Tag Archives: liquid cooling

Making the Change

Posted on July 1, 2026 by | Leave a comment

Air cooling was once the dominant method for cooling processors on a PCB, employing heat sinks, fans, and blowers. These solutions are still popular, but faster-running, higher-powered devices, like most GPUs used for AI can’t be sufficiently cooled with air. Liquid cooling is needed. [1,7]

There isn’t a universal application point where engineers must switch from air cooling to liquid cooling. The decision mainly depends on allowable temperature and heat flux. Other considerations include higher costs and power needs, added hardware, space and weight, and required more monitoring. [1,3]

Fig 1 – Air Cooling Heat Sink vs. Liquid Cooling. [9,10]

In practice, once devices reach several hundred watts in a compact package, or when the required thermal resistance approaches 0.1°C/W or lower, liquid cooling often becomes the preferred solution.

Low Thermal Resistance

Engineers usually don’t switch to liquid cooling simply because a chip reaches a particular wattage. They switch when the required junction-to-ambient thermal resistance falls below what can be achieved economically and reliably with available airflow and heat sink models. [2,3,5]

Fig 2 – Typical Chip Temperature Location [11]

Consider an equation and example:

Tj = Tα+ P x RαJA                              [2]

Where:

Tj = junction temperature

Tα = ambient temperature

P = power dissipation

RαJA = thermal resistance from junction to ambient

If keeping the chip within its temperature limits requires an unrealistically low thermal resistance, air cooling may not be practical.

Example:

Ambient = 40°C

Maximum junction temp = 90°C

Chip power = 500 W

The allowable thermal resistance is:

RαJA = 90 – 40 /500 = 0.1°C/W

Achieving 0.1°C/W with air is extremely difficult. Liquid cooling is the practical solution. [2,3]

High Heat Flux

Heat flux (power per unit area) is often more important than total power. [3]

For example:

  • A 100 W device spread onto a large heat sink may be easy to air-cool
  • A 100 W device concentrated in a 1 cm² die can be much harder

Modern high-performance processors, GPUs, laser diodes, RF power amplifiers, and power electronics often reach heat fluxes that make air cooling difficult.

Fig 3 – Heat Flux Measures the Amount of Heat Energy Transferred from a Warmer Side to a Cooler Side. [12]

Typical industry guidance suggests:

  • Air cooling: comfortable below ~10–20 W/cm² [1,6]
  • Advanced air cooling: can sometimes handle 50–100 W/cm² with aggressive airflow [1,6]
  • Liquid cooling: often becomes attractive above ~100 W/cm² [1,6,7]

In basic terms:

  • Air cooling is usually limited by how much heat you can transfer from the heat sink to the air.
  • Liquid cooling is usually limited by how much heat you can get from the chip into the coolant.

Where Air Cooling Works Well

Fig 4 – Heat Sinks from Advanced Thermal Solutions, Inc. [9]

  • Total heat dissipation is relatively modest, up to a few hundred watts
  • There is enough surface area for heat sinks
  • There is sufficient airflow through the enclosure
  • Higher fan noise is acceptable  [1,3]

Air cooling is used in many consumer electronics products and networking devices.

Coolants Remove More Heat

Since water-based coolants have much higher heat capacity and thermal conductivity than air, they can transport large amounts of heat away with relatively small temperature rises. [3,9]

For example:

  • Air’s specific heat capacity is about 1 kJ/kg·K 
  • Water’s is about 4.2 kJ/kg·K   

And water is about 830 times denser than air, so a small coolant flow can carry away an enormous amount of heat compared with an equivalent volume flow of air. [9]

Fig 5 – Tubing and Ports on a Liquid Cooling System [9]

That’s why modern AI accelerators, high-power motor drives, and high-density data-center servers are increasingly moving toward liquid cooling: not because air cooling is impossible, but because the required heat removal density becomes impractical with fans and heat sinks alone. [1,7,8]

The Benefits of Faster Flow Rates

Air cooling performance increases when the rate of airflow increases. Thus, many heat sinks are supported with fans and blowers to enhance heat transfer into the passing air. [3]

Liquid cooling, similarly, is enhanced with higher flow rates. A common expectation is that a coolant that stays longer at the heat source (chip) will absorb more heat. But, at slower flow rates, the coolant heats up as it moves through a cold plate and downstream in the cooling loop. As a result, the returning coolant has less of a temperature difference from the chip, and heat transfer becomes less effective. [3,4]

