Thermal Transport in High Porosity Cellular Metal Foams

Zhao, C.Y.; Kim, T; Lu, Tian Jian; Hodson, H. P.

doi:10.2514/1.11780

Cited by 155 publications

(67 citation statements)

References 18 publications

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“…A fine scale structure thus tends to result in increased scattering and reduced transmission (see §3.3). Another effect of scale relates to the possibility of convection within or between pores [36][37][38]. It can readily be shown [2] that convective heat transfer within closed pores is only likely to be significant if they are very large (L>~10 mm).…”

Section: Scale Effects Convective Heat Transfer and Segmentation Cracksmentioning

confidence: 99%

Heat Transfer Through Plasma-Sprayed Thermal Barrier Coatings in Gas Turbines: A Review of Recent Work

2009

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A review is presented of how heat transfer takes place in plasma sprayed (zirconia-based) thermal barrier coatings (TBCs) during operation of gas turbines. These characteristics of TBCs are naturally of central importance to their function. Current state-of-the-art TBCs have relatively high levels of porosity (~15%) and the pore architecture (ie its morphology, connectivity and scale) has a strong influence on the heat flow. Contributions from convective, conductive and radiative heat transfer are considered, under a range of operating conditions, and the characteristics are illustrated with experimental data and modelling predictions. In fact, convective heat flow within TBCs usually makes a negligible contribution to the overall heat transfer through the coating, although what might be described as convection can be important if there are gross through-thickness defects such as segmentation cracks. Radiative heat transfer, on the other hand, can be significant within TBCs, depending on temperature and radiation scattering lengths, which in turn are sensitive to the grain structure and the pore architecture. Under most conditions of current interest, conductive heat transfer is largely predominant. However, it is not only conduction through solid ceramic that is important. Depending on the pore architecture, conduction through gas in the pores can play a significant role, particularly at the high gas pressures typically acting in gas turbines (although rarely applied in laboratory measurements of conductivity). The durability of the pore structure under service conditions is also of importance, and this review covers some recent work on how the pore architecture, and hence the conductivity, is affected by sintering phenomena. Some information is presented concerning the areas in which research and development work needs to be focussed if improvements in coating performance are to be achieved.

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Section: Scale Effects Convective Heat Transfer and Segmentation Cracksmentioning

confidence: 99%

Heat Transfer Through Plasma-Sprayed Thermal Barrier Coatings in Gas Turbines: A Review of Recent Work

2009

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“…Several investigations have been carried out for heat transfer in metal foams, but most have been restricted to single-phase heat transfer problems [20][21][22][23][24]. For solid/liquid phase change heat transfer in metal foams, there are only a few publications giving experimental test data for the latent thermal energy storage [18,25].…”

Section: Introductionmentioning

confidence: 99%

“…Metal foams [20,21], which have high strength-to-density ratio, ultralight porous structure and relatively high thermal conductivity, are believed to be a promising material for enhancing heat transfer performance and reducing the charging and discharging periods of PCMs. Several investigations have been carried out for heat transfer in metal foams, but most have been restricted to single-phase heat transfer problems [20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

A numerical investigation of heat transfer in phase change materials (PCMs) embedded in porous metals

YiShui

Zhao

2011

Energy

411

124

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The effects of metal foams on heat transfer enhancement in Phase Change Materials (PCMs) are investigated. The numerical investigation is based on the two-equation non-equilibrium heat transfer model, in which the coupled heat conduction and natural convection are considered at phase transition and liquid zones. The numerical results are validated by experimental data. The main findings of the investigation are that heat conduction rate is increased significantly by using metal foams, due to their high thermal conductivities, and that natural convection is suppressed owing to the large flow resistance in metal foams. In spite of this suppression caused by metal foams, the overall heat transfer performance is improved when metal foams are embedded into PCM; this implies that the enhancement of heat conduction offsets or exceeds the natural convection loss. The results indicate that for different metal foam samples, heat transfer rate can be further increased by using metal foams with smaller porosities and bigger pore densities. Keywords:Heat transfer enhancement; PCM; Metal foam; Thermal storage; Volume-averaged method; Non-thermal-equilibrium model.

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“…A fine-scale structure thus tends to result in increased scattering and reduced transmission. However, a potentially more significant effect of scale relates to the possibility of convection within or between pores (Lu et al 1998;Lu 1999;Zhao et al 2004). One possibility is that of recirculatory convection within closed pores.…”

Section: Heat Flow In Porous Materials (A ) Heat Flow Mechanismsmentioning

confidence: 99%

Porous materials for thermal management under extreme conditions

Clyne

Golosnoy

Tan

et al. 2005

Phil. Trans. R. Soc. A.

117

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A brief analysis is presented of how heat transfer takes place in porous materials of various types. The emphasis is on materials able to withstand extremes of temperature, gas pressure, irradiation, etc., i.e. metals and ceramics, rather than polymers. A primary aim is commonly to maximize either the thermal resistance (i.e. provide insulation) or the rate of thermal equilibration between the material and a fluid passing through it (i.e. to facilitate heat exchange). The main structural characteristics concern porosity (void content), anisotropy, pore connectivity and scale. The effect of scale is complex, since the permeability decreases as the structure is refined, but the interfacial area for fluid-solid heat exchange is, thereby, raised. The durability of the pore structure may also be an issue, with a possible disadvantage of finer scale structures being poor microstructural stability under service conditions. Finally, good mechanical properties may be required, since the development of thermal gradients, high fluid fluxes, etc. can generate substantial levels of stress. There are, thus, some complex interplays between service conditions, pore architecture/scale, fluid permeation characteristics, convective heat flow, thermal conduction and radiative heat transfer. Such interplays are illustrated with reference to three examples: (i) a thermal barrier coating in a gas turbine engine; (ii) a Space Shuttle tile; and (iii) a Stirling engine heat exchanger. Highly porous, permeable materials are often made by bonding fibres together into a network structure and much of the analysis presented here is oriented towards such materials.

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Thermal Transport in High Porosity Cellular Metal Foams

Cited by 155 publications

References 18 publications

Heat Transfer Through Plasma-Sprayed Thermal Barrier Coatings in Gas Turbines: A Review of Recent Work

Heat Transfer Through Plasma-Sprayed Thermal Barrier Coatings in Gas Turbines: A Review of Recent Work

A numerical investigation of heat transfer in phase change materials (PCMs) embedded in porous metals

Porous materials for thermal management under extreme conditions

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