Review of Performance Analysis of Aluminum Foams for Heat Transfer Augmentation (original) (raw)
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The Development of Aluminium Foams for Enhanced Heat Transfer
2017
A novel replication technique for the production of open-celled aluminium foam has recently been devised and is undergoing commercial development by the company Constellium. The technique allows close control over the pore size and shape; a feature that is uncharacteristic of metal foam production methods in general and control to such an extent is unprecedented. The method provides an excellent pathway for the exploration of pore geometry/heat transfer behaviour relations, which is the objective of this study. This also aligns with the commercial goals of Constellium as heat transfer applications have been identified as a key market for their foams. Based on the technique; the focus of this work was the development of a laboratory protocol to allow the production of aluminium foam samples with a range of different mesostructures. The heat transfer behaviour, including permeability, of foams with differing matrix metal, pore size, pore aspect ratio and pore shape were examined under forced convection conditions. Decreasing pore size was found to provide enhanced heat transfer, although for pores <3mm the benefit was outweighed by a large decrease in permeability. Small changes in pore shape as a result of preform compaction during processing may be exploited to provide improved heat transfer without reducing permeability. Elongation of pores provided no enhancement of heat transfer or permeability.
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.
Performance of Aluminum and Carbon Foams for Air Side Heat Transfer Augmentation
Journal of Heat Transfer, 2010
The air side heat transfer performance of three aluminum foam samples and three modified carbon foam samples are examined for comparison with multilouvered fins often found in compact heat exchangers. The aluminum foam samples have a bulk density of 216 kg/ m 3 with pore sizes of 0.5, 1, and 2 mm. The modified carbon foam samples have bulk densities of 284, 317, and 400 kg/ m 3 and machined flow passages of 3.2 mm in diameter. The samples were placed in a forced convection arrangement using a foil heater as the heat source and ambient air as the sink. A constant heat flux of 9.77 kW/ m 2 is applied throughout the experiments with the mean air velocity ranging from 1 to 6 m/s as the control parameter. The steady volume-averaged momentum equation and a twoequation nonequilibrium heat transfer model are employed to extract the volumetric heat transfer coefficients. Pressure drop measurements are correlated with the Darcy-Forcheimer relation. Empirical heat transfer correlations for the aluminum and carbon foam samples are provided. Using a hypothetical heat exchanger considering only the thermal resistance between the ambient air and the outer tube wall, the air side performance for each sample is modeled based on the local heat transfer coefficients and friction factors obtained from experiments. The performance of each sample is evaluated based on a coefficient of performance (COP, defined as the ratio of the total heat removed to the electrical input of the blower), compactness factor (CF, defined as the total heat removed per unit volume), and power density (PD, defined as the total heat removed per unit mass). Results show the carbon foam samples provide significant improvement in CF but the COP and PD are considerably lower than that for comparable multilouvered fin heat exchangers.
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.
Heat Transfer Engineering, 2015
Aluminum foams are favorable in modern thermal engineering applications because of the high thermal conductivity and the large specific surface area. The present study is to investigate an application of a porous aluminum foam by using local thermal equilibrium (LTE) and local thermal non-equilibrium (LTNE) heat transfer models. Threedimensional simulations of laminar flow (for porous foam zone), turbulent flow (for open zone) and heat transfer are performed by a computational fluid dynamics (CFD) approach. Meanwhile, the Forchheimer extended Darcy's law is employed for evaluating the fluid characteristics. The simulation results are compared with the experimental data in the literature. By comparing and analyzing the local and average Nusselt number, it is found that the LTNE and LTE models can obtain the same Nusselt numbers inside the aluminum foam when the air velocity is high, meaning that the aluminum foam is in a thermal equilibrium state. Besides that, a low interfacial heat transfer coefficient is required for the aluminum foam to reach a thermal equilibrium state as the height of the aluminum foam is increased. This study suggests that the LTE model could be applied to predict the thermal performance for the high fluid velocity case or for the case with large height.
2016
In this paper an experimental investigation on forced convection in a compact heat exchanger made up with an aluminum foam plate of 212.5mm x 212.5mm with a thickness of 40 mm and a single array with five circular tubes is presented. The foam has a porosity of 0.93 with 10, 20 and 30 pores per inch and the tubes in aluminum have internal and external diameters equal to 9.5 mm and 12.5 mm. The test rig consists of an open air channel and a closed water cycle and the aluminum foam plate is placed inside the channel. The performances of the compact heat exchanger are evaluated for assigned hot water mass flow rate and different hot water inlet temperatures and air mass flow rate. Results are given in terms of heat transfer rates and pressure drops as a function of air velocity and Reynolds numbers. The evaluation of dimensionless, Colburn factor and Nusselt number is performed for different air mass flow rates and hot water inlet temperatures.
Numerical Investigation on Thermal and Fluid Dynamic Behaviors of Heat Exchanger in Aluminium Foam
International Heat Transfer Conference 16, 2018
Designers of heat exchangers are regularly searching for new methods that enhance the heat transfer efficiency. A possible substitute of the conventional fins is the use of open-cell metal foams. Low density, good rigidity, high thermal conductivity and huge value of surface/volume ratio represent the best characteristics of porous media. For these features, metal foams are used in several applications such as heat exchangers, fuel cells, heat sinks and solar thermal plants. The need to create new systems in reduced volumes led to the adoption of the aluminum foams for their great specific area surface that allows to have compact heat exchanger characterized by a high thermal performance. A numerical investigation has been accomplished to analyze the thermal and fluid dynamic behavior of a tubular heat exchanger partially filled with aluminum foam. The Darcy-Brinkman-Forchheimer flow model and the thermal non-equilibrium model (LTNE) for the energy are applied to carry out two-dimensional simulations on the metal foam heat exchanger. The foam has a porosity and (number) pores per inch respectively equal to 0.935 and 20. The heat exchanger is analyzed for different air flow rates and a fixed surface tube temperature. The results are given as average and local heat transfer coefficient evaluated on the external surface of the tubes. Furthermore, the local air temperature profiles in the smaller cross section, between two consecutive tubes are given. Finally, the Energy Performance Ratio (EPR) is evaluated in order to demonstrate the thickness of metal foam that improve the system performances.
Experimental and numerical analysis of one dimensional heat transfer on open cell aluminum foams
Gazi University Journal of Science
In this study, one dimensional heat transfer of open cell aluminum metal foams is investigated both experimentally and by using numerical methods as well. Open cell aluminum foams with pore densities of 10, 20 and 30 (Number of Pores Per Inch) PPI were shaped into heat exchangers. The foams having sizes of 200 × 100 × 20 mm were insulated on their three faces. Steady heat flux was maintained on the base section of the foam by heating a plate shaped coil electrically. Temperature distributions on the vertical sections and mostly on locations near heaters were measured with the thermocouples located on the aluminum foams. With the help of the recorded temperatures from the tests the graphs of open cell aluminum foams with pore densities of 10, 20 and 30 were plotted. First of all, one dimensional heat transfer equations were derived for the numerical solution of the system. The governing equations obtained were then discretized by using the Central Difference Method and finally solved...
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……………………………………...