What Is a Heat Sink and How Does It Work? Answers Are Here

What Is a Heat Sink?

First of all, what is a heat sink? It can be also spelled heatsink, which is a passive heat exchanger that can transfer the heat generated by electronic or mechanical equipment to a fluid medium (usually air or liquid coolant), and then dissipate from the equipment to regulate the temperature of the equipment.

In computers, heat sinks are used to cool CPUs, GPUs, certain chipsets, and RAM modules. The heat sink is used in high-power semiconductor devices (like power transistors) and optoelectronic devices (like lasers and LEDs), where the heat dissipation capacity of the component itself is insufficient to regulate its temperature.

The design of the heat sink maximizes the surface area in contact with the surrounding cooling medium (such as air). Air velocity, material selection, protrusion design, and surface treatment are factors that affect the performance of the heat sink.

The attachment method of the heat sink and the thermal interface material also affect the die temperature of the integrated circuit. Thermal adhesive or thermal grease can improve the performance of the heat sink by filling the air gap between the heat sink and the heat spreader on the device. The heat sink is usually made of aluminum or copper.

The heat sink transfers heat energy from the high-temperature equipment to the low-temperature fluid medium. The fluid medium is usually air, but it can also be water, refrigerant, or oil. If the fluid medium is water, the heat sink is usually called a cold plate. In thermodynamics, a heat sink is a heat storage device that can absorb any heat without significantly changing the temperature.

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How Does It Work?

After you get some information about the heat sink, you may want to know how does it work. Actually, almost all heat sinks work in four basic steps:

1. The source generates heat. The heat source may be any system that generates heat and needs to remove the heat to make it function properly, for example: mechanical, electrical, chemical, and so on.
2. Heat is transferred from the heat source. In applications that directly contact the heat sink, heat enters the heat sink through natural conduction and is removed from the heat source. The thermal conductivity of the heat sink material directly affects this process. This is why the most common materials in the construction of heat sinks are materials with high thermal conductivity, such as copper and aluminum.
3. The heat is spread throughout the heat sink. The heat will naturally pass through the heat sink through natural conduction which moves through a thermal gradient from a high temperature to a low-temperature environment. This ultimately means that the heat distribution of the heat sink will be inconsistent. In this way, the heat sink usually heats up towards the source and cools towards the end of the heat sink.
4. Heat is removed from the heat sink. This process depends on the temperature gradient and the working fluid of the heat sink. This stage also relies on temperature gradients to remove heat from the heat sink. Thus, if the ambient temperature is not cooler than the heat sink, convection and subsequent heat dissipation will not occur. Besides, the large surface area provides an increased area for thermal diffusion and convection to appear.

Active Heat Sinks VS Passive Heat Sinks

Passive heat sinks depend on natural convection, which means that only the buoyancy of the hot air will cause the airflow generated across the heat sink system. These systems are advantageous because they do not need a secondary power supply or control system to dissipate heat from the system. Nevertheless, passive heat sinks are not as efficient at transferring heat from the system as active heat sinks.

Active heat sinks use forced air to increase fluid flow through high-temperature areas. Forced air is usually generated by the movement of a fan, blower, or even the entire object. An example of a fan that generates forced air on a heat sink is when the computer gets hot and the fan in the personal computer turns on.

The fan forces air through the heat sink, which causes more unheated air to move across the heat sink surface, thereby increasing the overall thermal gradient of the entire heat sink system and allowing more heat to escape from the entire system.