Non-Equilibrium Porous Aluminum Foam Heat Sink, Paper Validation

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

This project simulates the inlet airflow to a vertical cylindrical chamber with an aluminum fin connected to a heat source (heat sink). The domain is made of porous material. Non-Equilibrium Porous Aluminum Foam Heat Sink is modeled by ANSYS Fluent.

The results of this simulation are compared and validated with the article “Heat transfer characteristics of aluminum-foam heat sinks with a solid aluminum core.” We design the geometry of the present model using Design Modeler software.

The present model is two-dimensional, and we model it axisymmetric due to its symmetrical structure. This model consists of three main parts: the space for the incoming open airflow, the space related to the porous aluminum zone, and the space for a solid aluminum fin.

We carry out the meshing of the model using ANSYS Meshing software. The mesh type is Structured, and the element number equals 87000.

Methodology

The airflow enters the chamber vertically and downwards from the upper section and exits horizontally from the side sections at the bottom of the chamber. Inlet airflow is assumed to be a developed flow; Hence, the height of the cylinder is assumed to be relatively high.

The inlet airflow has a temperature of 300 K and has variable velocities since the Reynolds number of the model will be variable.

The Reynolds studied in the present numerical work varies between 29 and 89, and therefore it can be said that the model has a laminar flow. At the bottom of the cylinder is a small cylindrical fin that acts as a solid body of aluminum.

A porous environment made of aluminum foam is located in the space between the two outer and inner cylinders. The viscous resistance in a porous medium is the inverse of the fluid permeability in the porous medium, which is equal to 58888270 1/m2 according to the formula in the paper.

According to the article’s formula, the inertial resistance value is 1000.794 1/m. The porosity coefficient in a porous medium is equal to the ratio of fluid space to the total environment space, which in the present problem is equal to 0.87.

The porous zone of the problem is not an equilibrium in terms of temperature; Therefore, the non-Equilibrium option must be enabled. When using non-Equilibrium thermal equations, a term related to the heat source is obtained, which according to the relation Hsf.Asf (Ts-Tf), it is necessary to define the values ​​of Hsf and Asf.

Therefore, according to the article’s formulas, the interface zone density value is assumed to be 2864.27 1.m-1, and the value of the heat transfer coefficient is assumed to be 54.78671 W/m2.K.

At the bottom of the chamber, a copper heat source is used, which creates a temperature in the range of 320 K to 360 K at the surface of the copper heat source. In this numerical work, it is assumed that the surface of this heat source has a constant temperature of 330 K.

This problem is characterized by the use of interface surfaces in three areas. The boundary between the porous medium and the aluminum fin, the boundary between the air and the aluminum fin, and the boundary between the porous medium and the open air.

In the first two cases, since we use an aluminum solid on one side of the boundary, only heat transfers from the boundary, and there is no mass transfer; In the third case, in addition to heat transfer, mass transfer also occurs.

Conclusion

This problem aims to investigate the value of the Nusselt number (equivalent to the convection-conductivity ratio) in the porous region of the chamber in different Reynolds numbers.

At the end of the solution process, we obtain the value of the Nusselt number at the contact surface between the solid fin and the porous material at the bottom of the chamber in terms of different values of the Reynolds number for the incoming airflow.

We validate and compare the results with Figure 3 of the article.