimentally studied in an open circuit wind tunnel. The positions of the metal foam layers around the tubes are different in the studied tube banks, TB1, TB2, and TB3. In other words, the angles between inlet flow direction and metal foam layers placement around the tubes are 0, ±45, and ±90° in TB1, TB2, and TB3, respectively. The most interesting result of the present study is that heat transfer and pressure drop are closely related to the position of the porous layers around the tubes and the thermal performance augmentation could be achieved by selecting suitable positions for metal foam layers. The results indicate that the tube bank in which metal foam layers are centered at 0 and 180° from the front stagnation point of tubes (TB1) exhibits a better heat transfer performance at the same pressure drop comparing with TB2 and TB3. To illustrate this, at about 7 Pa, TB1 disposes of 62% and 82% more heat than TB2 and TB3, respectively.

Enhancement of heat transfer from a horizontal cylinder wrapped with whole and segmented layers of metal foam

In the present study, the flow and heat transfer characteristics from a horizontal cylinder in crossflow wrapped with whole and segmented layers of metal foams are investigated. High porosity and thermal conductivity metal foam layers are tested with two different thicknesses. The horizontal cylinders are heated with a uniform heat flux and forced convection tests are conducted for Reynolds number range of 7500 – 18000. The angle at which the metal foam segmented layers are positioned against the incoming flow is varied to study the effect of the angle of incidence on the performance. The heat transfer coefficient and pressure drop are measured in order to determine the overall performance factor which relates the enhancement in heat transfer with the pressure drop augmentation. The experimental results showed that all metal foam configurations outperformed the bare cylinder case. The whole layer configuration showed the highest heat transfer enhancement as opposed to the segmented layer case, but with a higher pressure drop. However, the segmented metal foam layer configuration, at an optimum angle of incidence, provided the best heat transfer enhancement with a lower pressure drop, signifying the highest overall performance factor.

A bio-inspired, low pressure drop liquid cooling system for high-power IGBT modules for EV/HEV applications

Thermal management of high power density insulated gate bipolar transistors (IGBTs) using a low pumping power is crucial for the development of high-performance electric vehicles (EVs) and hybrid electric vehicles (HEVs). In the present work, the liquid cooling module inspired by a human respiratory system was developed to provide enhanced thermohydraulic performance. The suggested cooling module consists of a multiscale flow manifold connected to a metal foam layer bonded to the bottom substrate of IGBT module. The unique flow path uniformly distributes the coolant to multiple IGBTs with minimizing the required pumping power, while maximizing the heat exchange area. The porosity of the metal foam was determined considering the conflict between the conductive and convective heat flux. The developed cooling module was applied to the single IGBT module, including 6 IGBT/diode pairs generating 1.55 kW of heat. The proposed cooling module provided a low (0.2 K/W) thermal resistance using only ~2 kPa of the pressure drop that is approximately 10 and 100 times lower than that of previously reported turbulator and microchannel systems, respectively. Even when the number of IGBT/diode pairs is increased from 6 to 24 (single to quadruple IGBT modules), only ~8 kPa of the pressure drop was required, which shows the high scalability of the proposed solution. This work will help develop a compact, low pumping power cooling solution for high-performance EV/HEV applications.

Thermohydraulic analysis of hybrid nanofluid in a multilayered copper foam heat sink employing local thermal non-equilibrium condition: Optimization of layers thickness

