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An advanced numerical investigation has been carried out in order to study the effect of multiple injection strategies on Caterpillar heavy-duty diesel engine emissions. Both different injected fuel percentages for each pulse and several dwells between main and post phase were investigated via computational fluid dynamics (CFD) and large eddy simulation (LES). Two sets of simulations were taken into account for 10% and 20% exhaust gas recirculation (EGR) fractions. In the first one, the main injection was split into two identical phases, while in the second one into three pulses. Within each set, three strategies were considered, increasing the amount of fuel injected during the main and concurrently decreasing the post pulse. Overall, 48 simulations were employed, since four different dwells between the last phase of the main and post injection were considered. Results show that the pollutant emissions minimization has been obtained for the Schemes injecting 65% and 70% of fuel for both two and three split strategies, but for different values of dwell. In fact, emissions very close to each other for NOx and particulate matter have been reached for these cases. Reductions of about -30% and -71% were respectively obtained for NOx and soot in comparison with experimental emissions related to the single injection case. [ABSTRACT FROM AUTHOR]

Precast reinforced concrete technology has been widely applied in Italy for industrial facilities throughout the years and nowadays older buildings show structure and energy-related deficiencies. In order to promote integrated redevelopment interventions, the research sets a methodological framework to investigate such a vast building stock and proposes a classification of the different typological variants registered according to structural, architectural, and technological aspects. This paper focuses on the industrial building stock realized recurring to prefabrication techniques in the geographical cluster of Casentino, in Tuscany. The research involved 675 buildings intended for production activities whose specifications were collected in a GIS database as alphanumerical parameters. Data, obtained through digital surveys, aerial views, and on-field recognitions, were postprocessed to provide a general overview of the most recurring characteristics and highlight evolutionary trends over years. Seven typological declinations were identified for prefabricated reinforced concrete industrial buildings and their diffusion was related to the different periods of constructions. Roofing systems, structural solutions, and external wall components were chosen as key parameters for the classification procedures. The definition of recurrent typological solutions in industrial buildings is meant as a preparatory operation that will facilitate the assessment of their current architectural, technological, structural, and specifically energy and environmental performances. This research paves the way toward the development of protocols and guidelines containing integrated retrofitting strategies and solutions tailored on the specific issues of each variant. [ABSTRACT FROM AUTHOR]

In general, the aerosols mixed in air medium can be regularly manipulated by means of the interactions between the aerosols and the acoustic field. The manipulable properties of aerosols can be engineered through geometric parameter and acoustic resonance condition of the underlying device. The aerosols manipulated by modulated multiple acoustic wavepackets (MAWP) in acoustic resonance condition is proposed and demonstrated in this paper, whose application belongs to an efficient aerosol removal technique. The experimental results indicated that the removal efficiency of aerosols was mainly influenced by the different harmonic order. The technique and process proposed in this paper was feasible for industrial application. The MAWP is modulated by means of the synthetic standing wave field at the resonant frequency 1.268 kHz. The aerosol manipulation processes through MAWP consist of the aerosol shift, collision aggregation and deposition between the dot and the anti-neck of a single wavepacket. As a visual inspection confirming standing wave, the processes may also be applied in modulating the MAWP simultaneously. The manipulation efficiency can be increased due to the increase of wavepacket amount under the same operating conditions. The acoustic radiation force causes shift and accumulation of aerosol in waveguide and the secondary radiation force enhances collision aggregation and deposition thereof. The initial number concentration of particles < 2.5 μm (resp. larger than 2.5 μm) was about 517,488 1/cf 3 (resp. 51,918 1/cf 3 ). Under the action of these forces, the aerosols in waveguide were aggregated and deposited onto the inner wall of waveguide. At the end of experiment, the final number concentration of particles < 2.5 μm (resp. larger than 2.5 μm) is about 59,096 1/cf 3 (resp. 392 1/cf 3 ). The PM 2.5 content of aerosols used in experiment is about 91%. The removal coefficients are larger than 85%. The deposition stripe distribution shows the specific pattern associated with a wavepacket. The surface of the stripe particles is covered with the uniform small hollows (~ 105.7–177.7 nm), and plenty of nanoscale particles (~ 13.66–16.55 nm) are grown around the surface of small hollows. It may be possible to develop a new way for large scale and batch aerosol processing to apply to the prospective emission control of industrial aerosols. [ABSTRACT FROM AUTHOR]

