Understanding Heat Sinks: Functions, Types, & More

[Andy L. Goff]

A heat sink is one of the most common forms of thermal management in technology, machinery, and natural systems. Unfortunately, it is easy to overlook these components, even for those familiar with the technology. During this session, we will cover basic working principles, introduce active and passive heat sink configurations, and discuss how some users implement heat sinks in their applications.

What is a Heat Sink?

The purpose of a heat sink is to increase the flow of heat away from a hot device. Due to this increase in working surface area and flow rate, the device can operate at lower temperatures. Heat sinks differ based on each device's configuration in terms of aesthetics, design, and ultimate capabilities. For example, the image at the top of this article shows a straight fin heat sink, while the photo below shows a flared fin heat sink. There are a variety of applications that can benefit from each heat sink:

How Does a Heat Sink Work?

Heat sinks work by removing heat from critical components. A heat sink accomplishes this task in four basic steps:

1. The source generates heat. The source may be any system that creates heat and needs to remove to function correctly, such as:

- Mechanical

- Electrical

- Chemical

- Nuclear

- Solar

- Friction

2. Heat transfers away from the source. Heat pipes can also assist this process, but we'll discuss them separately. Natural conduction moves heat from the source to the heat sink in direct contact applications. The thermal conductivity of the heat sink material directly influences this process. Copper and aluminum are the most common materials used to construct heat sinks.

3. Heat distributes throughout the heat sink. Heat moves from a high to a low-temperature environment via natural conduction and naturally travels through the heat sink. The result is a heat sink with a non-consistent thermal profile. Therefore, heat sinks tend to be hotter at their sources and more excellent at their extremities.

4. Heat moves away from the heat sink. This process relies on the heat sink's temperature gradient and working fluid, usually air or a non-electrically-conductive liquid. Thermal diffusion and convection remove heat from the surface of the warm heat sink by passing the working fluidly across it. Again, this stage relies on a temperature gradient to remove heat from the heat sink. Convection can only occur if the ambient temperature is more excellent than the heat sink. The heat sink's total surface area becomes most advantageous in this step. The surface area provides a more important place for thermal diffusion and convection.

Active Heat Sinks vs. Passive Heat Sinks

There are three heat sinks: active, passive, and hybrid.

Passive heat sinks generate airflow solely through buoyancy. Due to the lack of secondary power or control systems, these systems are advantageous. A passive heat sink, however, is less efficient at transferring heat than an active heat sink.

Active heat sinks are cooled by forced air. Moving the entire object or using fans or blowers can cause a perspective. Motorcycles, for example, cool their engines with air passing along their heat sinks. Your computer's fan turns on after warming to force air across a heat sink. A fan forces air across the heat sink, allowing more unheated air to move across the surface, thus increasing the thermal gradient across the heat sink system and allowing more heat to exit.

Hybrid heat sinks combine aspects of passive and active heat sinks. Temperature control systems are often used in these configurations to cool the system based on requirements. The forced air source is inactive during cooler temperatures, cooling the system passively. As the source temperature increases, the active cooling mechanism increases the heat sink's cooling capacity.