Ultralight porous metals: From fundamentals to applications

Lu, Tianjian

doi:10.1007/bf02486571

Cited by 71 publications

(15 citation statements)

References 34 publications

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“…High porosity metal foams are usually porous media with low density and novel structural and thermal properties (Tianjian [13]). They offer light weight, high rigidity and strength, and high surface area, which make them able to recycle heat efficiently.…”

Section: Introductionmentioning

confidence: 99%

Rotating metal foam structures for performance enhancement of double-pipe heat exchangers

Alhusseny

Turan

Nasser

2017

International Journal of Heat and Mass Transfer

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In order to enhance the amount of heat transported in a double-pipe heat exchanger, a compound enhancement is proposed incorporating both active and passive methods. The first one is through introducing secondary flows in the vicinity of the conducting surface using metal foam guiding vanes, which are fixed obliquely and rotating coaxially to trap fluid particles while rotation and then force them to flow over the conducting surface. The other is via covering the conducting surface between the two pipes with a metal foam layer to improve the heat conductance across it. This proposal is examined numerically by studying the three-dimensional, steady, incompressible, and laminar convective fluid flow in a counter-flow double-pipe heat exchanger partially filled with high porosity metal foam and rotating coaxially. With regards to the influence of rotation, both the centrifugal buoyancy and Coriolis forces are considered in the current study. The generalised model is used to mathematically simulate the momentum equations in the porous regions. Moreover, thermal dispersion has been taken into account while considering that fluid and solid phases are in a local thermal non-equilibrium. Computations are performed for a wide range of design parameters influencing the performance achieved such as the operating conditions, the configuration of the guiding vanes utilized, and the geometrical and thermal characteristics of the metal foam utilised. The results are presented by means of the heat exchanger effectiveness, pressure drop, and the overall system performance. The current proposed design has effectively proved its potential to enhance the heat transported considerably in view of the significant savings in the pumping power required compared to the heat exchangers fully filled with metal foams. Furthermore, the data obtained reveal an obvious impact of the design parameters inspected on both the heat exchanged and the pressure loss; and hence, the overall performance obtained. Although the heat exchanger effectiveness can be improved considerably by manipulating the design factors, care must be taken to avoid unnecessary expenses resulted from potential increases in pressure drop. KEYWORDS: Heat Exchanger, Compound Enhancement, Metal Foams, Rotation, Overall PerformanceNomenclature asf solid-to-fluid interfacial specific surface area cp specific heat of fluid phase Cc cold stream heat-capacity rate Cc = ṁc cp,c Ch cold stream heat-capacity rate Ch = ṁh cp,h Cmin the smaller of the hot (Ch) and the cold (Cc) fluid-phase heat-capacity rates df fiber diameter dp pore diameter Da Darcy number, Da=K / Dh 2 Dh hydraulic diameter of the channel Di1, Di2 internal and external diameters of the inner annular tube Do1, Do2 internal and external diameters of the outer annular tube F inertial coefficient hsf solid-to-fluid interfacial specific heat transfer coefficient Hsf dimensionless solid-to-fluid interfacial specific heat transfer coefficient k thermal conductivity K permeability of the porous medium

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Section: Introductionmentioning

confidence: 99%

Rotating metal foam structures for performance enhancement of double-pipe heat exchangers

Alhusseny

Turan

Nasser

2017

International Journal of Heat and Mass Transfer

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“…High porosity metal foams are usually porous media with low density and novel structural and thermal properties Tianjian [9]. They offer light weight, high rigidity and strength, and high surface area, which make them able to recycle energy efficiently.…”

Section: Introductionmentioning

confidence: 99%

“…(3,4,5,6,7,10,12,13,14,15), medium porosity has been varied from 0.89 to 0.97 as shown in Figs. (6,9,10,12,13,14), pore density (5PPI≤ω≤40PPI) as shown in Figs. (6,7,8,9,10), solid to fluid-phase thermal conductivity ratio (250≤κ≤4000) as shown in Fig.…”

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Developing convective flow in a square channel partially filled with a high porosity metal foam and rotating in a parallel-mode