Abstract: The development of reliable fuel cells power plant based on renewable fuels stands out as one of the promising energy systems solutions for the future. Indeed fuel cells can increase the efficiency and the cleaning of the electrical energy production from renewable fuels. Process simulations of advanced power plants fed by low cost renewable fuels like biomass waste are a key step to develop renewable resources based on high temperature fuel cells applications. The aim of this work is to predict the component behaviour of a specific power plant mainly composed of a small indirectly heated gasifier and a Solid Oxide Fuel Cell (SOFC) and fed by chestnut coppice, waste available in great quantity in Central Italy, as well as in several other European regions. The plant''s thermodynamic behaviour is analysed by means of the process simulator CHEMCAD© in which particular models for the SOFC and the gasifier have been developed in FORTRAN by the authors and then interfaced to commercial software. The results of the predictive model are presented and discussed, showing the possibility of an extremely interesting “carbon neutral” small plant configuration with high electrical and global efficiency exclusively based on the use of low cost renewable resources. [Copyright &y& Elsevier]

Abstract: In order to obtain an acceptable rate of survival of the frozen cells, they must be first cooled in programmable freezers, while controlling the cooling rate, and then stored in maintenance freezers. Different solutions are already used to preserve cells at cryogenic temperatures without liquid nitrogen, while this is not true for controlling the cooling rate. A Pulse Tube (PT) cryorefrigeration system type, can be used in the automatic freezing if combined with a system that monitors and “drives” the temperature generated on the cold part (cold head). To make the Pulse Tube system a suitable one for freezing processes, the cooling curve must be “corrected” in a linear one with a slope given by requested cooling rate. The temperature regulation is obtained with the use of a power dissipator based on Joule effect. In this study, the power to be dissipated is calculated individualizing the trend of temperature on the Pulse Tube cold head and inside the cell test tubes. The control system is not based on an historical series of data so it can be used in different operative conditions. The obtained temperature curve is in good agreement with the theoretical values, with errors within those accepted by commercial systems. The Pulse Tube cryorefrigerator may represent a valid alternative solution to programmable liquid nitrogen freezer, especially where nitrogen’s supply is difficult or extremely expensive. [ABSTRACT FROM AUTHOR]

An experimental investigation on air natural convection, in a vertical channel asymmetrically heated at uniform heat flux, with downstream unheated parallel extensions, is carried out. One extension is coplanar to the unheated channel wall and the distance between the extensions is equal to or greater than the channel gap (geometrically asymmetric chimney). Experiments are performed with different values of the wall heat flux, aspect ratio (Lh/b), extension ratio (L/Lh) and expansion ratio (B/b). For the largest value of the aspect ratio (Lh/b= 10), the adiabatic extensions improve the thermal performance in terms of lower maximum wall temperature of the channel Optimal configurations of the system with asymmetrical chimney are detected. Flow visualization shows a cold inflow in the channel-chimney system that penetrates down below the channel exit section. Maximum wall temperatures and channel Nusselt numbers are correlated to the channel Rayleigh number, Ra*, and to the geometrical parameters, in the ranges 3.0 x 10² ≤ Ra*B/b ≤ 1.0105, 1.0 ≤ B/b 3.0 and 1.0 ≤ L/Lh ≤ 4.0 with Lh/b = 5.0 and 10.0. [ABSTRACT FROM AUTHOR]

