Category Archives: Liquid Cooling

Nanoparticles to Enhance the Thermal Management of Electronics

The addition of nanoparticles to a coolant are an alternative approach that can be considered to improve the performance of a liquid cooled system or perhaps to further reduce the size of such a system. But nanoparticles are not necessarily well known by engineers engaged in thermal management. This list of material may help.

The addition of nanoparticles to a coolant are an alternative approach that can be considered to improve the performance of a liquid cooled system or perhaps to further reduce the size of such a system.  But nanoparticles are not necessarily well known by engineers engaged in thermal management. This list of material may help.

First, a new paper by Moita, Moreira and Pereira, does an excellent job of reviewing nanofluids for the next generation of thermal management. This paper contributes to the body of knowledge in this space by looking at typical nanoparticle/base fluid mixtures used and combined in technical and functional solutions. It covers the science of nanofluids and their practical application. You can download this open-access paper from the Multidisciplinary Digital Publishing Institute, at this link (download is a PDF): Nanofluids for the Next Generation Thermal Management of Electronics: A Review

Second, ATS was fortunate enough to have had on our research staff, Dr. Reza Azizian. He and others authored a white paper titled “Nanofluids in Electronics Cooling Applications”. This piece discusses the theory and use of nanofluids for thermal management. We’ve posted that paper on the ATS blog here: Nanofluids in Electronics Cooling Applications.

We hope you find these resources helpful. Like always, if you have trouble accessing them, drop us a comment and we’ll get you a copy.

Nanoparticles Shapes & Forms Image used by permission from the artist normaals

How Chillers Are Used in the Liquid Loop and How to Choose the Right Fluid

Chillers can be a key component in the liquid loop. They serve the function of conditioning the coolant before it heads back into the cold plate in a liquid loop. The standard refrigeration cycle of recirculating chillers is displayed below in Fig. 1.

Heat Exchanger
An example of a standard liquid cooling loop using a heat exchanger to transfer heat from the liquid to the ambient. (Advanced Thermal Solutions, Inc.)

The choice of the chiller and the fluid are an important part of the creation of the liquid loop. ATS has some resources to help engineers in this work.

First, engineers can get some help identifying the right fluid to use in their liquid loop with our article “Engineering How-To: Choosing the Right Fluid to Use with Cold Plates“. While water is the most common fluid, our article helps engineers with a specification grid on which fluid to use given different applications.

Another helpful resource for engineers is our article, “Cold Plates and Recirculating Chillers for Liquid Cooling Systems“. This article helps engineers understand the use of both cold plates and chillers deployed in the liquid loop. We also include a comparison of ATS and other industry chillers for quick reference for engineers.

But what if your new to how the liquid cooling loop works? Our 2 min. video walks engineers through. The video “What is a Cold Plate and How Does it Work” is a 2 minute video on the ATS YouTube Channel showing how the liquid loop works.

The Liquid Cooling Loop for thermal management of electronics
The liquid cooling loop and some key features of

Finally, ATS has a line or recirculating, immersion and TEC based chillers that engineers can deploy in their liquid loop to efficiently cool high power electronics. You can learn about them on our web sit here: “ATS Family of
recirculating, immersion and TEC based chillers
“.

ATS Family of Recirculating, TEC Based and Immersion Chillers
ATS Family of Recirculating, TEC Based and Immersion Chillers

How to Calculate the Loads for a Liquid Cooling System

This article presents basic equations for liquid cooling and provides numerical  examples on how to calculate the loads in a typical liquid cooling system. When exploring the use of liquid cooling for thermal management, calculations are needed to predict its performance. While it is often assumed that a liquid coolant itself dissipates heat from a component to the ambient, this is not the case. A closed loop liquid cooling system requires a liquid-to-air heat exchanger. Because of its structure, several equations must be calculated to fully understand the performance and behavior of a liquid cooled system.

Cold plates bring localized cooling by transferring heat to a liquid that dissipates into the ambient or a secondary liquid. ATS cold plates cool high-powered electronics, IGBT modules, lasers, motor devices, automotive components, medical equipment, and other applications where liquid cooling is needed. Their internal, mini-channel fin structure enhances the surface area to maximize heat transfer with low pressure drop characteristics and provides uniform surface temperature.

==> Learn more at our website: https://www.qats.com/Products/Liquid-Cooling/Cold-Plates

White Paper: Microchannel Heat Sink Application in IGBT Modules

Traditionally the IGBT modules were cooled by forced air-cooled heat sinks. Air-cooled heat sinks are still good thermal management solutions for low-power and less temperature-restricting IGBT modules. However, the high-power IGBT modules are exclusively cooled by liquid-cooled heat sinks, also known as cold plates. Learn more about their application in this white paper (PDF, download, no registration needed): Download it here

Engineering White Paper: White Paper: Microchannel Heat Sink Application in IGBT Modules
A microchannel heat sink (also known as a cold plate) can be used to cool high power IGBT

Engineering How-To: Choosing the Right Fluid to Use with Cold Plates

By Norman Quesnel, Senior Member of Marketing Staff
Advanced Thermal Solutions, Inc. (ATS)

Liquid cooling systems transfer heat up to four times better than an equal mass of air. This allows higher performance cooling to be provided with a smaller system. A liquid cooled cold plate can replace spaceconsuming heat sinks and fans and, while a liquid cold plate requires a pump, heat exchanger, tubing and plates, there are more placement choices for cold plates because they can be outside the airflow. [1]

One-time concerns over costs and leaking cold plates have greatly subsided with improved manufacturing capabilities. Today’s question isn’t “Should we use liquid cooling?” The question is “What kind of liquid should we use to help optimize performance?”