With a faster flow of liquid coolant, the fluid temperature stays more uniform and keeps a steady, higher temperature difference from the chip. This makes heat extraction more efficient and improves the lowering of chip temperatures. [3,4]

Flow rates can be optimized per application. There are diminishing returns on performance as flow rates increase, as well as added costs. Your liquid cooling system provider should provide performance data and recommendations for proper flow rates. [3,4]

In-Between Air and Liquid Cooling

There are options that fall between air and liquid cooling methods. Engineers should look through these choices before designing in a liquid system. They could provide simpler, lower-cost, but reliably effective cooling       

The expanded options include:

  1. Better PCB thermal design (thermal vias, thicker copper planes)
  2. Larger heat sinks
  3. Forced-air cooling with optimized airflow paths
  4. Heat pipes or vapor chambers to spread heat
  5. Remote heat exchangers connected by heat pipes
  6. Liquid cold plates       [3,4]

Fig 6 – Heat Pipes May Meet Cooling Needs in Place of Air or Liquid Cooling [9]

Not a Tradeoff

Traditional air cooling is inadequate for many of today’s thermal management needs. Other methods, including enhanced air cooling  systems, may offer solutions. But for many applications, including fast-growing AI units and data centers, liquid cooling is essential. In this case, there is no tradeoff because its use is the only option. [1,6,7]

Consider This

Here are some analogies for comparing air to liquid (water) cooling:

Air is a ghost. Because air is so light and empty, a single cubic meter of it can only grab a tiny handful of heat before it gets too hot and gives up.

Water is a sponge. Because water is about 830 times denser and packed tight with mass, that same one cubic meter acts like a massive thermal sponge. It can swallow up a staggering amount of heat before its temperature rises even a single degree.

To cool a hot system, you either have to blow a hurricane of lightweight air past it, or gently glide a tiny, heavy stream of water over it.

References

  1. ASHRAE. Thermal Guidelines for Data Processing Environments, latest edition.
  2. JEDEC Solid State Technology Association. JESD51 Series: Methodology for the Thermal Measurement of Component Packages.
  3. Frank P. Incropera, David P. DeWitt, Theodore L. Bergman, and Adrienne S. Lavine. Fundamentals of Heat and Mass Transfer, Wiley.
  4. David A. Reay, Ryan McGlen, and Peter Kew. Heat Pipes: Theory, Design and Applications.
  5. Texas Instruments. Thermal Design by Insight, Not Hindsight (Application Report).
  6. Open Compute Project Foundation. Advanced Cooling Solutions documentation.
  7. NVIDIA. Data Center Liquid Cooling technical papers and deployment guides.
  8. National Institute of Standards and Technology (NIST). Thermophysical Properties of Fluids Database.
  9. Advanced Thermal Solutions, Inc., https://www.qats.com
  10. Chatsworth Products, https://www.chatsworth.com/en-us/resources/blogs/2026/5-misunderstood-facts-about-direct-to-chip-liquid-cooling/
  11. Advanced Thermal Solutions, Inc, https://www.qats.com/
  12. EngineerExcel, https://engineerexcel.com/flow-of-heat/

Leave a comment

Posted in Air Cooling, Cold Plates, cooling, Liquid Cooling, Uncategorized

Tagged , , , , , , ,

Cooling Hot Electronics with Cold Plates

Posted on May 14, 2025 by | 2 comments

Cold plates have been used for thermal management since the Apollo moon missions in the 1960s. Today, they serve a critical role in cooling high-performance electronics across many industries.

Power electronic devices generate significant heat, and if their chips exceed safe temperature limits, system reliability and longevity are compromised. Effective thermal management is essential, as lowering a chip’s junction temperature by just 10°C can double its operational life.

Cold plates offer highly efficient, localized cooling by transferring heat from hot components—such as power semiconductors—into a liquid coolant flowing through the plate. The heated liquid then moves to a remote heat exchanger, where it cools before recirculating back to the cold plate.

Compared to forced-air cooling, cold plates deliver superior thermal performance. They are typically smaller, quieter, and lighter than fan-based systems, making them an attractive solution in compact or noise-sensitive environments.

Most cold plates consist of thin-walled aluminum or copper blocks with internal channels or tubing for coolant flow. As liquid moves through the plate, it absorbs heat from the attached components and carries it away for external dissipation. Modern designs often use mini-channels instead of traditional tubing. These intricate internal pathways maximize surface contact with the coolant, improving heat transfer and cooling efficiency.

