Leveraging computational fluid dynamics in heat sink designs

In the realm of electronics design, heat sinks are essential devices that help to dissipate heat produced by electronic or mechanical devices. These thermal management devices play a pivotal role in the performance and longevity of electronic devices by preventing overheating.

Designing an effective heat sink, however, presents its own set of challenges. There are several variables at play, such as the shape and material of the heat sink and the airflow conditions, among other things. Finding the optimal combination of these variables to improve the heat sink’s performance is easier said than done. For instance, creating and testing new heat sink prototypes can be time-consuming and resource intensive.

Source: Soumen/Adobe Stock

Computational fluid dynamics (CFD) tools have become especially relevant in designing heat sinks, primarily because of their ability to model complex fluid and heat transfer scenarios, which are integral to effective heat sink design.

CFD: A quick primer

CFD is a branch of fluid mechanics that uses numerical methods and algorithms to solve, analyze and simulate engineering problems involving fluid flow and heat transfer. CFD tools rely on a set of fundamental differential equations called the Navier-Stokes equations, which are based on the principles of conservation of momentum and conservation of mass. These equations are combined with the conservation of energy equations to provide a complete mathematical model and description of fluid flow.

The equations are:

1. Conservation of mass (or the continuity equation)

2. The conservation of momentum

3. Conservation of energy

Where is the fluid density, u is the velocity vector, is the pressure, is the dynamic viscosity, g is the acceleration due to gravity, cp is the specific heat at constant pressure, T is the temperature, k is the thermal conductivity and S is the volumetric heat source.

Learn more: Introduction to computational fluid dynamics

CFD in heat sink design

By applying CFD to heat sink design, engineers can gain valuable insights into air velocity, temperature distributions, pressure drops and heat transfer coefficients. In addition, CFD provides valuable information about thermal resistance and pressure drop, all of which are valuable for optimizing heat sink performance.

Figure 2: CFD provides valuable information about thermal resistance and pressure drop, all of which are valuable for optimizing heat sink performance. Source: Isofilm/CC[SA][3.0]

The thermal resistance provides a measure of the resistance to heat flow through the heat sink and indicates how effectively the heat sink transfers thermal energy from the heat-generating component to the surrounding medium (such as air or liquid coolant). Results from CFD simulations provide information about the temperature difference between the heat sink and the ambient. And the thermal resistance can be calculated using:

Where:

R is the thermal resistance (measured in °C/W)

is the difference between the heat sink and ambient temperatures (°C)

Q = heat input to the heat sink (W)

A lower thermal resistance means a more efficient heat sink, as it indicates that the heat sink causes a smaller temperature increase for each unit of power it must dissipate.

However, with an increase in heat transfer performance caused by convective heat transfer and heat sink fins, there is always an accompanying effect of pressure drop. Engineers try to strike a balance between enhancing heat transfer and minimizing pressure drop in heat sinks, as higher pressure drop translates to more energy demand or pumping power requirement.

[Learn more about heat sink design on GlobalSpec]

Enhancing heat sink designs with CFD

Traditional heat sink design often involves educated guesswork, followed by prototyping and testing. With CFD, engineers can simulate various heat sink designs (using different materials, working fluids, fin spacing, fin thickness, and flow velocities), effectively reducing the need for physical prototypes, saving time, and cutting costs.

However, while CFD provides many benefits, its results can only be as accurate as the input parameters and boundary. Moreover, it is essential to have a deep level of understanding of the fundamental topics that guide the operation of CFD tools, such as fluid mechanics, heat transfer, numerical methods and turbulence.

Learn more about the different computational fluid dynamics (CFD) suppliers.