Air natural convection in an asymmetrically heated channel with unheated extensions has been investigated experimentally. Local and maximum wall temperatures and heat transfer coefficients are presented, for different values of the process parameters. Optimal configurations in terms of the minimum values of maximum wall temperatures are obtained. Average Nusselt numbers and maximum dimensionless wall temperatures are correlated to the Rayleigh number and to the geometrical dimensionless parameters in the 10–1.5×105 range of the Rayleigh number times the expansion ratio. The addition of downstream unheated extensions improves the thermal performance of the channel for some configurations, the longer the extension and the lower the aspect ratio the lower the wall temperature in the channel. [Copyright &y& Elsevier]

Presents a study that examined air natural convection on an inclined discretely heated plate with a parallel shroud below. Information on natural convection; Details of the flow visualized patterns of the air; Evaluation and correlation of Nusselt numbers to the significant process parameters; Results of the study.

In Italy in 2020, only 15.5% of school building heritage was retrofitted from an energy and environmental point of view. In this paper, the cost-optimal method was applied to two different school buildings belonging to the same Italian cold climate zone but characterized by different structural and technological solutions. The research aims at defining the cost-effective redevelopment solution among several ones proposed to apply to this building type. At the same time, this paper provides a critical analysis of the methodology applied, highlighting deficiencies related to a not proper evaluation of environmentally friendly retrofitting measures. In a cost-effective context, the main results show that the intervention on the heating system is more convenient than the retrofitting of the envelope. The energy saving is equal to about 35% for both considered schools. Among the different proposed requalification configurations, the adoption of PV (photovoltaic) electric generation is included. In this regard, an optimization procedure was implemented in a generative design environment to maximize energy production with reference to different design parameters. As a result, a solution with south oriented PV modules with a tilt angle of 42° and arranged in 0.7 m spaced rows proved to be the most effective. [ABSTRACT FROM AUTHOR]

A smart possible way to cool electronics equipment is represented by passive methods, which do not require an additional power input, such as Phase Change Materials (PCMs). PCMs have the benefit of their latent heat being exploited during the phase change from solid to liquid state. This paper experimentally investigates the melting of different PCMs having different melting temperatures (42, 55 and 64 °C). Two copper foams, having 10 PPI and relative densities of 6.7% and 9.5%, i.e., porosities of 93.3% and 90.5%, respectively, are used to enhance the thermal conductivity of PCMs. The block composed by the PCM and the copper foam is heated from one side, applying three different heat fluxes (10, 15 and 20 kW m−2): the higher the heat flux, the higher the temperature reached by the heated side and the shorter the time for a complete melting of the PCM. The copper foam with a relative density of 9.5% shows slightly better performance, whereas the choice of the melting temperature of the PCM depends on the time during which the passive cooling system must work. The effect of the foam material is also presented: a copper foam presents better thermal performances than an aluminum foam with the same morphological characteristics. Finally, experimental dimensionless results are compared against values predicted by a correlation previously developed. [ABSTRACT FROM AUTHOR]

The high efficiency of concentrated solar power (CSP) in energy conversion makes it a very attractive device for using solar energy as a substitute of nonrenewable energy sources. The open volumetric receiver plays an important role in the performance of a CSP. The optimized design of solar receiver implies the thorough knowledge of the heat transfer between the air and the foam and of the temperature distribution in the receiver. Heat transfer in the cylindrical SiC porous volumetric receiver of a solar tower, undergoing the impact of concentrated solar radiation, is investigated numerically in this paper. Governing equations are written with the volume averaging technique. A two-equation model for the energy equation, under the local thermal nonequilibrium assumption, is used. Numerical simulations are carried out through the commercial code COMSOL Multiphysics. The solid and fluid temperatures, the fluid velocity and the pressure drop, for various boundary and morphological conditions, are predicted and discussed. The receiver efficiency is finally maximized carrying out an extended parametric analysis of process parameters. [ABSTRACT FROM AUTHOR]

