Proceedings of metal foams (original) (raw)
Related papers
Characterization Of The Heat TransferIn Open-cell Metal Foam
WIT Transactions on the Built Environment, 2004
The material characterization of open-cell aluminum foam in terms of heat transfer is presented. A one-dimensional heat transfer model for the combined convection and conduction in the foam is summarized. The model uses the foam parameters that are usually reported by the manufactures such as: the surface area, the relative densities, the ligament diameters and number of pores per inch. The model predicts the temperature profile in the foam. The model was applied successfully to a sample of aluminum foam having ten pores per inch and was verified by direct experiment. Excellent agreement between the predictions of the model and the experimental data was obtained. The assumption of a onedimensional heat transfer was validated. The effect of the air flow rate on the heat transfer is also studied in order to further characterize the heat transfer behavior of the foam. The results for an aluminum foam sample of 10 pores per inch are presented at these flow rates.
Foam height effects on heat transfer performance of 20 ppi aluminum foams
Applied Thermal Engineering, 2012
This paper investigates the heat transfer performance of two 20 PPI (pores per linear inch) aluminum foams with constant porosity (around 0.93) and different foam core height (20 mm and 40 mm). The aluminum foams are cellular structure materials that present a stochastic interconnected pores distribution mostly uniform in size and shape. Most commercially available metal foams are based on aluminum, copper, nickel and metal alloys. Metal foams have considerable applications in multifunctional heat exchangers, cryogenics, combustion chambers, cladding on buildings, strain isolation, petroleum reservoirs, compact heat exchangers for airborne equipment, air cooled condensers and compact heat sinks for power electronics. The experimental measurements of the heat transfer coefficient and pressure drop have been carried out in a test apparatus built at Dipartimento di Fisica Tecnica of the Università di Padova. The foam core height effects on the heat transfer performance have been studied imposing three constant specific heat fluxes at the bottom of the samples: 25.0, 32.5 and 40.0 kW m À2 and varying the frontal air velocity between 2.0 and 5.0 m s À1 . The experimental heat transfer coefficients and pressure gradients have been compared against the predictions obtained from two models recently suggested by present authors.
Metal foams as novel materials for air-cooling heat exchangers
2012
High-porosity metal foams have thermal, mechanical, electrical, and acoustic properties making them attractive for various engineering applications. Due to their large surface-area-to-volume ratio, tortuous flow path, and relatively high thermal conductivity they are being considered for a range of heat transfer applications. In this experimental study, open-cell aluminum metal foam is considered as a replacement for conventional louvered fins in brazed-aluminum heat exchangers. Closed-loop wind tunnel experiments are conducted to measure the pressure drop and heat transfer performance of metal-foam heat exchangers. In addition to characterizing the air-side pressure-drop and heat transfer performance, issues related to condensate drainage and frost formation are considered. The main performance obstacle for the application of metal foams is the relatively high pressure drop occurring for velocities typical to air-cooling applications. This high pressure drop results in larger air-side fan power requirements if metal foams are used as a "drop-in replacement" for louver fins. On the other hand, the heat transfer performance of the metal foams far surpasses that of conventional louvered fins, reaching two to three times the heat transfer coefficient of conventional fins. Smaller pore sizes provide larger surface area per unit volume and enhanced mixing, resulting in higher heat transfer. This excellent heat transfer performance means that alternate deployments of the metal foam are possible to manage fan power, while achieving comparable thermal performance. The experimental data are presented in terms of friction factors and Colburn j factors, and design correlations are developed to predict heat exchanger performance. Under wet-surface conditions, water retention