One-dimensional heat transfer analysis in open-cell 10-ppi metal foam (original) (raw)
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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.
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...
2015
In this thesis analytical and numerical investigations of fluid flow and heat transfer through open cell metal foam heat exchangers are presented. Primarily, different representative unit cell approximations, i.e, tetrakaidecahedron, dodecahedron and cubic are discussed. By applying the thermal resistance analogy, a novel formulation for evaluation of the effective thermal conductivity of metal foams is proposed. The model improves previous models based on cubic or
Influence of pore density on thermal development in open-cell metal foam
Experimental Thermal and Fluid Science, 2017
Herein heat transfer measurements due to water flow in commercial open-cell aluminum foam confined by a cylindrical shell, which was heated by a constant heat flux, are described. Two kinds of commercial foam were tested: 10 and 40 pores per inch (ppi). Measurements included wall temperature along flow direction as well as average inlet and outlet temperatures of water. Flow rates ranged from Darcy to Forchheimer regimes. The wall temperature along the foam, as well as the local Nusselt number lucidly displayed thermal entry effects leading to thermal fully-developed ρ density (kg.m-3) Subscripts f fluid b bulk (mean) value e effective w wall Highlights • Nusselt numbers were obtained for Darcy and Forchheimer flows • Thermal entry length was determined and was significant for 10, 20 and 40 ppi • Thermal entry length differs from analytical predictions • Thermal entry length in metal foam is weak function of pore density
Thermal development in open-cell metal foam: An experiment with constant wall heat flux
International Journal of Heat and Mass Transfer, 2015
Experimental heat transfer results for a commercial open-cell aluminum foam cylinder heated at the wall by a constant heat flux and cooled by water flow, are presented. The results cover thermal-entry and fully-developed regions. Measurements include wall temperature along flow direction as well as average inlet and outlet temperatures of the water. Flow rates are in the Darcy and non-Darcy (transitional and Forchheimer) regimes. The wall temperature along the foam clearly shows two distinct behaviors related to thermally-developing and fully-developed conditions, which is confirmed by the behavior of local Nusselt number. The thermal entry length is determined and discussed in detail; it is also compared to its analytical counterpart for Darcy flow. The thermal entry region in metal foam is found to be significant and much longer than its analytically-predicted value. A method for estimating the bulk fluid temperature is envisioned for calculating the local Nusselt number. Previously undiscussed phenomenon is captured in the behavior of Nusselt number for non-Darcy regimes, which suggests periodic thermal development along the foam. The fully-developed data for the Darcy flow cases is compared to its analytical counterpart, and a correlation for the Nusselt number as a function of Reynolds number is proposed for non-Darcy flows.
International Journal of …, 2010
A 3D numerical simulation methodology for the flow and heat transfer at the pore scale level of high porosity open cell metal foam is presented. The pore scale topology is directly represented with a 3D numerical model of the geometry, which is discretised using a tetrahedral volume mesh for both its void and solid phases. The conjugate flow and temperature fields are obtained by solution of the Navier-Stokes and energy equations for two different foam pore densities under various flow and temperature conditions. Model validation is performed against macroscopic parameters such as pressure drop and heat transfer coefficient; the results are found in reasonable agreement with the experimental measurements.
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
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.
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.
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.