Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
Thermal Efficiency of Open-Cell Metal Foams with Different Thickness: A Comparative Analysis between Correlations and Numerical Modeling
Submission Author:
Leonardo Manetti , MS
Co-Authors:
Leonardo Manetti, Iago Lessa Oliveira, Elaine Maria Cardoso
Presenter: Leonardo Manetti
doi://10.26678/ABCM.COBEM2021.COB2021-0632
Abstract
Direct-immersion cooling with dielectric fluids is a suitable solution for the electronics industry because they allow the components to be immersed without short-circuiting and have a relatively low boiling point (≈ 60-78 °C) keeping the system below the critical temperature. Techniques to modify the heating surface have been proposed to increase boiling performance and a suitable extended surface for the industry is a so-called open-cell metal foam. This work used numerical techniques to calculate the extended surface efficiency and to analyze the impact of the foam’s thickness on its efficiency. Moreover, the numerical results were compared with analytical models. Heat conduction was simulated in an open-cell copper foam with three different thicknesses, 3 mm, 2 mm, and 1 mm, under convection boundary conditions obtained from pool boiling experiments with two dielectric fluids, HFE-7100 and ethanol, at saturation conditions and atmospheric pressure. The geometries of the foams were segmented from μCT images by using the VMTK® library, converted to the stereolithography (STL) format, and used to build the computational meshes. The numerical simulations were carried out in foam-extend-4.0, a library for solving partial differential equations by using the Finite Volume Method for discretization. The numerical extended surface efficiency was compared with classical analytical models (that consider the foam fiber a pin fin with a uniform cross-section) and other correlations from the literature. The foam efficiency increased as the thickness decreased. The thinnest copper foam showed better efficiency than the other ones mainly because the boiling heat transfer coefficient (HTC) is high and the entire foam length is not useful. Moreover, metal foam under pool boiling of ethanol had lower efficiency than HFE-7100 due to the higher HTC of the ethanol. Regarding the comparison between numerical data with analytical models; in general, the errors decreased as the foam thickness decreased, except for the ‘infinite fin’. The pin fin model with adiabatic tip was the one with the lowest mean absolute error, lower than 10% for all cases, being the copper foam with 1 mm and HFE-7100 the case with the lowest error, approximately 1%. On the other hand, the models that consider a three-dimensional matrix presented errors higher than 30%. Thus, for the boiling process, the one-dimensional pin fin model provides efficiencies closer to the numerical simulation results.
Keywords
Thermal Efficiency, metal foam, Numerical analysis, foam thickness, Convective Boiling