can be an important problem for louvered-fin operation. Surprisingly, metal foams have water drainage behavior superior to that of conventional fins. The effects of geometry, porosity, surface treatment, and orientation on water drainage have been analyzed. iii ACKNOWLEDGEMENT I am heartily thankful to my supervisor, Professor Anthony Jacobi, whose encouragement, guidance and support from the initial to the final level enabled me to develop an understanding of the subject. I offer my regards and blessings to all of those who supported me in any respect during the completion of the project. I am grateful to Zhengshu Dia, Prof.Chen Qi, Prof.Young-Gil Park and Jessica Bock for their help and suggestions. I would like to show my gratitude to ARTI (Air Conditioning and Refrigeration Technology Institute) for financing the project. Lastly, I am thankful to my mother and sisters for their help. Kashif Nawaz iv TABLE OF CONTENTS Chapter 1: Water retention behavior of aluminum metal foams…………... 1 1.1. Introduction..………………………………………………………… 1 1.2. Dynamic dip testing of open-cell metal foams...…………………….. 5 1.3. Conclusion…………………………………………………………... 1.4 References ……………………………………………………………. Chapter 2: Pressure drop for air flow through open-cell foams…………. 14 2.1. Introduction…………………………………………………………. 14 2.2. Experimental results………………………………………………… 2.3. Modeling the pressure drop performance…………………………… 39 2.4. Conclusion…………………………………………………………... 2.5. References…………………………………………………………… 50 Chapter 3: Heat transfer performance of metal foams ……….………….. 56 3.1. Introduction………………………………………………………….. 56 3.2. Experimental results…………………………………………………. 3.3. Modeling the heat transfer performance.……………………………. 77 3.4. Conclusion…………………………………………………………… 3.5. References……………………………………………………………. 83 Appendix A: Sample manufacturing……………………………………...
Forced-Convection Measurements in the Fully Developed and Exit Regions of Open-Cell Metal Foam
Transport in Porous Media, 2015
Experimental heat transfer data for water flow in commercial, open-cellaluminum-foam cylinder heated at the wall by a constant heat flux, are presented. The measurements include wall temperature along flow direction as well as average inlet and outlet temperatures of the water. Flow speeds were in the Darcy and non-Darcy (transitional and Forchheimer) regimes. Heat fluxes were 14,998 and 26,347 W/m 2 for the Darcy and non-Darcy regimes, respectively. Measurements were focused on the thermally fully developed and an anticipated exit regions, with the latter region being often ignored in the literature. The experimental Nusselt number for the Darcy flow cases is compared to its analytical counterpart. A comparison shows good agreement, considering the approximations involved in the analytical solution and experimental errors. Previously unpublished phenomenon is presented in the behavior of Nusselt number for non-Darcy regimes. The experimental results and measuring technique can be used for validation of other analytical and numerical solutions, as well as in testing heat-exchange engineering designs based on metal foam. Keywords Metal foam • Convection • Fully developed • Exit region • Experiment • Water List of symbols A Cross-sectional area (m 2) k Thermal conductivity (W m −1 K −1) Nu Nusselt number q Heat flux (W m −2) T Temperature (• C) u Flow velocity (m s −1) B Nihad Dukhan
Experimental Fully-Developed Thermal Convection for Non-Darcy Water Flow in Metal Foam
Journal of Thermal Engineering, 2016
Experimental heat transfer data for water flow in commercial open-cell aluminum foam cylinder heated at the wall by a constant heat flux, is presented. The foam had 20 pores per inch (ppi) and a porosity of 87%. The measurements included wall temperature along flow direction as well as average inlet and outlet temperatures of the water. Flow speeds were in the non-Darcy regimes (transitional and Forchheimer). Heat fluxes were 14,998 W/m 2 and 26,347 W/m 2. The behavior of the wall temperature clearly shows thermal fully-developed conditions. The experimental Nusselt number is presented as a function of axial distance in flow direction, and showed what seemed to be a periodic development. A correlation for the average Nusselt number as a function of flow Reynolds number is provided. The experimental data can be used for validation of other analytical solutions, numerical models and heat-exchange engineering designs based on metal foam.