Figure 1 – Cold Plates are Part of a Liquid Cooling Loop that Includes a Pump for Fluid Circulation and a Heat Exchanger to Remove Heat from the Flowing Coolant. [ATS]

More advanced cold plates feature mini-channels in place of tubing. These designs can better match applications and more efficiently transfer heat into the coolant.

Figure 2 – A Cold Plate with Internal Mini-Channels Provides a High Rate of Thermal Transfer to Remove More Component Heat. [ATS]

Tubed Cold Plates Cool Hot Electronics

Embedded tube designs are the simplest cold plates. They feature a stainless steel or copper tube coiled and set into grooves inside a metal base plate. The tubes can be routed in different pathways to optimize thermal transfer performance. The flowing coolant moves heat from the component, away from the cold plate and over to a heat exchanger where it is cooled before being pumped back to the plate.

Figure 3 – A Tubed Cold Plate Can Consist of Copper or Stainless-Steel Tubing Pressed or Embedded in a Metal Plate. [ATS]

These tubed cold plates are cost-effective solutions for low- to moderate-power applications and are ideal for use in automotive, instrumentation, and UPS systems. ATS offers models ranging from 57–914 mm in length and 57–198 mm in width, with push-to-connect fittings for easy installation.

A variation of this design features thermally conductive epoxy completely covering the tubing and flush with the plate’s surface. This not only improves thermal contact but also provides environmental protection by sealing the tube within the plate.

Figure 4 – A Cold Plate’s Tubing Can be Buried and Covered with a Thermally Conductive Epoxy Layer. [1]

Custom Cold Plates Provide Best Cooling Solutions

For more demanding applications—such as cooling BGAs, LEDs, or high-power modules—custom cold plates offer the best performance. These can include embedded tubing or submerged internal fins, which increase surface area and create turbulence to enhance heat transfer.

Figure 5. Custom Liquid Cold Plate with Inlaid Copper Tubing Provides Heat Transfer Away from Hot Electronics [2]

One example uses tightly spaced aluminum pin fins to generate turbulence with minimal pressure drop, achieving high thermal performance while keeping the plate compact. Another design incorporates internal turbulators tailored for IGBT modules, further improving coolant flow and heat dissipation.

ATS designs and manufactures custom cold plates in collaboration with customers or based on in-house thermal analysis. These designs can include complex internal geometries such as microchannels or gyroid lattices, like the 3D-printed cold plate created for race car IGBT cooling—an approach that improves flow guidance while reducing weight.

Figure 6. Close-spaced Pin Fins with Complex Geometry Create Turbulence with Low Flow Rate Values Inside Submerged Fin Cold Plates. [3]
Figure 7. A Custom IGBT-Cooling Cold Plate Features Internal Turbulators to Optimize Coolant Turbulence and Heat Transfer. [4]

ATS constructs cold plates to customer designs and those developed in partnership with our own thermal engineers. ATS coolant-based cold plates can include internal tubing and microchannels in closed loop systems.

Figure 8. Dual-Sided Cold Plates Cool Components on Both of Their Mounting Sides. [ATS]

Dual-sided high-flow cold plates provide equal cooling performance for components mounted on both sides of the plate, increasing efficiency, space savings and economy. The cold plates can be used with coolant flow rates up to 4 gal/min, and provide thermal resistance as low as 0.0021°C/W. [5]

Figure 9 – This 3D-Printed Metal Cold Plate Cools IGBTs on a Race Car. It Features a Gyroid Lattice That Guides Internal Coolant Flow While Reducing the Overall Weight [6]

DIY Cold Plates Optimize Component Cooling

ATS also offers DIY (do it yourself) cold plates with modular dimensions and pre-defined drill zones. Engineers can customize mounting locations to match specific components. Once the ideal configuration is determined, ATS can mass-produce the cold plate to match exact specifications.

Figure 10 – Do It Yourself Cold Plates from ATS Feature Drill Zones for Precision Matching to Heat Sources, and No Drill Zones to Protect Internal Coolant Flow Channels. [ATS]

The Complete Liquid Cooling Loop

Cold plates are just one part of a complete liquid cooling system. As electronics demand more efficient cooling, liquid-based systems are increasingly replacing air-based solutions. A functional loop includes a pump, reservoir, and heat exchanger to remove heat from the circulating fluid.

Figure 11 – A Liquid Cooling Loop Featuring Cold Plates. This is Implemented in Avionics on F-16 Fighting Falcon Jets. [7]

These systems are becoming more cost-effective and safer, making liquid cooling viable for a broader range of applications. Cold plates serve as a critical stage in these loops, offering simplicity, versatility, and high thermal performance.

