Porous Aluminum Foam Heat Sink, Non-Equilibrium: Paper Validation

Non-Equilibrium Porous Aluminum Foam Heat Sink, Paper Numerical Validation, CFD Simulation by ANSYS Fluent

Description

This project simulates inlet airflow into a vertical cylindrical chamber containing an aluminum fin connected to a heat source, with the domain modeled as a porous material — a non-equilibrium porous aluminum foam heat sink, simulated using ANSYS Fluent. Results are compared and validated against the reference article "Heat transfer characteristics of aluminum-foam heat sinks with a solid aluminum core."

The 2D geometry, modeled axisymmetrically due to its symmetrical structure, was designed in Design Modeler, consisting of three main regions: the incoming open airflow space, the porous aluminum zone, and a solid aluminum fin. The domain was meshed in ANSYS Meshing using a structured grid totaling 87,000 elements.

Methodology

Airflow enters the chamber vertically downward from the upper section and exits horizontally through the side sections at the bottom, assumed to be fully developed given the cylinder's relatively tall geometry. Inlet air enters at 300 K, with velocity varied across the study since the Reynolds number itself is a variable parameter, ranging between 29 and 89 — placing the flow within the laminar regime throughout.

A small cylindrical aluminum fin sits at the bottom of the cylinder, surrounded by a porous aluminum foam medium occupying the space between the inner and outer cylinders. This porous zone was defined with a viscous resistance (inverse permeability) of 58,888,270 1/m², an inertial resistance of 1000.794 1/m, and a porosity coefficient of 0.87 — the ratio of fluid space to total volume — all derived from the reference paper's formulas.

Since the porous zone is not in thermal equilibrium, the non-equilibrium thermal option was enabled, requiring a heat source term defined via the relation Hsf·Asf·(Ts−Tf). Based on the article's formulas, the interfacial area density was set to 2864.27 1/m and the interfacial heat transfer coefficient to 54.78671 W/m²·K. A copper heat source at the chamber's base, which experimentally produces surface temperatures between 320 K and 360 K, was modeled here at a constant surface temperature of 330 K.

Three distinct interface boundaries were defined: between the porous medium and the aluminum fin, between the air and the aluminum fin, and between the porous medium and the open air. In the first two cases, since aluminum solid borders one side, only heat transfer occurs across the interface with no mass transfer; in the third case, both heat and mass transfer occur simultaneously.

Conclusion

This study aims to evaluate the Nusselt number — representing the ratio of convective to conductive heat transfer — within the porous region of the chamber across varying Reynolds numbers. The Nusselt number was calculated at the contact surface between the solid fin and the porous material at the chamber's base, across the full range of tested Reynolds numbers, and compared directly against Figure 3 of the reference article to confirm the simulation's validity and accuracy relative to the published results.