In the present study, fluid flow and heat transfer characteristics of a heat sink partially fitted with multilayered porous medium are analyzed. The multilayered copper foam contains three different layers placed at the bottom wall of the heat sink exposing to a uniform heat flux. The whole occupied volume of the porous region is 60% of the channel. The main objective of the current study is to reveal a layout for the porous medium with optimum thickness for each layer in two proposed models to maximize the heat transfer and minimize the pressure drop. In the constant particle diameter model, all three layers have an equal particle diameter of 1.5 cm with three porosities of 0.95, 0.85 and 0.75 from bottom to top. In the constant porosity model, all three layers have an equal porosity of 0.95 with three particle diameters of 0.5, 1 and 1.5 cm from bottom to top. To trade-off between the desirable (heat transfer) and undesirable (pressure drop) outcomes, the dimensionless number of performance evaluation criterion (PEC) is determined. Darcy–Brinkman–Forchheimer and local thermal non-equilibrium (LTNE) models are applied to solve the governing equations in the porous region. The CFD numerical simulations are conducted to analyze the effect of each layer thickness of the multilayered porous medium in the two proposed models on the thermohydraulic parameters such as friction coefficient, Nusselt number and PEC number. At the optimum layouts of the porous medium, water-graphene nanoplatelet/platinum hybrid nanofluid is applied to enhance the thermal performance of the heat sink. The obtained results reveal that the highest PEC number is achieved in the constant porosity model equal to 1.17 at the case in which the lower, middle and upper metal foam layer thicknesses are 0.6, 1 and 0.2 cm, respectively, resulting in 145% heat transfer enhancement. In constant particle diameter model, the highest PEC number equals to 1.26 at the case in which the lower, middle and upper metal foam layer thicknesses are 1, 0.6 and 0.2 cm, respectively, resulting in 191% heat transfer augmentation compared with the plain channel. Further increase in PEC number is observed by adding nanoparticles to the base fluid for nanofluid volume concentration of 0.1% in constant porosity and particle diameter models which are equal to 1.22 and 1.31, respectively.

Transient phase change heat transfer in a metal foam-phase change material heatsink subject to a pulse heat flux

Abstract In the present study, the effect of using a layer of metal foam in a composite metal foam – phase change heatsink is addressed. The bottom of the heatsink is subjected to a pulse heat flux, while the top of the heatsink is exposed to an external cooling convective flow. The melting/solidification of the Phase Change Materials (PCMs) is modeled using the enthalpy porosity approach. The partial differential equations governing the natural convective flow and the heat transfer in the clear flow region and porous layers of the heatsink are introduced and transformed into a non-dimensional form using non-dimensional variables. The Finite Element Method (FEM) with an automatic time-step and grid adaptation is employed to solve the governing equations. The model and the numerical code are validated by comparison to several results obtained in recent works available in the literature. The effect of the surrounding heat transfer by convection and the fusion temperature of the PCM on the heatsink performance and on the phase change behavior is investigated. The results show that melting heat transfer occurs during the activation of the pulse heat flux while the solidification commences with a small delay after the pulse heat flux turns off. The heatsink presents a major benefit when the external cooling power is weak. Moreover, a heatsink with a lower fusion temperature shows a better cooling efficiency. The presence of a metal foam layer notably improves the cooling efficiency of the heatsink. However, the location of the porous layer shows a minimal effect on the heatsink efficiency.

Liquid cooling module incorporating a metal foam and fin hybrid structure for high power insulated gate bipolar transistors (IGBTs)

We propose a liquid cooling system incorporating a porous medium combined to the multiscale flow manifold. Specifically, this work compares two types of porous media by varying the porosity: the first type only includes a metal foam layer, and the second incorporates an additional circular pin-fin array within the metal foam. The thermohydraulic performances of each type such as the average junction temperature, temperature deviation, flow were investigated using both numerical and experimental approaches. Due to the influence of the additional thermal conductivity matrix by fin structure integration, the second configuration (metal-foam and pin-fin hybrid type) provides a higher thermal performance compared to the first one. The suggested cooling solution with the second configuration could provide a very low thermal resistance (~0.185 K/W) with the pressure drop range between 5 and 15 kPa, which surpasses the performances of the previous-reported direct liquid cooling solutions such as the jet impingement, turbulator, and microchannel. This work will help develop high performance and compact cooling solutions for high power semiconductor applications such as an insulated gate bipolar transistor (IGBT) or a microprocessor.