Plug and Play Liquid Loops

For streamlined implementation, ATS offers the Industrial Cooling Distribution Module™ (iCDM™)—a fully integrated liquid cooling loop in one compact, portable unit. It includes the pump, heat exchanger, reservoir, precision controls, and monitoring displays, eliminating the need to purchase and configure components separately.

Figure 12 – The New Industrial Cooling Distribution Module Contains the Pump, Heat Exchanger, Reservoir and Controls for Managing Coolants in Liquid Cooling Loops. [ATS]

The iCDM connects directly to cold plates or chassis-based cooling systems. It supports models with cooling capacities of 10 kW and 20 kW, each holding up to 2 liters of coolant. The system is compatible with a wide range of wetted materials, allowing flexible deployment across industries. A next-generation iCDM, available soon, is fully automated, with significantly increased cooling capacities up to 1.4MW.

Conclusion

Cold plates can provide essential electronics cooling because of their design versatility and the power of liquid cooling. AI chip cooling cold plates will soon be available for this growing and demanding arena.

ATS engineers are experts in matching thermal solutions to system needs, offering a wide portfolio that includes cold plates, vapor chambers, coolant chillers, and complete liquid loop systems. Whether liquid cooling is the best solution depends on the specific application, and ATS provides detailed analysis to help customers make informed decisions.

References

  1. Wakefield Thermal, http://www.wakefield-vette.com/products/liquid-cooling/liquid-cold-plates/standard-liquid-cold-plates.aspx
  2. Baknor, https://www.baknorthermal.com/liquid-cold-plates-various-channel-options/
  3. COOLTECH, http://www.cooltech.it/products/liquid-cold-plates/
  4. Boyd Corp., https://www.boydcorp.com/thermal/liquid-cooling-systems/liquid-cold-plates.html
  5. ATS, https://www.qats.com/Products/Liquid-Cooling/Dual-Sided-Cold-Plates
  6. nTop, https://www.ntop.com/resources/case-studies/cold-plate-automotive-power-electronics/
  7. ThermOmegaTech, https://www.tot-ad.com/avionics-cooling/

2 Comments

Posted in Cold Plates, Liquid Cooling

Tagged , , , , , , , , , , ,

3-D-printed Heat Exchangers provide flexibility in thermal management

Posted on June 7, 2019 by | 4 comments

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

Additive manufacturing technologies have expanded in many directions in recent years with applications ranging across numerous industries and applications, including into the thermal management of electronics. As metal 3-D printing techniques have improved and become commercially viable, engineers are using it to create innovative cooling solutions, particularly heat exchangers.

3-D Printed Heat Exchangers
Figure 1. 3-D developed heat exchangers can feature shapes not obtainable using traditional forming methods. [2]

Why are engineer turning to additive manufacturing?

One reason is that additive manufacturing allows for generous cost savings. Companies can reduce 15-20 existing part numbers and print them as a single component. A single part eliminates inventory, additional inspections, and assemblies that would have been necessary when components were produced individually.

As AdditiveManufacturing.com notes, “Some envision AM (additive manufacturing) as a complement to foundational subtractive manufacturing (removing material like drilling out material) and to a lesser degree forming (like forging). Regardless, AM may offer consumers and professionals alike, the accessibility to create, customize and/or repair product, and in the process, redefine current production technology.” [1]

Developed at the Massachusetts Institute of Technology (MIT), 3-D printing is the most common and well-known form of additive manufacturing. Three-dimensional objects are made by building up multiple layers of material. Thanks to the continued (and rapid) development of the technology and advanced research in materials science, the layers can be composed of metal, plastic, concrete, living tissue or other materials.

In industrial applications, 3-D printing has encouraged creativity. With additive manufacturing, designers can create complex geometric shapes that would not be possible with standard manufacturing processes. For example, shapes with a scooped out or hollow center can be produced as a single piece, without the need to weld or attach individual components together. One-piece shapes can provide extra strength, with few or no weak spots that can be compromised or stressed. [4]

Making 3-D Printed Heat Exchangers

Heat exchangers are integral to thermal management. Any time heat, cool air, or refrigeration are required, a heat exchanger has to be involved to dissipate the heat to the ambient. This can be as simple as a standard heat sink or a complex metal structure used in liquid cooling. It can be as small as a few millimeters or as large as a building. Heat exchange is a multi-billion-dollar industry touching everything from consumer goods to automotive and aerospace engineering.

