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Nowadays, the need for developing more effective heat exchange technologies and innovative materials, capable of increasing performances while keeping power consumption, size and cost at reasonable levels, is well recognized. Under this perspective, metal foams have a great potential for enhancing the thermal efficiency of heat transfer devices, while allowing the use of smaller and lighter equipments. However, for practical applications, it is necessary to compromise between the augmented heat transfer rate and the increased pressure drop induced by the tortuous flow passages. For design purposes, the estimation of the flow permeability and the thermal conductivity of the foam is fundamental, but far from simple. From this perspective, besides classical transport models and correlations, computational fluid dynamics (CFD) at the pore scale, although challenging, are becoming a promising approach, especially if coupled with a realistic description of the foam structure. For precisely recovering the microstructure of the foams, a 3D X-ray computed microtomography (-CT) can be adopted. In this work, the results of -CT-based CFD simulations performed on different open-cell aluminum foams samples will be discussed. The results demonstrate that open-cell aluminum foams are effective means for enhancing heat transfer.

Streamwise-periodic variation of cross-sectional area causes the flow and the non-dimensional temperature fields to repeat periodically, after a certain developing length, in a variety of systems of practical interest. For these geometries, the numerical simulation of heat transfer and fluid flow can be conveniently confined to a single isolated module, thus to neglect the effect of the dynamic and thermal development and with a significant saving in computational resources. In this paper, a thorough review of the relevant literature is presented. While the solution of the periodic flow field is performed in a similar way in nearly all the studies that have been examined, different solution strategies for the temperature field have been published, for both cases of imposed wall heat flux and assigned wall temperature. The solution of the fully developed temperature field is more challenging than the solution of the periodic flow field, and for this reason both analytically accurate and approximate methods have been found in the relevant scientific literature. Solution techniques for both thermal boundary conditions have been implemented and successfully tested in ANSYS CFX. Although the implementation of a complete, non-iterative analytical model for a prescribed wall temperature boundary condition proved to be almost impossible, because of the difficulties associated to the lack of access to the detailed data structure within the code, an original improvement of a simpler and only slightly less accurate method found in the literature has been developed, and will be presented.

Metal foams have a great potential for enhancing the thermal performances of heat transfer devices, while allowing the use of smaller and lighter equipments. From a practical standpoint, it is necessary to compromise between the improved heat transfer rate and the higher pressure drop induced by the tortuous flow passages. In order to investigate the structure and properties of metal foams, and to provide adequate information for design purposes, the prediction of the permeability and thermal conductivity as a function of the structural characteristics would be desirable. From this perspective, computational fluid dynamics (CFD) computations at the pore scale are becoming a challenging approach in addition to classical transport models. To investigate the microstructure of metal foams, a three-dimensional approach by using X-ray computed microtomography (μ-CT) can be adopted. μ-CT is a nondestructive characterization technique representing a powerful investigation tool in many different applications. It consists in recording a number of projections of the sample at different angles, and reconstructing a 3D image with the help of a suitable algorithm. The reconstructed 3D dataset can be employed, after adequate geometric manipulation, to perform a CFD simulation on a realistic medium. In this work, a review of the recent experimental and numerical advances in the characterization of metal foams transport properties will be illustrated. Moreover, we will present the results of a high resolution 3D μ-CT imaging of three Aluminum foam samples, with different pore per inch values, performed at the TomoLab station, located at the Elettra Synchrotron Radiation Facility in Trieste.

In the continuous casting process of steel, the control of the mould heat removal is a key parameter, since it directly affects the shell growth and the stresses and strains that are produced in the mould. An inverse heat conduction model was developed to calculate mould heat transfer from temperature measurements, recorded using thermocouples buried inside the copper mould wall. The mould is water-cooled to solidify the hot metal directly in contact with it. The direct stationary conduction problem was solved both on a 2D and a 3D domain; the 2D geometry concerns only a longitudinal section of the mould, while in the 3D domain a whole face is considered. The inverse problem was solved using a Conjugate Gradient algorithm, a Genetic Algorithm and the Nelder - Mear SIMPLEX algorithm. For the 3D geometry, the heat flux profile calculated at the axis of the face is close to that obtained from the 2D model, although the former is slightly lower. For both geometries, there is a good agreement between numerical and experimental temperatures. Moreover, the 3D model provides a better estimate of the outlet water temperature.