Scale-integrated simulation of coupled radiation and convection in metal foam layer under high-flux irradiation

Coupled radiation-convection heat transfer inside a unit metal foam layer with high-flux irradiation is studied using improved scale-integrated simulation. It integrates the discrete-scale CFD simulation with that of continuum-scale via the multi-domain concept with thermal radiation effect considered. Conservations of mass flux and energy are satisfied on these specified subdomain interfaces, and a special defined transition zone with geometry-dependent functional quantities is introduced within the continuum-scale subdomain. This zone is adjacent to the discrete-scale subdomain which ensures a reasonable transition. Absorbed radiative fluxes and radiative heat transfer within the whole domain are calculated with Monte Carlo method and treated as heat sources. The problem under consideration has been investigated via the discrete-scale simulation, the continuum-scale simulation, and the scale-integrated simulation. The accurateness of scale-integrated simulation has been fully validated for predicting both flow field and heat transfer characteristics in comparison with the outcomes of discrete-scale simulation and other investigations. Deviations between the outcomes of continuum-scale simulation and discrete-scale simulation are found to be mainly caused by inconsistent local absorbed radiative heat fluxes distribution and impinging effect around the entry region. Up to 70% and 60% reduction of computation time and memory footprints are achieved when scale-integrated strategy is employed for the CFD simulation compared with the discrete-scale simulation. Meanwhile, the detailed fluctuated characteristics of the local concerned region and overall heat transfer performance can be precisely reflected. It may break up the computation limitations of the discrete-scale simulation in studying the energy transport process in foam based solar receiver applications.

Effective thermal conductivity of high porosity open-cell metal foams

In this paper, a model for effective thermal conductivity of high porosity open-cell metal foams is developed by assuming the foam morphology as 3D tetradecahedron structure. The effective thermal conductivity of metal foams is first studied using the numerical simulation method, which the geometrical model (the ratio of the edge length of node to the radius of ligament) is calibrated with the experimental data. The geometrical model is divided into four distinctive layers along the heat transfer direction. The effective thermal conductivity of four layers is then determined by fitting the numerical results. Consequently, the model for effective thermal conductivity of metal foams is proposed based on the Fourier law. Several other analytical models and the experimental data are used to verify the effectiveness of the present model. The results show that the present model can be satisfactorily accurate to calculate the effective thermal conductivity of metal foam by considering the ratio of the edge length of node to the radius of ligament as a second order polynomial function of the porosity. The effective thermal conductivity of each layer is related to the porosity of each layer and overall porosity of metal foam. Compared with the experimental data, the present model has high accuracy with relative RMS deviation of less than 10%. The finding of this study can help guide the thermal design of porous media.

X-ray tomography and modelling study on the mechanical behaviour and performance of metal foam flow-fields for polymer electrolyte fuel cells

Porous metal foams have been used as alternative flow-fields in proton exchange membrane fuel cells (PEMFCs), exhibiting improved performance compared to conventional ‘land and channel’ designs. In the current work, the mechanical behaviour of PEMFCs using metal foam flow-fields is investigated across different length scales using a combination of electrochemical testing, X-ray computed tomography (CT), compression tests, and finite element analysis (FEA) numerical modelling.Fuel cell peak power was seen to improve by 42% when foam compression was increased from 20% to 70% due to a reduction in the interfacial contact resistance between the foam and GDL. X-ray CT scans at varying compression levels reveal high levels of interaction between the metal foam and gas diffusion layer (GDL), with foam ligaments penetrating over 50% of the GDL thickness under 25% cell compression. The interfacial contact area between the foam and GDL were seen to be 10 times higher than between the foam and a stainless-steel plate. Modelling results demonstrate highly uniform contact pressure distribution across the cell due to plastic deformation of the foam. The effect of stack over-tightening and operating conditions are investigated, demonstrating only small changes in load distribution when paired with a suitable sealing gasket material.