Compact heat exchangers are typically composed of thin sheets of material that are welded together. The complexity of the designs, particularly the density of the fin field, makes production both challenging and time-consuming, while the material used for the welding process adds to the overall weight of the part. Heat exchangers produced through 3-D printing techniques (such as those pictured below) can be made quicker, lighter, and more efficiently.

Figure 2. 3-D developed heat exchanger had a 20% increase in efficiency. [2]

In 2016, a Department of Energy-funded consortium of researchers developed a miniaturized air-to-refrigerant heat exchanger that was more compact and energy-efficient than current market designs. CEEE and 3-D Systems teamed to increase the efficiency of a 1 kW heat exchanger by 20 percent while reducing weight and size. The manufacturing cycle for the heat exchanger was reduced from months to weeks. [4]

Figure 3. A 3-D printed milli-structured heat exchanger made from stainless steel with a gyroid design. [5]

Using direct metal printing (DMP), manufacturers delivered a 20-percent more efficient heat exchanger and an innovative design. It was produced in weeks not months and with significantly lower weight. The one-part, 3-D-printed heat exchanger required minimal secondary finishing operations.

Ohio-based Fabrisonic uses a hybrid metal 3-D printing process, called Ultrasonic Additive Manufacturing (UAM), to merge layers of metal foil together in a solid-state thanks to high frequency ultrasonic vibrations. [5]

Figure 4. Aluminum and copper heat exchanger printed using ultrasonic additive manufacturing. (Photo via Fabrisonic) [6]

Fabrisonic mounts its hybrid 3-D printing process on traditional CNC equipment – first, an object is built up with 3-D printing, and then smoothed down with CNC machining by milling to the required size and surface. No melting is required, as Fabrisonic’s 6 ft. x 6 ft. x 3 ft. UAM 3-D printer can scrub metal foil and build it up into the final net shape, and then machines down whatever else is needed at the end of the process.

This 3-D printing process was recently given a stamp of approval by NASA after testing at the Jet Propulsion Laboratory (JPL). A report from NASA and Fabrisonic said, “UAM heat exchanger technology developed under NASA JPL funding has been quickly extended to numerous commercial production applications. Channel widths range from 0.020 inch to greater than one inch with parts sized up to four feet in length.” [6]

There are challenges involved, to be sure. In an article from Alex Richardson of Aquicore highlighting research done at the University of Maryland, researchers discuss the problems that 3-D printing still has competing on price against traditional manufacturing techniques and the difficulties involved with physically scaling a technology up.

In the article, Vikrant Aute of the University of Maryland Center for Environmental Energy Engineering noted that his research team was “considering modularization to overcome the latter issue: Instead of making the exchangers bigger, it might be possible to arrange lots of them together to accomplish the same task.” [7]

Research Continues to Improve 3-D Printing Process

While there have been numerous advancements in the technology of metal 3-D printing, research is continuing on campuses and in companies around the world to try and improve the process and make it easier to create increasingly complex heat exchangers.

For example, Australia-based additive manufacturing startup Conflux Technology received significant funding to develop its technology specifically for heat exchange and fluid flow applications. [8] Another example was the University of Wisconsin-Madison, which received a grant from the U.S. Department of Energy (DOE) Advanced Research Projects Agency-Energy (ARPA-E) to build heat exchangers with “internal projections to increase turbulence and facilitate heat transfer. Such intricate shapes are impossible with traditional manufacturing.” [9]

In 2018, U.K.-based Hieta Technologies partnered with British metrology company Renishaw to commercialize its 3-D-printed heat exchangers. Renishaw used its AM250 system to 3-D print walls of the heat exchanger as thin as 150 microns. The samples were heat treated and characterized to confirm that the laser powder bed fusion process was effective. The process took only 80 hours, was 30 percent lighter, and had 30 percent less volume, while still meeting the heat transfer and pressure drop requirements. [10, 11]

Last month, GE Research announced that it was leading a multi-million-dollar program with Oak Ridge National Laboratory (ORNL) and the University of Maryland to develop compact heat exchangers that can withstand temperatures as high as 900°C and pressures as high as 250 bar. This was also based on funding from ARPA-E, as part of its HITEMMP (High-Intensity Thermal Exchanger through Materials and Manufacturing Processes) program. [12]

3-D Printed Heat Exchangers
Fig. 5. GE Research is leading a project to design a new, high-temperature heat exchanger with 3-D printing. [12]

To build the new heat exchanger, GE engineers are using a novel nickel superalloy that is designed for high temperatures and is crack-resistant. University of Maryland researchers are working with GE to create biological shapes that will make the heat exchanger more efficient and ORNL researchers are providing corrosion resistance expertise to develop the materials for long-term use.

