Over the past few decades, Power & Energy have emerged as two of the fastest growing industries in electronics. Power conversion, inversion, and rectification as well as battery and fuel cell technologies have become integral to technological growth across all industries.

　　As power electronic systems become more complex and perform at higher power ranges, the form factors are getting smaller, making heat one of the greatest limiting factors to what can be accomplished. To handle the amount of power being dissipated, air cooling solutions must be optimized and enlarged to adequately remove the excess heat. In some cases, size becomes a limiting factor for forced convection solutions. In these cases where the size or weight of an air cooled system makes it impractical, liquid cooling is fast becoming the most popular alternative method.

　　Engineers have been developing liquid systems that are complimentary to existing air cooled solutions that can be expanded to fully replace the air cooled systems over time. This is done by focusing on the electronic devices that can gain immediate benefit with liquid cooling. Utilizing fluid couplings, reliable pump systems, and compact heat exchangers, the system removes heat from the air flow to the liquid where it is transferred and managed elsewhere. In other cases,engineers are opting to fully replace their air cooled systems with liquid cooled to immediately enable higher power outputs and optimize thermal performance.

　　Air Cooling Benefits

　　Air cooled systems are significantly less expensive than liquid systems. They do not require regulated or specialized fluids and they are comprised of fewer components that are more economical than components for liquid systems. As they have no liquids to leak and less components to break, they also have less modes of failure. In addition to having higher reliability and lower cost, air cooled systems are also easier to modify or upgrade.

　　Air Cooling Limitations

　　In typical applications, air cooling systems are comprised of an extruded or bonded fin heat sink and often a fan. When reliability is a significant factor, engineers may forgo a fan and instead opt for passive solutions.

　　Both natural and forced convection have limitations. Natural convection is limited by the total surface area needed to dissipate heat, this necessitates large, heavy solutions that are often impractical.

　　Forced Convection solutions are limited by pressure drop. Heat sinks with large surface areas in feasible volumes create a high amount of air resistance that hinder the amount of flow and therefore heat transfer that a fan can produce. Larger forced convection solutions also require larger or more fans, increasing the amount of noise generated by the solution.

　　However, the biggest limitation of air cooled solutions is thermal performance. Air does not have the same capacity as liquid to absorb and transfer heat. At a certain threshold, air cooling becomes an insufficient solution and liquid cooling is necessary.

　　The Efficacy of Liquid Cooling

　　Liquid has the capacity to transfer heat up to 4X higher than the capacity of air of the same mass. This enables higher thermal performance in a smaller solution. A liquid cooling system is a hydraulic circuit that typically consists of a cold plate that interfaces with the heat source and device, a pump that circulates the fluid through the system, and a heat exchanger that rejects the heat absorbed by the liquid from the device. Liquid cold plates have a much smaller working envelope than a heat sink that would be used in air cooling for the same application. Additionally, multiple cold plates can be connected to the same exchanger with minimal impact on performance. Liquid cooling grants an additional level of control over the cooling system because it controls inlet temperature to the cold plate as well as flow rate.

　　Potential Risks & Trade Offs of Liquid Cooling

　　Some have been reticent to adopt liquid cooling because of the additional complexity and the fear of leakage.Complexity often increases the cost of the solution and the amount of maintenance required to keep the system running. However the additional costs are mitigated in that the improved cooling performance will increase the lifetime and reliability of your device.

　　Because of its complexity, liquid cooling requires better planning and design to incorporate into your power electronics.Although the cold plate is much smaller than an extrusion or heat sink, the overall solutions tends to occupy more volume once the heat exchangers, tubes, reservoir, and pumps are all taken into account. Engineers must take all of this into account during the initial design phase in order to avoid complications later on. With proper foresight, the complexity of the systems can be beneficial as there is more flexibility in system design.