Comparison and Analysis of Heat Transfer in Aluminum Foam Using Local Thermal Equilibrium or Nonequilibrium Model (original) (raw)
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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.
Local Thermal Non-Equilibrium Modelling of Convective Heat Transfer in High Porosity Metal Foams
2018
In this paper, forced convective heat transfer in a rectangular channel filled with aluminium metal foam and exposed to a constant heat flux is examined numerically with the thermal non-equilibrium assumption. A constant heat flux boundary condition is applied from the upper side of the channel. A numerical model is first validated with the available experimental results. Next, the effects of different configurations of metal foams with different porosities and different PPI values on fluid flow and heat transfer are examined. Results are given by average Nusselt number and pressure drop factor for different Reynolds numbers. A performance factor is also defined and the effect of different configurations on performance factor is comparatively examined. The results show that the heat transfer rate and pressure drop significantly depending upon Reynolds number, configuration and porosity.
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...
Thermal Convection Measurements inside Aluminum Foam and Comparison to Existing Analytical Solutions
Procedia Materials Science, 2014
Metal foams have high thermal conductivity and large surface area per unit volume. The internal structure of the foams promotes vigorous mixing of a moving fluid inside the foams. As such, metal foams are very suited for convection heat transfer designs. Clear models for forced convection heat transfer inside the foam, as well as reliable thermal measurements are indispensable for convection-based thermal system designs. This paper present direct experiment for Darcy airflow and fluid's temperature inside a heated aluminum cylinder filled with aluminum foam. The experimental fluid temperature is compared to the available analytical solutions for the two-equation model for fully-developed forced convection. Peculiar, physically-unexplainable behavior is displayed when plotting the existing analytical solution in the literature. An error was discovered and corrected. Good agreement is obtained with the correct solution.
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.
CFD Analysis of Conductive Heat Transfer in Different Porous Foams
2020
A very large number of computational models have already been proposed to evaluate thermal conductivity for high-porosity foams. Each and every approach considered different cellular morphologies and used different solution methods and all they have significant differences. Porous foams are generally used as insulators. So, the effective thermal conductivity of high porous materials, like polyvinyl chloride, expanded polystyrene, asbestos and fiberglass for various meshes are measured to determine the best porous foam that gives the best insulation. Then the results are compared between them and with the results of the previous investigations. It had been found out that effective thermal conductivity is inextricably related to porosity. Effective thermal conductivity decreases with the increasing of porosity such as for polyvinyl chloride, the value decreases from 0.56 to 0.43 for increasing the porosity from 0.75 to 0.95. Similar results are observed for other materials too.
Review of Performance Analysis of Aluminum Foams for Heat Transfer Augmentation
Performance analysis has been carried out to investigate the heat transfer characteristics from aluminium foam sample. The samples will be compared with the parallel plate fin heat transfer augmentation. The samples placed in a forced convection arrangement using a plate heater as a heat source and ambient air as the sink. A constant heat flux will be applied throughout the experiment with specific air velocity as a control parameter. The pore density of aluminium foam is varied in the range of the parameters 10, 20 & 40 pores per inches (PPI). Thermal performance of aluminium foam is evaluated in terms of the Nusselt number and thermal resistance of heat sinks. Further, the performance of each aluminium foam will be evaluated based on a compactness factor and power density.
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.
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.