These are just some examples of the many ways that 3-D printing has impacted electronics cooling. Researchers at the Fraunhofer Institute for Laser Technology ILT in Germany have demonstrated the feasibility of 3-D printing copper [13], U.K. researchers 3-D printed “smart materials” for energy storage [14], a researcher at Penn State (soon to be at MIT) is developing methods for creating rough surfaces through additive manufacturing to enhance boiling heat transfer [15], and at Virginia Tech researchers developed a new process for 3-D printing piezoelectric materials [16].

The technology is growing by leaps and bounds each year and is enhancing the options for engineers in the thermal management industry.

References

  1. http://additivemanufacturing.com/basics/
  2. https://www.3-Dsystems.com/learning-center/case-studies/direct-metal-printing-dmp-enables-ceee-manufacture-lean-and-green-heat
  3. https://www.spilasers.com/application-additive-manufacturing/additive-manufacturing-a-definition/
  4. https://www.3-Dsystems.com/learning-center/case-studies/direct-metal-printing-dmp-enables-ceee-manufacture-lean-and-green-heat
  5. http://fabrisonic.com/ultrasonic-additive-manufacturing-overview/
  6. https://aquicore.com/blog/3-D-printing-heat-exchangers/
  7. https://cdn2.hubspot.net/hubfs/3985996/Articles%20-%20published/NASA%20HX%20White%20Paper%20EWI.pdf
  8. https://www.confluxtechnology.com
  9. https://www.engr.wisc.edu/researchers-bring-3d-printing-cool-industry/
  10. https://3dprint.com/198933/hieta-renishaw-heat-exchangers/
  11. https://www.youtube.com/watch?v=r42Dc_PKBEc
  12. https://www.ge.com/research/newsroom/ge-researchers-utilize-3d-printing-design-ultra-performing-heat-exchanger-more-efficient
  13. https://www.ilt.fraunhofer.de/en/press/press-releases/press-release-2017/press-release-2017-08-30.html
  14. https://www.qmul.ac.uk/media/news/2018/se/scientists-design-material-that-can-store-energy-like-an-eagles-grip.html
  15. https://news.psu.edu/story/574464/2019/05/15/academics/heat-transfer-additive-manufacturing-powers-nsf-graduate-research
  16. https://vtnews.vt.edu/articles/2019/01/3d_printing_discovery.html

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com. To register for Qpedia and to get access to its archives, visit 
https://www.qats.com/Qpedia-Thermal-eMagazine.

4 Comments

Posted in Heat Exchangers, Liquid Cooling

Tagged , ,

Immersion Liquid Cooling of Servers in Data Centers

Posted on March 26, 2019 by | 1 comment

A data center is a large infrastructure used to house large quantities of electronic equipment, such as computer servers, telecommunications equipment, and data storage systems, etc. The data center requires non-interrupted power, communication and internet access to all equipment inside, it also has dedicated environment control system which provides appropriate working conditions for the electrical devices hosted inside.

Immersion Cooling

Traditional data centers use cold air generated by a room air conditioner system (CRAC) to cool the servers installed on the racks. Cooling the electrical devices by cold air generated by an air conditioner is an easy method to implement. However, it is not a very efficient method in terms of power consumption.

The inefficiency of the method can be contributed to several causes: generating and delivering cold air from a chiller to servers is a multiple heat transfer process, such as the mixing of warm and cool air in the room, which reduces the efficiency and power consumption of cooling hardware such as chillers, computer room air conditioners (CRACs), fans, blowers and pumps.

Data center designers and operators have invented many ways to improve the data center’s thermal efficiency, such as optimizing the rack layout and air conditioner location, separating cold aisles and hot aisles, optimizing the configuration of pipes and cables in under-floor plenum, introducing liquid cooling to high-power severs.

While the above methods can improve the data center heat load management, they cannot dramatically reduce the Power Usage Effectiveness (PUE), which is a measure of how efficiently a datacenter uses its power and is defined as the ratio of total datacenter power consumption to the IT equipment power consumption.

