Thermal Convection Measurements inside Aluminum Foam and Comparison to Existing Analytical Solutions (original) (raw)
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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.
Materials, 2017
In this paper, the heat transfer performances of aluminum metal foams, placed on horizontal plane surface, was evaluated in forced convection conditions. Three different types of contacts between the sample and the heated base plate have been investigated: simple contact, brazed contact and grease paste contact. First, in order to perform the study, an ad hoc experimental setup was built. Second, the value of thermal contact resistance was estimated. The results show that both the use of a conductive paste and the brazing contact, realized by means of a copper electro-deposition, allows a great reduction of the global thermal resistance, increasing de facto the global heat transfer coefficient of almost 80%, compared to the simple contact case. Finally, it was shown that, while the contribution of thermal resistance is negligible for the cases of brazed and grease paste contact, it is significantly high for the case of simple contact.
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
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.
Chemical Engineering Communications
Combined convection heat transfer and fluid flow around a circular cylinder surface placed in open-cell aluminum foams and subjected to constant heat flux inside a rectangular, water-filled horizontal channel was numerically and experimentally studied. Two models (rectangular and trapezoidal open-cell aluminum foam shapes) made of 6101-T6 alloy with pore densities of 10 and 40 pores per linear inch (PPI) and 7–9% relative density were employed as test sections. The aluminum foam dimensions were 35.7 × 35.7 × 36.85 mm, the Reynolds number range was 60–2000, and the modified Grashof number range was 2 × 102–2.6 × 107. Governing equations (continuity, momentum, and energy) were solved using the finite-volume method (FVM). Effects of the porous characteristics of aluminum foams and mixed convection heat transfer parameters on buoyancy force, Nusselt number, friction factor, and pumping power values of the two models were investigated. The results show that high mixed convection occurred...
Experimental Measurements Of Air Forced Convection Through Copper Foams
2012
This paper aims at investigating the air heat transfer and fluid flow through open-cells copper foam samples with different number of pores per unit of length (PPI) with constant porosity (ε=0.93) and foam core height of 40 mm. The experimental heat transfer coefficient and pressure drop measurements were carried out during air forced convection through electrically heated copper foams; the data points are collected in a dedicated test rig. The experimental measurements permit to understand the effects of the pore density on the heat transfer and fluid flow performance of the foams. Present data relative to copper foam samples are compared against present authors experimental measurements for 40 mm high aluminum foams at the same operative test conditions. The paper presents experimental heat transfer coefficients, pressure gradients, permeability, inertia and drag coefficients; moreover, it also reports two meaningful parameters: the normalized mean wall temperature and the pumping...
Natural convection of air in horizontal parallel plates without and with aluminum foam is experimentally and numerically investigated. The lower wall is heated at uniform heat flux and the upper parallel plate is not thermally insulated to the external ambient. The investigation is carried out by means of a visualization technique and heated wall temperature measurements. The investigated aluminum foam had 10 and 30 Pores per Inches (PPI). The considered configurations are compared and it is found that the presence of the aluminum foam determines a better thermal heat transfer with respect to the clean channel with a low emissivity whereas higher heated wall temperature values with respect to the clean channel with the heated lower plate at high emissivity. Flow visualization is carried out to detect the development and the shape of the main flow and the transitions along the channel. Results of the visualization allow the description of secondary motions inside the channel.
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.
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.
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.