‍Let me start by explaining natural convection. Natural convection is the process by which heat is transferred through a fluid (such as air) without the aid of fans or pumps. This occurs when a fluid in contact with a hot surface gets heated, becomes less dense, and rises, allowing cooler fluid to take its place. This cycle creates a natural flow that exchanges heat effectively.

This principle has been widely used for many years as heating for homes in Europe where radiators create convection currents, where the warm air rises above the radiator and simultaneously draws in more cold air from below, circulating heat throughout a room, arguably much more efficiently than the forced convection we see in North American homes.

Source: Best Heating

🔑The key...

to this working effectively is to uniformly heat the surface by pumping hot water through the radiator - if the system gets clogged and hot spots are created then the effectiveness is quickly reduced.

In the context of cooling, natural convection leverages this simple principle of heat rising and engineers design systems that optimize this natural flow. This allows engineers the ability to create efficient cooling solutions without the need for mechanical assistance (pumps or fans).

There are many examples of passive heat sinks combining conduction and convection into air to manage low power electrical devices - the problem today is that power density is too high and natural convection heat sinks are unable to effectively cool a component as the heat cannot be spread uniformly over the fins.

How to Make Natural Convection Feasible for High Performance Cooling

To make natural convection feasible for high-performance cooling, several factors must be considered:

1. Design Optimization: The shape and orientation of components can significantly impact the efficiency of natural convection. Vertical arrangements and open structures (the opposite of tightly packed fins) allow for better airflow and this creates a chimney effect.
2. Material Selection: Using materials with high thermal conductivity enhances heat transfer, making natural convection more effective - but this must always be balanced with cost.
3. Environmental Considerations: Ensuring that the cooling system is exposed to ambient conditions that facilitate natural convection. An open, well ventilated environment is crucial.

🔑The key to the future...

Is integration with other types of passive cooling. By combining natural convection with other passive cooling technologies high performance cooling solutions become feasible. These technologies could inside:

• Heat Pipes
• Vapor Chambers
• Pulsating Heat Pipes
• Loop Heat Pipes

These technologies all provide the ability to transport heat to the convection zone more efficiently, providing a much larger surface to dissipate the heat into the air.

3 Examples of what can be achieved with Natural Convection

Source: Calyos

1: Rail Traction Inverter

This loop heat pipe solution was able to passively cool a peak load of 11.2kWs of thermal power, produced by an array of 8 IGBTs. The condenser used widely spaced fins (7mm distance) to maximize the chimney effect and provide the ability to dissipate the heat. This design also minimized thermal swings, enhancing component longevity. A highlight was that through better cooling (vaporization) of the high-power components, they were each able to run more efficiently. In turn this reduced the number of IGBTs for the system from 12 to 8, representing a significant cost saving for our customer. The system was also completely silent, in contrast to the loud fans we are familiar hearing on trains, this was a welcome feature for end users.

Source: Nextpit

2: Galaxy S Mobile Phones

‍It's easy to forget without an array of fins that cell phones with their smooth back plates are using this as the primary surface for natural convection into the air. Yes the power is much lower. No they are not creating a chimney effect. But without an ever increasing vapor chamber inside the processor would thermally throttle and produce a noticeable hotspot on the back of every phone. Instead we are able to benefit from higher and higher mobile performance primarily thanks to these highly effective vapor chambers. The size increase of smartphones over the last decade has also allowed for higher power processors as the size of the vapor chambers can increase as you can see in the image above.

Source: Streacom

3: Streacom PC Case

‍The Streacom SG10 is a high-performance, fanless gaming PC case that utilizes loop heat pipe technology in tandem with natural convection, allowing it to dissipate up to 600W of heat without the need for fans. The case's design features a unique structure made from precision-milled aluminum and steel (and a special edition copper version), offering excellent cooling efficiency for the latest high-performance CPUs and GPUs like the Intel Core i9-13900K or AMD Ryzen 9 7950X3D, and powerful GPUs such as the NVIDIA RTX 4070.

A Reminder of the KeyTo make Natural convection, when paired with passive cooling technologies, offers a powerful solution for high-performance, zero-maintenance cooling. Its simplicity and reliability make it an attractive option for a wide range of applications. Explore the potential of natural convection in your systems and experience the benefits of efficient, sustainable cooling.