Diesel exhaust aerosols (DEAs) can absorb and accumulate toxic metal particulates and bacteria suspended in the atmospheric environment, which impact human health and the environment. The use of acoustic standing waves (ASWs) to aggregate DEA is currently considered to be an efficient particle removal method; however, study of the effect of different temperatures on the acoustic aggregation process is scarce. To explore the method and technology to regulate and optimize the aerosol aggregation process through temperature tuning, an acoustic apparatus integrated with a temperature regulation function was constructed. Using this apparatus, the effect of different characteristic temperatures (CTs) on the aerosol aggregation process was investigated experimentally in the ASW environment. Under constant conditions of acoustic frequency 1.286 kHz, voltage amplitude 17 V and input electric power 16.7 W, the study concentrated on temperature effects on the aggregation process in the CT range of 58–72°C. The DEA opacity was used. The results demonstrate that the aggregation process is quite sensitive to the CT, and that the optimal DEA aggregation can be achieved at 66°C. The aggregated particles of 68.17 μm are composed of small nanoparticles of 13.34–62.15 nm. At CTs higher and lower than 66°C, the apparatus in non-resonance mode reduces the DEA aggregation level. For other instruments, the method for obtaining the optimum temperature for acoustic agglomeration is universal. This preliminary demonstration shows that the use of acoustic technology to regulate the aerosol aggregation process through tuning the operating temperature is feasible and convenient. [ABSTRACT FROM AUTHOR]

The knowledge of thermal transport characteristics is of primary importance in the application of foams. The thermal characteristics of a foam heavily depend on its microstructure and, therefore, have to be investigated at a pore level. However, this analysis is a challenging task, because of the complex geometry of a foam. The use of foam models is a promising tool in their study. The Kelvin and the Weaire-Phelan foam models, among the most representative practical foam models, are used in this paper to numerically investigate heat transfer and pressure drop in metallic foams. They are developed in the "surface evolver" open source software. Mass, momentum, and energy equations, for air forced convection in open cell foams, are solved with a finite-element method, for different values of cell size and porosity. Heat transfer and pressure drop results are reported in terms of volumetric Nusselt number and Darcy-Weisbach friction factor, respectively. Finally, a comparison between the numerical predictions obtained with the two foam models is carried out, in order to evaluate the feasibility to substitute the more complex and computationally heavier Weaire-Phelan foam structure with the simpler Kelvin foam representation. Negligible differences between the two models are exhibited at high porosities. [ABSTRACT FROM AUTHOR]

It is our great pleasure and honor to present this special issue ofHeat Transfer Engineeringto highlight some of the research works presented at the ASME-ATI-UIT 2015 Conference on Thermal Energy Systems: Production, Storage, Utilization, and the Environment that took place on May 17–20, 2015, in Napoli, Italy. The conference was organized under the auspices of the American Society of Mechanical Engineers (ASME), Associazione Termotecnica Italiana (ATI), and Unione Italiana di Termofluidodinamica (UIT). [ABSTRACT FROM PUBLISHER]

Metal foams are being widely adopted in a number of applications relevant to heat transfer, in which many include thermal radiation as the predominant heat transfer mode. Radiative characteristics of porous media are determined either by analytical modeling or by experiments. The aim of the present study is to evaluate the feasibility to substitute the real structure, more complex and computationally expensive, with the simpler and lighter ideal foam representation. The radiative heat transfer in foams is investigated using home-made Monte Carlo Ray Tracing codes. The geometry of the real microstructure of a metal foam is obtained by employing X-ray computed tomography (XCT). The actual 3-D structure is imaged, from which the total porosity, surface to volume ratio and size of a representative elementary volume for thermal analysis are determined. Results from the tomographic structures are compared to computer-generated Kelvin and Weaire–Phelan foam structures. Numerical results obtained for the real and ideal geometries are compared. The agreement is good, especially when accounting for the effect of the ligament shape. The good agreement between the results obtained with reference to the Weaire–Phelan convex ligament structures and those for real structures, both in terms of extinction coefficients and scattering phase functions, suggests that such idealized structures can estimate with good accuracy the parameters for equivalent homogeneous media on the basis of the porosity and the specific surface area. [ABSTRACT FROM AUTHOR]

