Forced Convection in High Porosity Metal Foams

This paper reports an experimental and numerical study of forced convection in high porosity (ε∼0.89–0.97) metal foams. Experiments have been conducted with aluminum metal foams in a variety of porosities and pore densities using air as the fluid medium. Nusselt number data has been obtained as a function of the pore Reynolds number. In the numerical study, a semi-empirical volume-averaged form of the governing equations is used. The velocity profile is obtained by adapting an exact solution to the momentum equation. The energy transport is modeled without invoking the assumption of local thermal equilibrium. Models for the thermal dispersion conductivity, kd, and the interstitial heat transfer coefficient, hsf, are postulated based on physical arguments. The empirical constants in these models are determined by matching the numerical results with the experimental data obtained in this study as well as those in the open literature. Excellent agreement is achieved in the entire range of the parameters studied, indicating that the proposed treatment is sufficient to model forced convection in metal foams for most practical applications. [S0022-1481(00)01903-4]</jats:p

The effective thermal conductivity of high porosity fibrous metal forms

Greek Symbols e = Porosity Introduction Starting with the pioneering work of Maxwell (1891), heat conduction in fully saturated porous matrices (e.g., sand, packed beds of cylinders and spheres, fibrous insulations, etc.) has been studied in detail over the past several decades. Under simplified one-dimensional conduction conditions, two extremes can be considered. One in which the thermal resistances offered by the solid and fluid phases are in series (lower bound) and the other in which they are in parallel (upper bound). The upper bound, given by Eq. (1)

Numerical Analysis of a Paraffin/Metal Foam Composite for Thermal Storage

In the last decade, the use of Phase Change Materials (PCMs) as passive thermal energy storage has been widely studied both analytically and experimentally. Among the PCMs, paraffins show many advantages, such as having a high latent heat, a low vapour pressure, being chemically inert, stable and non-toxic. But, their thermal conductivity is very low with a high volume change during the melting process. An efficient way to increase their poor thermal conductivity is to couple them with open cells metallic foams. This paper deals with a theoretical analysis of paraffin melting process inside an aluminum foam. A mathematical model is developed by using the volume-averaged governing equations for the porous domain, made up by the PCM embedded into the metal foam. Non-Darcian and buoyancy effects are considered in the momentum equation, while the energy equations are modelled with the Local Thermal Non-Equilibrium (LTNE) approach. The PCM liquefaction is treated with the apparent heat capacity method and the governing equations are solved with a finite-element scheme by COMSOL Multiphysics. A new method to calculate the coupling coefficients needed for the thermal model has been developed and the results obtained have been validated comparing them to experimental data in literature