Inverse Heat Transfer Problems rely on temperature measurements for the estimation of unknown quantities (e.g. boundary or initial conditions, thermophysical properties); this kind of problems is classified as ill-posed. An application of the inverse analysis in the continuous casting process of steel is here presented. The aim is the estimation of the mould heat transfer starting from temperature measurements, recorded using thermocouples buried inside the copper mould wall. The mould is water-cooled to solidify the hot metal directly in contact with it. The direct stationary conduction problem was solved both on a 2D and a 3D domain. The inverse problem was solved using Gradient algorithms, Genetic Algorithms and SIMPLEX. For both geometries, a good agreement between numerical and experimental temperature values is observed; moreover, the 3D model provides a better estimate of the outlet temperature of the cooling water.

Il tubo di Ranque – Hilsch è un dispositivo, privo di parti in movimento, capace di separare una corrente d'aria ad alta pressione in due correnti distinte, una a temperatura superiore ed una a temperatura inferiore a quella del fluido in ingresso. Il moto del fluido all’interno del dispositivo e la separazione dell’energia che si realizza sono stati simulati numericamente utilizzando il software ANSYS CFX 11.0 e prendendo come riferimento lo studio numerico/sperimentale condotto da Skye et al. [1]. La separazione dell’energia all’uscita fredda, ottenuta utilizzando il modello di turbolenza k-ε, si avvicina ai dati sperimentali di Skye et al. in misura nettamente maggiore dei risultati di simulazioni CFD del medesimo autore.

Nowadays, the need for developing more effective heat transfer technologies and innovative materials, capable of increasing performances while keeping power consumption, cost and size at reasonable levels, is well understood. Under this perspective, metal foams are gaining attention in view of their potential for increasing the thermal efficiency of heat transfer devices, while allowing the use of smaller and lighter equipments. In this work, the results of high-resolution X-ray microtomography-based CFD simulations, performed on three open-cell aluminum foams samples of different pore densities (10–20–30 PPI), will be illustrated. The computed values of permeability and effective thermal conductivity are reported and compared to the corresponding experimental values available in the literature. The flow simulations were conducted with an incompressible flow of air at steady state and in laminar flow regime (the Reynolds number, defined on the nominal pore diameter of the foam and the superficial velocity, was varied between 1 and 100).

Optimization of heat exchangers, as a consequence of their vital role in several industries and applications, has attracted a lot of interest in the last years, and in particular the necessity of improving their performances is well recognized. The coupling of optimization techniques with Computational Fluid Dynamics (CFD) has demonstrated to be a valid methodology for easily explore this work, a CFD-based shape optimization of a tube bundle in crossflow is presented, as a natural extension of the work of Hilbert et al. (2006) [1]. In this study, also the flow inside the tubes has been computed, and the coupled simulation of the external flow and thermal field is performed also on a periodic domain. Two genetic algorithms have been tested and compared, NSGA-II and FMOGA-II: the latter makes an internal use of surrogate models to speed up and improve the optimization process, and proved to be a promising algorithm. The results demonstrate how the search for efficient geometric configurations should also take into account the internal flow field.

The necessity for devising more effective heat transfer technologies and innovative materials, capable of increasing performances while keeping power consumption, size and cost at reasonable levels, is well recognized. Under this prospect, metal foams are good candidates for improving the thermal efficiency of heat transfer devices and allowing, at the same time, the use of smaller and lighter equipments. For design purposes, the proper characterization and quantification of transport and thermal properties of metal foams is fundamental but far from simple. This lack of information constitutes a fundamental limit in the employment of metal foams in practical and industrial applications. Nowadays, besides classical transport models and correlations, computational fluid dynamics (CFD) at the pore scale, although challenging, are becoming a promising approach for recovering the transport properties of the medium, especially if coupled with a realistic description of the foam structure. In order to precisely describe the microstructure of the foams, a 3D approach based on the X-ray computed microtomography (μ-CT) technique can be adopted. In this work, the results of high resolution μ-CT-based CFD simulations, performed on three different open-cell aluminum foams samples, will be illustrated. The results demonstrate that open-cell aluminum foams are effective means for enhancing heat transfer. Moreover, the procedure proved that μ-CT is a valid tool for capturing the peculiar details of the foam structure, thus to overcome the limits associated to the use of economical, but simplified, geometric models.