Because of their light weight, open porosity, high surface area per unit volume, and ther-mal characteristics, metal foams are a promising material for many industrial applica-tions involving fluid flow and heat transfer. The pressure drop and heat transfer in porous media have inspired a number of experimental and numerical studies, and many models have been proposed in the literature that correlate the pressure gradient and the heat transfer coefficient with the mean cell size and porosity. However, large differences exist among results predicted by different models, and most studies are based on idealized per-iodic cell structures. In this study, the true three-dimensional microstructure of the metal foam is obtained by employing x-ray computed microtomography (XCT). This is the "real" structure. For comparison, ideal Kelvin foam structures are developed in thefree-to-use software "surface evolver" surface energy minimization program. These are "ideal" structures. Pressure drop and heat transfer are then investigated in each struc-ture using the CFD module of COMSOL' Multiphysics code. A comparison between the numerical predictions from the real and ideal geometries is carried out. The predictions showed that heat transfer characteristics are very close for low values of Reynolds num-ber, but larger Reynolds numbers create larger differences between the results of the idea! and real structures. Conversely, the differences in pressure drop at any Reynolds number are nearly 100%. Results from the models are then validated by comparing them with experimental results taken from the literature. The validation suggests that the ideal structure poorly predicts the heat transfer and pressure drops. [ABSTRACT FROM AUTHOR]

Abstract: A theoretical approach proposed in the literature has been used to develop a new radiative heat transfer model based on the tetrakaidecahedric representation of open cell metal foams proposed by Lord Kelvin. The analytical approach has been combined with numerical simulations based onto ray-tracing Monte Carlo method. An iterative matrix algebra implemented procedure has been used to consistently calculate the coefficients involved in view factors. The radiative conductivity of foams has been evaluated by means of the proposed model. Predictions are compared both with experimental results from the literature, obtained on several metallic foams, and with predictions given by an existing simpler model based on a cubic representation of the foam unit cell. The agreement of experimental results with predictions derived by means of the proposed model is good and far better than that with predictions by the simpler model. [Copyright &y& Elsevier]

Abstract: A simplified analytical–numerical method to model radiation heat transfer in metallic foams is proposed. It modifies a model taken from the literature and allows to predict the radiative conductivity for high and low porosity foams. A simplified cubic representative elementary volume of the foam is assumed and radiative heat flux is evaluated by computing radiosities and view factors. The analytical approach proposed in this paper slightly modifies some coefficients of the original model. Test ray-tracing and numerical simulations based onto Monte Carlo method are carried out in order to consistently calculate some view factors. The comparison with experimental results shows that predictions of the proposed model are more accurate than those of the original one. [Copyright &y& Elsevier]

A numerical investigation of mixed convection in air due to the interaction between a buoyancy flow and the flow induced by a moving plate in a vertical channel is carried out. An unheated plate moves at a constant velocity in the direction of the buoyancy force and the principal walls of the channel are heated at uniform heat flux. The effects of the channel spacing, heat flux and moving plate velocity are investigated and results in terms of the channel walls and moving plate temperatures, air velocity profiles inside the channel, wall stress along the channel wall and the moving plate and Nusselt numbers are given. A composite correlation between Nusselt number and Reynolds and Richardson numbers is proposed in the range from natural convection to forced convection up to Re = 1.32 × 104 and 9.86 × 10−6 ≤ Ri ≤ 1.15 × 103, for the channel aspect ratio in the [20.3–81.2] range. [ABSTRACT FROM AUTHOR]

