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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.
Switching from an air-cooled system to liquid is not a decision to be made quickly or lightly; there are many factors and possibilities to consider when improving your thermal management to handle higher heat loads. Although market trends indicate that full liquid cooling systems will eventually be the industry standard for cooling power electronics, there are many options and hybrid solutions that can apply the benefits of both as your system evolves or upgrades. If budget or timeline constrictions are such that a direct switch to liquid is unrealistic, optimizing your forced convection solution either through design improvements or by introducing two-phase cooling or liquid components are viable interim solutions.
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.
As you consider the switch to liquid cooling in order to improve the performance of your power electronics devices and
facilities, there are several key determining factors:
• What are your size, weight, and thermal performance requirements?
• Can you further optimize your air cooled system?
• How much longer will air cooled systems be a viable thermal solution for your application?
• Are there any limitations on liquid or volume availability?
• How long will it take for investment in liquid cooling to make a return on performance and efficiency?
• How can liquid cooling be implemented or designed into your application? What will be the effect on application/facility down time?
• How and when do you begin?
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.
Air Cooling Modifications and Hybrid Solutions
There are three common methods of improving your air cooled system. The first is to optimize your heat sink design and
fan selection. Generating more air flow, optimizing your fin geometry, or increasing your heat sink volume are ways to
improve upon your air cooled solution without introducing additional technologies. The second is to introduce two
phase cooling into your design.
Heat pipes may be integrated to spread higher power densities or move the heat to an
area where it can be more easily dissipated. The third most common method of increasing the performance of an air
cooled solution is to start introducing elements of a liquid system such as a
passive thermosiphon.
View The Air Cooling Product Page
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.
Liquid Cooling Solutions
The AAVID Hydrosink™
The Aavid HydroSink™ system is a configurable method of combining a
standard set of optimized heat exchangers, fans, pumps, valves, reservoirs,
fittings, sensors, and control boards with custom cold plates to design the
best possible liquid cooling solution for given requirements.
HydroSinks™ offer more flexibility in design and installation than standard
liquid cooling systems because they are configurable and more easily
adapted to design requirements. Sealing and connecting of the liquid cold
plate, control board, and customer machine controls within the enclosure
are also customizable.
As Aavid HydroSinks™ are largely comprised of a set of standard optimized
components, they are more cost effective than traditional custom liquid
cooling and their air cooled counterparts.
Currently the Aavid HydroSink™ is available in two basic compact system sizes, Small and Medium. Actual size of the
final customer HydroSink™ system varies by configuration. Sizes are based around fan size and cooling performance.
Small operates at a temperature rise 7-20 °C per kW, while the Medium operates at a rise of 3-9°C per kW.
Click for more information about the Aavid HydroSink™ System.
AAVID Liquid Cold Plates
Customized Aavid Liquid Cold Plates are an integral part of the HydroSink™ system. Aavid offers four distinct, innovative
cold plate designs developed to optimize the overall system based on application and requirements. All Aavid cold plates
are constructed for worry-free liquid cooling utilizing specialized certification procedures to ensure leak-free, reliable
solutions.
Hi-Contact™ Tube Cold Plates
Aavid Hi-Contact™ tube liquid cold plates feature a high performance
assembly utilizing a continuous tube press fit into an extruded aluminum
plate. The patented geometry used in the Aavid Hi-Contact™ process moves
the fluid closer to the device generating heat, achieving the best thermal
performance from a tube cold plate. To further increase the performance of
Aavid's Hi-Contact™ liquid cold plates, a thermal epoxy is applied to the joint
to provide a gap free thermal interface between the tube and the plate. Hi-Contact™
plates are easy to customize and are available in standard sizes.
Blister Cold Plates
Blister technology stamps channels into the base plate, eliminating channel
machining and greatly lowering manufacturing costs. A leak free joint is created
between the base and cover plate and the blister channels to allow greater
flexibility to drill mounting holes in the topside of the cold plate without regard
for the location of the liquid channels.
Vortex Liquid Cold Plates
Aavid Vortex Liquid Cold Plates are designed to cool extremely high power
applications. These cold plates were initially developed for applications where a
high compressive load may be applied such as when cooling SCR type devices.
Using patented flow path geometry, both sides of Vortex Liquid Cold Plates are
evenly cooled; therefore they can provide equal and consistent performance
across both surfaces and lend themselves to creating more predictable
environments.
Extended Surface Liquid Cold Plates
Aavid Extended Surface Liquid Cold Plates have increased internal surface area
which allows for better overall heat transfer. Innovative technologies and
manufacturing processes are used to increase the liquid to plate contact area
within the liquid cold plate. Their vacuum brazed construction ensures leak free
joints while maintaining high thermal conductivity. Aavid Extended Surface
Liquid Cold Plates are specially fabricated to improve design flexibility and can
be easily customized for optimized flow paths for application designs.
View The Liquid Cooling Product Page
Final Thoughts
The key to effective design for liquid cooling and optimized air cooled systems is to consider your thermal management
as early in the design phase as possible. Aavid offers design, engineering, and testing services that can come in at any
phase and develop the best possible solution based on requirements, constraints, timeline, budget, and any other
critical factors.
With design centers around the world, Aavid can provide any customer the necessary engineering services to design and
manufacture a fully optimized system. Engineers are available at every phase from analyzing if there is a need for liquid
cooling or air cooling, to developing an optimized, integrated system, to reliability and validation testing of the entire
device.
To request a free consultation about your current cooling solutions or for help finding the right thermal
solution for your Power Electronic Applications click here.
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