Numerical Simulations of Fluid Flow and Heat Transfer through Aluminum and Copper Metal Foam Heat Exchanger – A Comparative Study

This article discusses about a numerical simulation of a metal foam heat exchanger system carried out by a commercial software. A metal foam layer is attached to the bottom of the heat exchanger to absorb heat from the exhaust hot gas leaving the system. Two types of metal foams with two different pores per inch (PPI) values are considered for heat transfer enhancement. Similarly, two different materials Aluminum and copper, that poses high thermal conductivity, metal foams are considered for the present numerical simulations. The heat exchanger system is simulated over a range of 6–30 m/s fluid velocity. The proposed simulations are compared with theoretical and experimental data available in the literature. The goal is to improve the thermal performance of the heat exchanger by decreasing the pressure drop and maximizing the heat transfer rate. Finally, it has been noticed that the velocity of the fluid decreases as PPI increases at the expense of its pressure drop. The copper metal foam gives a maximum increase of 4–10% heat transfer rate compared to aluminum metal foams for a fluid velocity of 30 m/s.

Experimental investigation of heat transfer of flowing liquid film with inserted metal foam layer subjected to air jet impingement

In this paper, coupling the air jet impingement and the copper metal foam above flowing liquid film were employed to enhance the heat transfer. The thickness of flowing liquid film can be controlled owing to the application of the metal foam above the film, and its solid matrix extends the air-liquid-solid interface of heating surface. The evaporated water can be supplied by the capillary force in the porous layer. The experiments were conducted to investigate the performances of the flowing liquid film with inserted porous layer subjected to impinging jet air. The air jet velocity, the flow rate and thicknesses of the liquid film as well as the porosity of metal foam influence the surface temperature of heated wall and the corresponding local heat transfer coefficient greatly. The change ratios of heat transfer coefficient due to the above factors were presented. More cooling can be obtained on the heated wall in the flowing liquid film with inserted porous layer subjected to impinging jet air while the higher liquid film velocity and air jet velocity, the thinner liquid film and the lower porosity of metal foam occur.

Thermal hydraulic performance of micro-channel heat sink with composite metal foam-solid fin design

<p indent="0mm">Three-dimensional (3D) interconnect technology promises significant performance advantages for the next generation of high speed and multi-functional electronic devices, however, the large-scale integration of electronic circuit and vertical stacking of multi-functional dice have been demonstrated to result in substantially increased waste-heat generation rates and localized hotspots. Efficient thermal management solutions are imperative to ensure the operating temperature of components below a reasonable level. Among various cooling techniques, metal foam heat sink has been identified as a promising alternative for electronic cooling, because of the large specific surface area, high effective thermal conductivity and intensive fluid mixing capability that foam material provided. In this study, a novel micro-channel heat sink with combined metal foam-solid fin, namely combined fin heat sink (CFHS), was established for electronics cooling. Numerical simulations based on Brinkman-Darcy extended momentum equation and local thermal non-equilibrium energy equations were carried out to investigate the fluid flow and heat transfer characteristics. To simplify the computations, a single channel was used as the computational domain with a dimension of 20 mm×2.4 mm× <sc>6 mm.</sc> The constant heat flux of <sc>100 W/cm²</sc> was supplied at the bottom wall to simulate the high-powered electronic device. Metal foam and fin were made of high thermal conductivity copper, and pure water was used as the working coolant. It was assumed that the metal foam was fully saturated with fluid in laminar flow state and the thermal resistance between the metal foam and fin was neglected. Effects of combined fin configuration on the flow and heat transfer performances were studied to determine the optimal porosity and dimensionless metal foam layer thickness for designing the CFHS. The thermal performance of the novel heat sink was compared to that of the conventional heat sink, and the total thermal resistance was analyzed based on the simplified thermal resistance network. The results indicate that the CFHS is more favorable in promoting thermal performance that the average Nusselt number of CFHS is 2.53 times higher than that of the conventional heat sink, while accompanied by the high pressure drop as a penalty. The flow resistance and specific area are two conflicting parameters that affect the thermal and hydraulic performances of the CFHS, our results show that there exists a critical dimensionless metal foam thickness and optimal porosity, which are 0.9 and 0.3, respectively. Compared with the conventional heat sink, the total thermal resistance of CFHS is significantly reduced by 56%, and the thermal performance factor of CFHS performs 1.32 times higher. The presented CFHS thus provides a feasible solution for thermal management of electronic devices with high-powered density.