The aim of this work was the evaluation of the catalytic steam reforming of a gaseous fuel obtained by steam biomass gasification to convert topping atmosphere residue (TAR) and CH4 and to produce pure H2 by means of a CO2 sorbent. This experimental work deals with the demonstration of the practical feasibility of such concepts, using a real woodgas obtained from fluidized bed steam gasification of hazelnut shells. This study evaluates the use of a commercial Ni catalyst and calcined dolomite (CaO/MgO). The bed material simultaneously acts as reforming catalyst and CO2 sorbent. The experimental investigations have been carried out in a fixed bed micro-reactor rig using a slipstream from the gasifier to evaluate gas cleaning and upgrading options. The reforming/sorption tests were carried out at 650 °C while regeneration of the sorbent was carried out at 850 °C in a nitrogen environment. Both combinations of catalyst and sorbent are very effective in TAR and CH4 removal, with conversions near 100%, while the simultaneous CO2 sorption effectively enhances the water gas shift reaction producing a gas with a hydrogen volume fraction of over 90%. Multicycle tests of reforming/CO2 capture and regeneration were performed to verify the stability of the catalysts and sorbents to remove TAR and capture CO2 during the duty cycle. [ABSTRACT FROM AUTHOR]

Abstract: A numerical investigation of mixed convection in air due to the interaction between a buoyancy flow and the flow induced by a moving plate in a vertical channel is carried out. An adiabatic plate moves at a constant velocity in the mid-plane of the channel in the direction of the buoyancy force and the principal walls of the channel are heated at uniform heat flux. The effects of the channel aspect ratio, Rayleigh and Reynolds numbers are investigated and results in terms of the dimensionless channel wall and moving plate temperatures are given. Results show that the larger the channel aspect ratio, , the stronger the effects of the moving plate. Increasing Reynolds number significantly decreases the dimensionless temperature of the channel walls. A composite correlation between Nusselt number and Reynolds and Richardson numbers is proposed in the range from natural convection to forced convection up to and , for the channel aspect ratio in the [20.3–81.2] range. [Copyright &y& Elsevier]

Natural convection in a convergent channel with finite-thickness principal walls at uniform heat flux is investigated numerically. Heat conduction in the walls and the effects of walls emissivity are taken into account. Laminar two-dimensional steady-state conditions are assumed. Results in terms of wall dimensionless temperature profiles as a function of convergence angle, channel spacing, and heat flux are given for various values of wall emissivity. Wall temperatures decrease significantly, passing from δ = 0° to 2° at the lowest channel spacing. Streamlines and temperature fields show a recirculating region in the channel for large values of L w / b min and for δ equal to 5° and 10°. Correlations between Nusselt numbers and Rayleigh numbers are proposed. Dimensionless parameters are in the following ranges: 4.4 ≤ Ra′ bmin ≤ 1.5 × 10 5 , 10 ≤ L w / b min ≤ 58, 0.0 ≤ ε ≤ 1.0, and 0° ≤ δ ≤ 10°. Numerical predictions are in very good agreement with experimental data. [ABSTRACT FROM AUTHOR]

