Pore-scale numerical investigation of pressure drop behaviour across open-cell metal foams

The development and validation of a grid-based pore-scale numerical modelling methodology applied to five different commercial metal foam samples is described. The 3-D digital representation of the foam geometry was obtained by the use of X-ray microcomputer tomography scans, and macroscopic properties such as porosity, specific surface and pore size distribution are directly calculated from tomographic data. Pressure drop measurements were performed on all the samples under a wide range of flow velocities, with focus on the turbulent flow regime. Airflow pore-scale simulations were carried out solving the continuity and Navier–Stokes equations using a commercial finite volume code. The feasibility of using Reynolds-averaged Navier–Stokes models to account for the turbulence within the pore space was evaluated. Macroscopic transport quantities are calculated from the pore-scale simulations by averaging. Permeability and Forchheimer coefficient values are obtained from the pressure gradient data for both experiments and simulations and used for validation. Results have shown that viscous losses are practically negligible under the conditions investigated and pressure losses are dominated by inertial effects. Simulations performed on samples with varying thickness in the flow direction showed the pressure gradient to be affected by the sample thickness. However, as the thickness increased, the pressure gradient tended towards an asymptotic value

Simulazione numerica dell\u2019effetto di separazione dell\u2019energia per tubi di Ranque-Hilsch

Il tubo di Ranque \u2013 Hilsch \ue8 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\u2019interno del dispositivo e la separazione dell\u2019energia 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\u2019energia all\u2019uscita fredda, ottenuta utilizzando il modello di turbolenza k-\u3b5, si avvicina ai dati sperimentali di Skye et al. in misura nettamente maggiore dei risultati di simulazioni CFD del medesimo autore

Metal Foams for Enhanced Heat Transfer. State of the Art and XRayMicrotomography Characterization

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 (\u3bc-CT) can be adopted. \u3bc-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 \u3bc-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

Heat Flux Estimation in a Continuous Casting Mould by Inverse Heat Transfer Algorithms

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

Estimation of heat flux distribution in a continuous casting mould by inverse heat transfer algorithms - Paper No. DETC2011-47435

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

Microtomography-based CFD simulation of transport in open-cell aluminum metal foams

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

Estimation of Heat Flux Distribution in a Continuous Casting Mould by Inverse Heat Transfer Algorithms

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