The main purpose of this study is the development of an innovative methodology for Heat Exchangers (HE) design to replace the conventional design procedures. The new procedure is based on the definition of a software package managed by modeFRONTIER, a multi-objective optimization software produced by ESTECO, able to create HE virtual models by targeting several objectives, like HE performance, optimal use of material, HE minimal weight and size and optimal manufacturability. The proposed methodology consists first in the definition of a workflow for the automatic CFD simulation of a parametric model of a periodic HE cellular element. This is followed by the definition of a Response Surface (meta-model) covering all the possible range of parameters' combination, the definition of a “bridge”, e.g. low-fidelity - standard or macroscopic - models to extend the behavior of the liquid and air HE cellular elements to a real scale HE, and an optimization process to obtain the optimal HE design for any proposed application and requirements. The versatility of the methodology, thanks to the modularity of modeFRONTIER platform, offers the possibility of a large scenario of applications for Fluid Power systems, where Heat Exchangers (for both fixed and mobile applications) are used to cool down the oil or any other working fluid. In this work the main aspects covering the background of the project, the proposed methodology and the expected benefits will be introduced. In addition, validation of the CFD models with experimental data available in the literature will be illustrated, as well as an example of “bridge” optimization with the use of experimental correlations available in the literature.

Knowing the effective thermal conductivity is essential in order to design a metal foam heat transfer device. Beside the experimental characterization tests, this quantity can be deduced from empirical correlations and theoretical models. Moreover, CFD (Computational Fluid Dynamics) and numerical modeling in general, at the pore scale, are becoming a promising alternative, especially when coupled with a realistic description of the foam structure, which can be recovered from X-ray computed microtomography (μ-CT). In this work, a review of the most relevant correlations and models published in the literature, usable for the estimation of the effective thermal conductivity of metal foams, will be outlined. In addition, a validation of the models with the experimental values available in the literature will be presented, for both air and water as working fluids. Furthermore, the results of a strategy based on μ-CT – CFD coupling at the pore level will be illustrated.

In the continuous casting process of steel, the control of the mould heat removal is a key parameter, since it directly affects the shell growth and the stresses and strains that are produced in the mould. An inverse heat conduction model was developed to calculate mould heat transfer from temperature measurements, recorded using thermocouples buried inside the copper mould wall. The mould is water-cooled to solidify the hot metal directly in contact with it. The direct stationary conduction problem was solved both on a 2D and a 3D domain; the 2D geometry concerns only a longitudinal section of the mould, while in the 3D domain a whole face is considered. The inverse problem was solved using a Conjugate Gradient algorithm, a Genetic Algorithm and the Nelder-Mear SIMPLEX algorithm. For the 3D geometry, the heat flux profile calculated at the axis of the face is close to that obtained from the 2D model, although the former is slightly lower. For both geometries, there is a good agreement between numerical and experimental temperatures. Moreover, the 3D model provides a better estimate of the outlet water temperature.Copyright © 2011 by ASME

Nowadays, the need for developing more effective heat exchange technologies and innovative materials, capable of increasing performances while keeping power consumption, size and cost at reasonable levels, is well recognized. Under this perspective, metal foams have a great potential for enhancing the thermal efficiency of heat transfer devices, while allowing for the use of smaller and lighter equipments. However, for practical applications, it is necessary to compromise between the augmented heat transfer rate and the increased pressure drop induced by the tortuous flow passages. For design purposes, the estimation of the flow permeability and the thermal conductivity of the foam is fundamental, but far from simple. From this perspective, besides classical transport models and correlations, computational fluid dynamics (CFD) at the pore scale, although challenging, is becoming a promising approach, especially if coupled with a realistic description of the foam structure. For precisely recovering the microstructure of the foams, a 3D X-ray computed microtomography (μ-CT) can be adopted. In this work, the results of μ-CT-based CFD simulations performed on different open-cell aluminum foams samples, for laminar flow regime, will be discussed. The results demonstrate that open-cell aluminum foams are effective means for enhancing heat transfer.