Alhusseny

Turan

Nasser

2015

International Journal of Heat and Mass Transfer

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The development of three-dimensional heat transfer and fluid flow in a square channel rotating in a parallel-mode has been investigated numerically. The duct is partially occupied by a foam material of high porosity ε≥0.89 and subjected to a uniform wall heat flux. In regards to the influence of rotation, both the centrifugal buoyancy and Coriolis forces are considered in the current study. The generalised model is used to mathematically simulate the momentum equations employing the Boussinesq approximation for the density variation. Moreover, thermal dispersion has been taken into account with considering that fluid and solid phases are in a local thermal non-equilibrium. The governing equations are discretised according to the finite volume method with employing a hybrid differencing scheme. Computations are performed for a wide range of parameters including the hollow ratio (0≤S≤1), foam porosity (0.89≤ε≤0.97), pore density (5PPI≤ω≤40PPI), solid to fluid thermal conductivity ratio (250≤κ≤4000), Reynolds number (250≤Re≤2000), and rotation number (0≤Ro≤1), while the values of characteristic temperature difference and Prandtl numbers are maintained constant at ΔTc=1000°C and Pr=0.7, respectively. Results reveal that flow resistance and heat transport are augmented with either decreasing the hollow ratio and foam porosity or increasing Reynolds and rotation numbers, while two contradictory trends are found for the impact of increasing pore density on heat transfer; either enhancing or suppressing depending on the size of hollow zone. In addition, both rotation and thermal dispersion have dominant roles in enhancing heat transfer at the higher levels of porosity or the lower values of conductivity ratios. However, these roles are reduced gradually with decreasing the foam porosity or increasing thermal conductivity ratio, but do not completely vanish. Eventually, the worth of using high porosity fibrous media in enhancing the heat transported through rotating channels has been inspected. An overall enhancement parameter is compared for the current study with a previous work regarding turbulent flow in a rotating clear channel, where it has been confirmed that the current proposal is practically justified and efficient. 06-05-2015Ahmed Alhusseny A5, George Begg Building, Sackville Street Manchester, M60 1QD (+44) 7876340153 ahmed.alhusseny@postgrad.manchester.ac.uk International Journal of Heat and Mass TransferThe current research presents a numerical simulation of the three-dimensional fluid flow and heat transfer in a square channel rotating around a parallel axis. The duct is partially occupied by metal foam of high porosity (ε≥ 0.89) and subjected to a uniform wall heat flux. Both the centrifugal buoyancy effect and Coriolis forces are considered regarding to the rotation effect in the current study.The generalised model is used to mathematically simulate the momentum equations employing the Boussinesq approximation for the density variation. Moreover, thermal dispersion has been taken into account w...

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“…The mechanical strength, stiffness, and energy absorption of foam-covered cylinders made them very popular for industrial applications as biomedical implants [45] as well as heat exchangers [46] which are the main focus of this study. Their higher heat transfer performance compare to the similar available options has been well-recorded in a number of studies.…”

Section: Metal Foam Application In Heat Exchangermentioning

confidence: 99%

Wake behind a rough (metal foam-covered) cylinder in cross-flow

Abdi¹

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The flow structures behind a circular cylinder are associated with various instabilities. These instabilities are characterized by the Reynolds number and they include the wake, separated shear layer and boundary layer. Depending on the physical application of the cylinder, increasing the level of turbulence by wrapping the cylinder with metal foam would be a target for drag reduction or heat transfer enhancement.In contrast to the extensive consideration that has been devoted to the flow around bare cylinders, the flow structures around the foam-covered cylinders and the characteristics of the wake behind such surfaces has received relatively little attention. Since the present study explores the possibility of using metal foams as replacements for fins on heat exchanger tubes, investigation on the flow-field structures downstream of a foam-covered cylinder and compare it to the bare cylinder specifies the feasibility of using the foamcovered cylinders in heat exchangers. Moreover, the outcome of this study can be used to develop an appropriate boundary condition for the porous-air interface modelling also increases the knowledge of turbulence in porous media.As it will be discussed more in detail in the following chapters, pressure drop and drag coefficient are directly linked to the wake and recirculation region, and to study these two phenomena, it is necessary to have in depth study on the flow-field down-stream of the cylinder. Hence, the purpose of this study is to investigate the wake region behind a foam- Moreover, using hot-wire anemometry, to investigate the energy of the flow inside and outside of the foam-covered cylinder's wake, let us know if a foam-covered cylinder can be treated as an obstacle to the incident flow with a rough surface or the whole foam can be considered as the combination of local jets that are coming out of the pores and disperse in random directions.III

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Ultralight porous metals: From fundamentals to applications

Cited by 71 publications

References 34 publications

Rotating metal foam structures for performance enhancement of double-pipe heat exchangers

Rotating metal foam structures for performance enhancement of double-pipe heat exchangers

Developing convective flow in a square channel partially filled with a high porosity metal foam and rotating in a parallel-mode

Wake behind a rough (metal foam-covered) cylinder in cross-flow

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