An ideal PUE is 1,0. A better way, proposed and used by some new data centers, is directly bringing the outside cold air to the servers. This method can eliminate the computer room air conditioners (CRACs). To achieve this, the data center has to be located in a specific area where cold air can be provided for all four seasons and the servers have to have higher operating environmental temperature.

Another dramatic solution proposed and used by some companies is liquid immersion cooling for entire servers. When compared with traditional liquid cooling techniques, the liquid immersion cooling uses dielectric fluid as a working agent and open bath design. This eliminates the need for hermetic connectors, pressure vessels, seals and clamshells. There are several different liquid immersion cooling methods.

This article will review the active single-phase immersion cooling technology proposed by Green Revolution Cooling (GRC) [1] and a passive two-phase immersion cooling technology proposed by the 3M Company [2].

Green Revolution Cooling has designed a liquid-filled rack to accommodate the traditional servers and developed dielectric mineral oil as the coolant. Figure 1 shows the liquid cooling racks with chiller and an inside view of a CarnotJet cooling rack from GRC. The racks are filled with 250 gallons of dielectric fluid, called GreenDEF™, which is a non-toxic, clear mineral oil with light viscosity.

Figure 1. Server racks and chiller (left) and inside view of the server rack. [1]

The servers are installed vertically into slots inside the rack and fully submerged in the liquid coolant. Pumps are used to circulate the cold coolant from the chiller to the rack. The coolant returns to the chiller, after removing heat from the servers. Because of its high heat capacity and thermal conductivity, the GreenDEF™ can cool the servers more efficiently than air.

The server racks are semi-open to the environment and the coolant level is constantly monitored by the system. Figure 2 shows a server motherboard is being submerged in the coolant liquid inside a server rack from GRC.

Figure 2. A Server Motherboard Being Immersed in Liquid Coolant in A Server Rack. [1]

Intel has conducted a year-long test with immersion cooling equipment from Green Revolution Cooling in New Mexico [3]. They have found that the technology is highly efficient and safe for servers. In their tests, Intel tested two racks of identical servers – one using traditional air cooling and the other immersed in a Green Revolution enclosure. Over the course of a year, the submerged servers had a partial Power Usage Effectiveness (PUE) of 1.02 to 1.03, equaling some of the lowest efficiency ratings reported using that metric.

The 3M Company is also actively engaged in immersion cooling technology and has developed a passive two-phase immersion cooling system for servers. Figure 3 illustrates the concept of the immersion cooling system developed by 3M. In a specially designed server rack, servers are inserted vertically in the rack. The servers are immersed in 3M’s Novec engineered fluid, a non-conductive chemical with a low boiling point.

The elevated temperature of electronic components on the sever boards will cause the Novec engineered fluid to boil. The evaporation of the fluid will remove a large amount of heat from the heated components with small temperature difference. The evaporated fluid travels to the upper portion of the server rack, where it condenses to liquid on the surface of the heat exchanger cooled by the cold water. The condensed liquid flows back to the rack bath, driven by the force of gravity. In 3M’s server rack, the liquid bath is also semi-open to the outside environment.

Because the cooling method is passive, there is no pump needed in the system.

Figure 3. Passive Two-phase Immersion Cooling System from 3M. [2]

By utilizing the large latent heat of Novec engineered fluid during evaporation and condensation, the coolant can remove heat from servers and dissipate it to water heat exchanger with small a temperature gradient. To enhance the boiling on the component surfaces, 3M invented special coating for electronic chips inside the liquid bath. The boiling enhancement coating (BEC) is a 100 mm thick porous metallic material.

The application of the BEC is illustrated in Figure 4. The coating is directly applied to the integrated heat spreader (IHS) of the chip. Tuma [2] claimed that the coating can produce boiling heat transfer coefficients in excess of 100,000 W/m2-K, at heat fluxes exceeding 300,000 W/m2.

Figure 4. Application of boiling enhanced coating (BEC). [2]

In his paper, Tuma [2] discussed the economic and environmental merits of the passive two-phase immersion cooling technology for cooling data center equipment. He concluded that liquid immersion cooling can dramatically decrease the power consumption for cooling relative to traditional air-cooling methods. It can also simplify facility construction by reducing floor space requirements, eliminating the need for air cooling infrastructure such as plenum, air economizers, elevated ceilings etc.

Green Revolution Cooling and 3M have demonstrated the feasibility and applicability of using immersion cooling technology to cool the servers in data centers. The main advantages of immersion liquid cooling are saving overall cooling energy and maintaining the component temperature low and uniform. However, both immersion liquid cooling technologies require specially designed sever racks. Specially formulated coolants are needed for both cooling technologies, too, and they are not cheap. For the traditional air-cooled data center, the air is free, abundant and easy to deliver.

