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

Airflow measurement across negatively infiltration processed porous aluminum structures

Detailed structural characterization and experimental measurement of airflow across open-celled aluminum foam structures with near-spherical cells varying in pore sizes and interstices are presented herein. The aluminum foam structures were produced by infiltrating liquid aluminum into convergent gaps created by packed beds of near-spherical hydrosoft salt beds varying in particle sizes, packing densities, and infiltration pressures. A quantitative assessment of the unit pressure drops developed across these structures show that viscous and inertial terms of these structures were observed to greatly depend on the shape and structural macroscopic parameters of the porous medium. © 2019 American Institute of Chemical Engineers AIChE J, 2019. © 2019 American Institute of Chemical Engineer

CFD study on thermal transport in open-cell metal foams with and without a washcoat: Effective thermal conductivity and gas-solid interfacial heat transfer

publisher: Elsevier articletitle: CFD study on thermal transport in open-cell metal foams with and without a washcoat: Effective thermal conductivity and gas-solid interfacial heat transfer journaltitle: Chemical Engineering Science articlelink: http://dx.doi.org/10.1016/j.ces.2016.12.006 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: CFD study on thermal transport in open-cell metal foams with and without a washcoat: Effective thermal conductivity and gas-solid interfacial heat transfer journaltitle: Chemical Engineering Science articlelink: http://dx.doi.org/10.1016/j.ces.2016.12.006 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: CFD study on thermal transport in open-cell metal foams with and without a washcoat: Effective thermal conductivity and gas-solid interfacial heat transfer journaltitle: Chemical Engineering Science articlelink: http://dx.doi.org/10.1016/j.ces.2016.12.006 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved.This work was supported by the National Natural Science Foundation of China (No. 51276181, 21306192) and the National Key Research and Development Program – China (2016YFB0601203)

Model Optimasi Integer Campuran Untuk Persoalan Multi-Tahap Mean-Varians Pasca-Pajak (Post-Tax)

Mixed Integer Programming Model approach to portfolio adjustment post tax with mean-variance approach needs to be understood because it is very useful in the preparation of various levels of investment multistage and when the general re- turns of the value of all assets. Uncertainty in return on assets is made in the form of scenario tree. Risk between scenarios using a probabilistic approach of classical stochastic programming. Tax rules that have been set will be peering with Mixed Integer Programming Model for the problem of multistage mean-variance and then used to calculate all taxes with a portfolio of multi-phase upon return of assets in the hope of an efficient risk. Incorporation of risk in the model will cause the strength and the difference between the assets owned by the owner of an asset combined with a single asset owners at the time of return. General Returns and risk aversion can have an effect on the distribution of assets to the broker. Calculation results are presented with different scenarios using the tree in order to show a comparison of the results of all the models. Tax rules are based on the mixed integer optimization model is used to generate all kinds of portfolios in various levels of tax administration. The results of calculations on the model is tested using a case study with a different scenario. Seen that the optimal portfolios generated by mixed integer optimization model mean-variance.Pendekatan Model Pemrograman integer Campuran untuk pengaturan protofolio pasca pajak (post tax) dengan mean-varians perlu dipahami karena Pendekatan ini sangat berguna dalam penyusunan berbagai tingkatan investasi (multistage) dan pada saat pengembalian umum dari nilai semua aktiva. Ketidakpastian pada pengembalian aktiva dibuat dalam bentuk pohon skenario (scenario tree). Resiko (penyusutan aktiva) antara skenario menggunakan suatu pendekatan probabilis- tik dari pemrograman stokastik klasik. Peraturan pajak yang telah ditentukan akan dilakukan pengabungan dengan Model Pemrograman integer Campuran un- tuk persoalan multi-tahap mean-varians kemudian digunakan untuk menghitung semua pajak dengan portofolio multi-tahap pada saat pengembalian aktiva de- ngan harapan resiko yang efesien. Penggabungan resiko pada model tersebut akan menyebabkan kekuatan dan perbedaan aktiva yang dimiliki antara pemilik aktiva (asset) gabungan dengan pemilik aktiva tunggal pada saat pengembalian. Pengembalian umum dan risk aversion (penolakan atas kehilangan aktiva) dapat berefek pada distribusi aktiva (asset) kepada broker. Hasil perhitungan disajikan dengan menggunakan pohon skenario yang berbeda agar dapat menunjukkan per- bandingan hasil dari semua model. Peraturan pajak yang berdasarkan kepa- da model optimasi integer campuran digunakan untuk menghasikan semua jenis portofolio pemberian pajak diberbagai tingkatan. Hasil perhitungan pada mo- del ini diuji dengan menggunakan studi kasus dengan skenario berbeda. Terlihat bahwa portofolio yang optimal dihasilkan oleh model optimasi integer campuran mean-varians.53 HalamanTesis Magiste

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

On the effective thermal conductivity of metal foams

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 (\u3bc-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 \u3bc-CT \u2013 CFD coupling at the pore level will be illustrated

Macroscopic and Multi-Scale Models for Multi-Class Vehicular Dynamics with Uneven Space Occupancy: A Case Study

In this paper, we propose two models describing the dynamics of heavy and light vehicles on a road network, taking into account the interactions between the two classes. The models are tailored for two-lane highways where heavy vehicles cannot overtake. This means that heavy vehicles cannot saturate the whole road space, while light vehicles can. In these conditions, the creeping phenomenon can appear, i.e., one class of vehicles can proceed even if the other class has reached the maximal density. The first model we propose couples two first-order macroscopic LWR models, while the second model couples a second-order microscopic follow-the-leader model with a first-order macroscopic LWR model. Numerical results show that both models are able to catch some second-order (inertial) phenomena such as stop and go waves. Models are calibrated by means of real data measured by fixed sensors placed along the A4 Italian highway Trieste–Venice and its branches, provided by Autovie Venete S.p.A.</jats:p

High resolution microtomography-based CFD simulation of flow and heat transfer in aluminum metal foams

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 (m-CT) technique can be adopted. In this work, the results of high resolution m-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 m-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

Microtomography-based CFD Analysis of Transport in Open-Cell Aluminum Metal Foams

3Nowadays, 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.nonemixedRanut, Paola; Nobile, Enrico; Mancini, LuciaRanut, Paola; Nobile, Enrico; Mancini, Luci

High resolution X-ray microtomography-based CFD simulation for the characterization of flow permeability and effective thermal conductivity of aluminum metal foams

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\u201320\u201330 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)