Graded foam-filled channels are a very promising solution for improving the thermal performance of heat sinks because of their customized structures that leave large amounts of room for heat transfer enhancement. Accordingly, this paper proposes a comprehensive optimization framework to address the design of such components, which are subjected to a uniform heat flux boundary condition. The graded foam is achieved by parameterizing the spatial distributions of porosity and/or Pores Per Inch (PPI). Mono- and multi-objective optimizations are implemented to find the best combination of the foam's fluid-dynamic, geometrical and morphological design variables. The mono-objective approach addresses the Performance Evaluation Criterion (PEC) as an objective function to maximize the thermal efficiency of graded foams. The multi-objective approach addresses different objective functions by means of Pareto optimization to identify the optimal tradeoff solutions between heat transfer enhancement and pressure drop reduction. Optimizations are performed by assuming a local thermal non-equilibrium in the foam. They allowed us to achieve a 1.51 PEC value with H* = 0.50, ReH = 15000, iε = iPPI = 0.50, ε(0) = 0.85, ε(1) = 0.97, PPI(0) = 5, PPI(1) = 40, and ks→f = 104 as the design variables. For the three multi-objective functions investigated, one can extrapolate the optimum from the Pareto front via the utopia criterion, obtaining h ¯ = 502 W/m2 K and Δp = 80 Pa, Nu H , unif ¯ = 2790 and f = 42, 〈 T s * 〉 s ¯ = 0.011, and Δp* = 91. The optimal solutions provide original insights and guidelines for the thermal design of graded foam-filled channels. [ABSTRACT FROM AUTHOR]

The thermal performance of several engineering devices, such as heat exchangers, volumetric solar receivers and thermal energy storage systems, is improved by open-cell metal or ceramic foams. Among them functionally-graded foams, through which morphological characteristics are variable, look promising. Heat transfer and pressure drop in a functionally-graded foam, with a uniform heat flux entering one of its sides, are investigated numerically in this paper. Porosity and cell size variable in the direction of the entering heat flux according to different power-law functions are considered; their maximum and minimum values are constrained at the opposite upper and lower sides of the foam. Governing equations, written with reference to a Representative Elementary Volume (REV) of the foam, are solved with a Local Thermal Non Equilibrium (LTNE) model by means of a finite element scheme; the code is validated with experimental data from the literature. The thermal performance of the foam is expressed by a Performance Evaluation Criterion (PEC), referred to the average morphological characteristics of foams with the same surface area. Nusselt numbers, friction factors and Performance Evaluation Criteria (PECs), for different power-laws, are predicted. A 38% higher PEC than in foams with uniform porosity is found in foams with variable-porosity while a 14% larger PEC is exhibited in foams with variable cell size. A 42% increase in PEC is found in foams that account for both variable porosity and cell size. • Heat transfer and pressure drop in a functionally-graded foam are analyzed numerically. • Different power-law functions for porosity and cell size are considered. • Nusselt numbers, friction factors and PECs are predicted. • PEC is 38% and 14% higher than in foams with uniform porosity or PPI, respectively. • A 42% increase in PEC is exhibited by foams with both variable porosity and PPI. [ABSTRACT FROM AUTHOR]

• Anisotropy convective heat transfer in metal foams is numerically analyzed. • Foams geometry is reconstructed with x-ray Computed Tomography (xCT). • Directional heat transfer coefficients for different porosities are predicted. • The relationship between heat transfer and the cell elongation is highlighted. • A correlation between Nusselt and Reynolds number as well as porosity is presented. Open-cell metal foams are promising materials for heat transfer augmentation, due to their tortuosity and high specific surface area. The volume-averaging technique under the assumption of local thermal non-equilibrium between the solid and fluid phases is often used to model devices equipped with open-cell foams; it requires an accurate knowledge of the interfacial convective heat transfer coefficient. Its dependence on the anisotropy of elongated foam cells is investigated numerically in the present work. Four aluminum foam samples with different porosities and equal PPIs are considered; their geometry is reconstructed by means of x-ray computed tomography. Mass, momentum and energy equations for the fluid phase (air) are solved, while the solid phase is accounted for with a uniform heat flux boundary condition. Interfacial convective heat transfer coefficients and Nusselt numbers are predicted. The dependence of the interfacial heat transfer coefficient in the elongation direction on the effective porosity and fluid inlet velocity is pointed out. The comparison of predicted values with those given by correlations from the open literature shows a good agreement. Finally, correlations for the prediction of Nusselt numbers, accounting for the foam anisotropy, are proposed, which can be useful in the study of metal foams. [ABSTRACT FROM AUTHOR]