The effect of the cooling performance of a copper metal foam heat sink under buoyancy-induced convection is investigated in this work. Experiments are conducted on copper metal foam of 61.3% porosity with 20 pores per inch. The pressure drop experiment is carried out to find the permeability and foam coefficient of the porous media. It is found that the property of porous media changes by changing the angle of inclination of the porous media from a horizontal to a vertical position while keeping the orientation and porosity the same. The Hazen-Dupuit Darcy model is used to curve-fit the longitudinal global pressure drop versus the average fluid speed data from an isothermal steady-flow experiment across the test section of the porous medium. The study concludes that the permeability and foam coefficient for copper foam is found to be 1.11 × 10−7 m2 and 79.9 m−1, respectively. The heat transfer study shows that the thermal performance of copper metal foam is 35–40% higher than the conventional aluminum metal heat sink under an actual conventional mode.
Thermal-hydraulic performance of metal foam heat exchangers under dry operating conditions
Applied Thermal Engineering, 2017
Due to their large surface-area-to-volume ratio and tortuous structure, metal foams hold promise for heat transfer applications. Both of these factors increase the heat transfer by enhancing the mixing and surface area. The main disadvantage associated with their thermal-hydraulic performance is relatively higher pressure drop, resulting in larger pumping power requirements if they are used in a heat exchanger. In this paper, open-cell aluminum metal foam is considered as a highly compact replacement for conventional fins in brazed aluminum heat exchangers. SEM techniques are used to characterize the foam characteristics such as pore and ligament diameter. Experiments are conducted by a closed-loop wind tunnel to measure the pressure drop and heat transfer rates. The effects of different porosity, fin depth, bonding method, base metal, condensation and frost are considered. It is found that incorporating foam with smaller pores results in larger pressure drop per unit length but the heat transfer rate is higher as well. Fin depth can be changed as well to reduce the pressure drop. Furthermore, metal foams, found to perform much better compared to other designs employing plain fins or louver fins with much larger heat transfer coefficients. Permeability and inertia coefficients are determined and compared with the reported data. An appropriate length scale is suggested for the data reduction. Based on the experimental findings, a model has been developed relating the foam characteristics and flow conditions to the pressure drop and heat transfer.
As a new-type extending surface, metal foam owns great potential in next generation heat transfer technologies. Convective heat transfer performance in metal foams is numerically investigated based on the local thermal equilibrium (LTE) model and the local thermal non-equilibrium (LTNE) model. The solid efluid temperature difference and relative deviation are put forward for quantifying LTNE effect. The effects of basic parameters on heat transfer are analysed in depth and the LTNE conditions in metal-foam tube for efficient heat exchangers are summarized. It is indicated that the relative deviation is a more suitable criterion for LTNE effect in metal foam than the solidefluid temperature difference. The LTNE effect in metal foam is conspicuous for low porosity, large fluidesolid thermal conductivity difference, small duct size, low pore density, and low Reynolds number. Measures lowering proportion of local convective thermal resistance in total thermal resistance, or the ratio of thermal resistance of solid to that of fluid can weaken LTNE effect in metal foam. There is no necessary relationship between thermal performance of metal-foam heat exchangers and corresponding LTNE effect. Clarifying LTNE conditions in porous foams can lay a foundation for the demarcating criterion of LTE/LTNE models. This can also guide quick and accurate thermal design and verification of metal-foam heat exchangers.
Experimental air heat transfer and pressure drop through copper foams
Experimental Thermal and Fluid Science, 2012
This paper presents experimental heat transfer coefficient and pressure drop measurements carried out during air forced convection through five different copper foam samples. The specimens present a different number of pores per inch: 5, 10, 20, and 40 PPI and different porosities, which vary between 0.905 and 0.934. The tests were run by varying the air mass flow rate in the range between 0.006 and 0.012 kg s À1 , which corresponds to the air frontal velocity from 2.5 to 5 m s À1 . Two different heat fluxes, imposed by means of an electrical heater were investigated: 25.0 and 32.5 kW m À2 . The collected heat transfer and pressure drop data were analyzed to obtain the global heat transfer coefficient, the normalized mean wall temperature, the pressure gradient, permeability, inertia coefficient, and drag coefficient. The experimental heat transfer measurements reported in the present work increase the knowledge in heat transfer and fluid flow in metal foams.