Validation of a Heat sink using ANSYS Icepak

Introduction:

Heat sink is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, thereby allowing regulation of the device's temperature. In computers, heat sinks are used to cool CPUs, GPUs and some chipsets and RAM modules. A heat sink is designed to maximize its surface area in contact with the cooling medium surrounding it, such as the air. Heat sink attachment methods and thermal interface materials also affect the die temperature of the integrated circuit. To improve the performance of the heat sink, thermal adhesive or thermal grease are used to fill air gaps between the heat sink and the heat spreader on the device. A heat sink is usually made out of high thermal conducting materials like aluminium, copper, etc.

Figure: Fan cooled heat sink

Parameters affecting performance of a heat sink:

1. Air velocity

2. Choice of material

3. Protrusion design

4. Surface treatment

Objective of the project:

In this Project, a heat sink has to modelled as per the specifications provided and validated. According to the design objective, the base of the devices should not exceed 65°C when air sweeps the fins at an ambient temperature of 20°C. A Reference image of the model has been provided below.

1. Geometry modelling:

1. Initially, the Cabinet has been created and the size of the cabinet is 75 mm X 250 mm X 356 mm

2. Then, the Backing plate of 6mm thickness is attached and five sources are placed on the backing plate. Source-1 is located at {0mm, 31.5 mm, 180.5 mm} having power dissipation 33W eah placed at a 45mm distant apart. Also, a Opening has been provided at the Max-z side of the cabinet to allow the air outflow.

3. Then, 10 Aluminium extruded fins of thickness 2.5 mm having width 69 mm in X dir and length 281 mm in Z dir and all fins are 25 mm apart.

4. The Final step is to place 3 fans asper the dimensions. Here, Fan-1's center is at Z min (40mm, 47.5 mm, 0mm) having an external radius of 30 mm and an internal radius of 10 mm. the fan has fixed volumetric flow 18 CFM. Other two fans has to be placed 77.5 mm apart from each other.

2. Meshing the model:

A Coarse mesh has been developed for study in this case. The Mesh settings used are displayed below:

This is the final coarse meshed model obtained with 67,805 mesh elements and also, a cut plane is inserted at the center of the model, describing the mesh distribution.

3. Setting up the case:

3.1. Fan:

All three fan objects are set as intake fans with a fixed volumetric flow rate of 18 cfm.

Temperature and pressure are set to ambient conditions. (Ambient temperature is set to 20 deg)

3.2. Source:

All five heat sources are set to a constant power of 33W.

3.3. Problem setup:

The Case has been set to solve for velocity, temperature and pressure with zero equation model ignoring the radiation through problem setup option.

The Solution settings used are displayed below:

3.3.1. Basic settings:

3.3.2 Discretisation schemes:

3.3.3 Under-relaxing parameters:

4. Solution description:

The Case has been ran and the solution has converged nearly at 100 iterations. The Residual plot has been attached below.

4.1. Maximum temperature data:

As per the report data, the maximum temperatures of all objects are provided below and it can be seen that all the objects are below 60 deg as required.

source.1.1 - 54.8835 C
source.2 - 52.9898 C
source.3 - 52.6788 C
source.4 - 53.1707 C
source.5 - 55.4403 C

block.1 - 51.7758 C
block.1.1 - 50.6409 C
block.1.2 - 49.5031 C
block.1.3 - 49.9067 C
block.1.4 - 49.0089 C
block.1.5 - 49.5458 C
block.1.6 - 49.6517 C
block.1.7 - 50.1142 C
block.1.8 - 50.3732 C
block.1.9 - 52.1506 C

4.2. Temperature contour:

The temperature contour has been created at different cut-planes to observe the distribution. From this figure, we can observe high temperature near the source. Also, on the plane near the fans shows that the temperature distribution is majorly dominated by the conduction as its convected by a ambient air supply of 20 degC. When we look into the farthest plane, the air near the plate fins is having a temperature hike of nearly 8 degC.

4.3. Velocity contour:

A Velocity contour has been introduced at a cut-plane with vectors to study the velocity distribution over the domain. It can be seen that the Max. velocity is 3.39 m/s and also, the boundary layers formed near the walls of the cabinet and the planes can be clearly seen.

5. Conclusion:

1. The Maximum temperature on the domain is 55.44 degC, which is below our temperature objective (65 degC).

2. The Accuracy of the solution can be improved with a finer mesh.

3. The temperature can even be controlled by using more number of fins with a lesser thickness increasing effectiveness of the heat dissipation.