Simulation and Optimization of Metal-foam Tube Banks for Heat Transfer Enhancement of Exhaust Heat Exchangers

An essential issue of waste heat recovery (WHR) from engine’s exhaust gas, which could be effectively purified by modern after-treatment techniques, is the development of high-efficient, compact and lightweight high-temperature gas heat exchanger. Due to its multi-functional advantages, open-cell metal foam shows promising potentials in gas heat transfer enhancement. Thus, it is meaningful to explore the feasibility of this novel structure’s application on engine exhaust gas, by replacing bulky structures outside tubes with metal foam layers. In this paper, the heat transfer enhancement of forced convection in metal foam-wrapped tube banks was numerically studied. The Darcy-Forchheimer-Brinkman momentum model considering viscous loss and inertial loss, and the local thermal non-equilibrium energy model which considers the interstitial heat transfer between fluid and solid were employed for the porous zone. Effects of foam thickness and free stream velocity were analyzed to examine the heat transfer and pressure drop characteristics. A comparative analysis was also conducted with a bare tube bank. Results showed that the heat transfer performance of metal foam tube bank can enhance 1.8 to 2.0 times, measured in terms of the area goodness factor. In an array with fixed foam thickness, the better heat transfer performance is obtained at lower free stream velocities. It was also found that, within the designated fluid velocity range, tube banks with thicker foam layers show higher heat transfer rates and larger pressure drops as well. However, there exists an optimal dimensionless thickness of foam layer at 0.15 which gives the highest area goodness factor for the configuration considered in this study.

Partially metal foam wrapped tube bundle as a novel generation of air cooled heat exchangers

Heat transfer and pressure drop for a tube bank with 5 rows of tubes wrapped by metal foam layers has been numerically studied. The results show that covering the tubes with a thin metal foam layer could result in substantial heat transfer enhancement in comparison to the bare tube bank. Moreover, it is indicated that metal foam wrapped tube banks could be considered as an effective alternative to finned tube banks because of their better performance. Pressure drop could be regarded as the main drawback of the metal foam wrapped tube banks. Therefore, introducing some new arrangements in which the tubes are partially covered by the foam layer is the most interesting results of the present study. By means of a new arrangement, approximately the same Nusselt number can be achieved compared to the fully wrapped tubes and at the same time the pressure drop reduces by 60%, area goodness factor increases by 33% and the amount of the foam usage decreases by 50% with respect to the fully wrapped foam tubes. This result would be extremely important for designing industrial heat exchangers with higher effectiveness and lower costs. It seems that these new arrangements can lead to the design of a new generation of air cooled heat exchangers.

Thermal Performance Analysis of Biporous Metal Foam Heat Sink

The present study presents a concept of biporous metal foam heat sink applicable to electronic cooling. This heat sink has two metal foam layers arranged in parallel along the primary flow direction, with different metal foam thickness, porosity, and pore density for each layer. The forced convective heat transfer in biporous metal foam heat sink is numerically investigated by employing the Forchheimer–Brinkman extended Darcy momentum equation and local thermal nonequilibrium energy equation. The effects of geometrical and morphological parameters on thermal and hydraulic performance are discussed in detail, and the heat transfer enhancement mechanism of biporous metal foam is analyzed. The thermal performance of biporous metal foam heat sink is compared with that of uniform metal foam heat sink. The results show that the thermal resistance of the biporous metal foam heat sink decreases with decrease of top layer metal foam porosity at a fixed bottom metal foam porosity of 0.9. It is seen that the biporous metal foam heat sink can outperform the uniform metal foam heat sink with a proper selection of foam geometrical and morphological parameters, which is attributed to the presence of high velocity gradient at the boundary layer that can enhance the convective heat transfer. The best observed thermal performance of biporous metal foam heat sink is achieved by employing 30 pores per inch (PPI) metal foam at the bottom layer, with a fixed 50 PPI metal foam at the top layer for the porosities of both layers equal to 0.9, and the optimal thickness of the bottom foam layer is about 1 mm.