Figure 1. A Liquid Cooling System for a Desktop PC with Two Cold Plates. [2]

For liquid cold plates, the choice of working fluid is as important as choosing the hardware pieces. The wrong liquid can lead to poor heat transfer, clogging, and even system failure. A proper heat transfer fluid should provide compatibility with system’s metals, high thermal conductivity and specific heat, low viscosity, low freezing point, high flash point, low corrosivity, low toxicity, and thermal stability. [3]


Today, despite many refinements in liquid cold plate designs, coolant options have stayed relatively limited. In many cases, regular water will do, but water-with-additives and other types of fluids are available and more appropriate for certain applications. Here is a look at these coolant choices and where they are best suited.

Basic Cooling Choices

While water provides superior cooling performance in a cold plate, it is not always practical to use because of its low freezing temperature. Additives such as glycol are often needed to change a coolant’s characteristics to better suit a cold plate’s operating environment.

In fact, temperature range requirements are the main consideration for a cold plate fluid. Some fluids freeze at lower temperatures than water, but have lower heat transfer capability. The selected fluid also must be compatible with the cold plate’s internal metals to limit any potential for corrosion.

Table 1 below shows how the most common cold plate fluids match up to the metals in different cold plate designs.

Table 1: Compatibility Match-ups of Common Cold Plate Metals and Cooling Fluids [1]

The choices of cold plate coolants will obviously have varied properties. Some of the differences between fluids are less relevant to optimizing cold plate performance, but many properties should be compared. Tables 2 and 3 show the properties of some common coolants.

Tables 2 and 3. Comparisons of Properties of Typical Electronic Coolants. [4]

An excellent review of common cold plate fluids is provided by Lytron, an OEM of cold plates and other cooling devices. The following condenses fluid descriptions taken from Lytron’s literature. [5]

The most commonly used coolants for liquid cooling applications today are:

  • Water
  • Deionized Water
  • Inhibited Glycol and Water Solutions
  • Dielectric Fluids

Water – Water has high heat capacity and thermal conductivity. It is compatible with copper, which is one of the best heat transfer materials to use for your fluid path. Facility water or tap water is likely to contain impurities that can cause corrosion in the liquid cooling loop and/or clog fluid channels. Therefore, using good quality water is recommended in order to minimize corrosion and optimize thermal performance. If you determine that your facility water or tap water contains a larger percentage of minerals, salts, or other impurities, you can either filter the water or you can opt to purchase filtered or deionized water. [5,6]

Deionized Water – The deionization process removes harmful minerals, salts, and other impurities that can cause corrosion or scale formation. Compared to tap water and most fluids, deionized water has a high resistivity. Deionized water is an excellent insulator, and is used in the manufacturing of electrical components where parts must be electrically isolated. However, as water’s resistivity increases, its corrosivity increases as well. When using deionized water in cold plates or heat exchangers, stainless steel tubing is recommended. [5, 7]

Inhibited Glycol and Water Solutions – The two types of glycol most commonly used for liquid cooling applications are ethylene glycol and water (EGW) and propylene glycol and water (PGW) solutions. Ethylene glycol has desirable thermal properties, including a high boiling point, low freezing point, stability over a wide range of temperatures, and high specific heat and thermal conductivity. It also has a low viscosity and, therefore, reduced pumping requirements. Although EGW has more desirable physical properties than PGW, PGW is used in applications where toxicity might be a concern. PGW is generally recognized as safe for use in food or food processing applications, and can also be used in enclosed spaces. [5, 8]

Dielectric Fluid – A dielectric fluid is non-conductive and therefore preferred over water when working with sensitive electronics. Perfluorinated carbons, such as 3M’s dielectric fluid Fluorinert™, are non-flammable, non-explosive, and thermally stable over a wide range of operating temperatures. Although deionized water is also non-conductive, Fluorinert™ is less corrosive than deionized water. However, it has a much lower thermal conductivity and much higher price. PAO is a synthetic hydrocarbon used for its dielectric properties and wide range of operating temperatures. For example, the fire control radars on today’s jet fighters are liquid-cooled using PAO. For testing cold plates and heat exchangers that will use PAO as the heat transfer fluid, PAO-compatible recirculating chillers are available. Like perfluorinated carbons, PAO has much lower thermal conductivity than water. [5, 9]

Conclusion

Water, deionized water, glycol/water solutions, and dielectric fluids such as fluorocarbons and PAO are the heat transfer fluids most commonly used in high performance liquid cooling applications.

It is important to select a heat transfer fluid that is compatible with your fluid path, offers corrosion protection or minimal risk of corrosion, and meets your application’s specific requirements. With the right chemistry, your heat transfer fluid can provide very effective cooling for your liquid cooling loop.

References

[1] https://www.aavid.com/product-group/liquidcoldplates/fluid

[2] http://semi-therm.org/wp-content/uploads/2017/04/How-to-design-liquid-cooled-system.pdf

[3] Mohapatra, Satish C., “An Overview of Liquid Coolants for Electronics Cooling,” ElectronicsCooling, May 2006.

[4] http://www.calce.umd.edu/whats_new/2012/Presentations/David %20Saums%20PPt.pdf

[5] http://www.lytron.com/Tools-and-Technical-Reference/Application-Notes/The-Best-Heat-TransferFluids-for-Liquid-Cooling

[6] https://www.thereadystore.com/5-gallon-collapsible-water-container

[7] https://www.amazon.co.uk/IONISED-WATER-Mineralised-DeionisedDistilled/dp/B00X30JKGY/ref=pd_lpo_vtph_263_tr_t_2?_encoding=UTF8&psc=1&refRID=QNAM8H7J8R 1AEDP8W5FF

[8] http://www.rhomarwater.com/products/catalog/envirogard-heat-transfer-fluid-antifreeze

[9] http://www.skygeek.com/anderol-royco-602-cooling-fluid.html