In both immersion cooling technologies, the servers have to be vertically installed inside the server rack, which will reduce the date center footprint usage efficiency. Because the liquid baths used in immersion cooling are open to the environment, coolant is gradually and inevitably lost to the ambient during long term service.

The environmental impact of the discharge of a large amount of coolant by data centers has to be evaluated, too. The effect of the coolant on the connectors and materials used on the PCB is not also very clear.

Immersion liquid cooling is a very promising technology for cooling high-power servers. But, there are still obstacles that need to be overcome before their large scale application is assured.   

References

  1. http://www.grcooling.com
  2. Tuma, E. P., “The Merits of Open Bath Immersion Cooling of Datacom Equipment,” 26th IEEE SEMI-THERM Symposium, Santa Clara, California, USA  2010.
  3. http://www.datacenterknowledge.com

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com.

1 Comment

Posted in Liquid Cooling, Servers

Tagged , , ,

Tubed and Submerged-Fin Cold Plates in Electronics Thermal Management

Posted on February 26, 2019 by | 1 comment

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

Many of today’s electronic devices need the performance of liquid cooling to meet the thermal demands of certain hot components. Liquid cold plates are common cooling systems in high power lasers, fuel cells, battery coolers, motor drives, medical equipment, avionics and other high-power, high-heat flux applications.

Cold Plates
Figure 1. A Custom liquid cold plate design by D6 Industries. [1]

Cold plates provide localized cooling by transferring heat from a device to a liquid that flows to a remote heat exchanger and dissipates into either the ambient or to another liquid in a secondary cooling system. Component heat flows by conduction through a thermal interface material and the metal plate to the metal tubing. Then it flows by convection from the internal surface of the fluid path material into the flowing coolant.

A cold plate in electronics cooling is often an aluminum block with an embedded, coolant-filled metal tube. Another common cold plate type is made with metal shells that are brazed or friction-welded together and filled with a liquid coolant.  On the inside, the metal shells have integral cooling fins that are submerged in the coolant.

Tubed Cold Plates

Embedded tube designs are the simplest version of cold plate cooling devices. They feature a continuous tube set into grooves in a metal plate, and are often bonded in place with thermal epoxy. The flowing coolant moves heat from the component away from the cold plate to a heat exchanger, where it is cooled before being pumped back into the plate. 

A common example of a tubed cold plate features an aluminum plate with an exposed copper tube. The tubes can be routed in different pathways to optimize the thermal performance.

The tubing can be continuous or constructed from straight tubes connected by soldered joints, though joints may increase the potential for leakage.

Figure 2. A Tubed cold plate consists of copper or stainless-steel tubing pressed into a metal plate. [2]

This design can provide a cost-effective thermal solution for component cooling where the heat load is low-to-moderate. Tubed cold plates ensure minimum thermal resistance between the power device and the cold plate by placing the coolant tube in direct contact with the power device’s base. Direct contact reduces the number of thermal interfaces between device and fluid, thus increasing performance for the application.

A variant of this design features a thermal epoxy completely applied over the pressed in tubing and flush with the metal plate surface. These are sometimes called buried tube liquid cold plates. This provides a gap-free thermal interface between the tube and the plate. The epoxy layer protects from any leakage from the metal tube. Another key feature is that that fully buried tube is not exposed to the outside environment.

Figure 3. A buried tube cold plate’s metal tube is covered with a conductive epoxy layer. [3]

The choice of liquid coolant affects thermal performance as well. Choosing the right coolant depends to a great extent on the tube material. Copper tubes are compatible with water and most other common coolants, while stainless steel tubes can be used with deionized water or corrosive fluids.

One cold plate OEM offers a proprietary technology with a tube locking system and pressing techniques that ensure the tube is flush with the plate surface, providing good thermal contact with the component being cooled. This manufacturing method eliminates the need for thermal epoxy between the tube and plate which improves thermal performance. [4]

Submerged Fin Cold Plates

Another type of cold plate is an all-metal construction with brazed or friction welded internal fin field.

Figure 4. Standard, liquid coolant-containing metal cold plate [5]

The integral, internal fins increase the surface area that contacts the fluid and enhances heat transfer. Fin shape and fin density affect the performance of heat exchangers and cold plates. By their geometry, the fins also create turbulence, which minimizes the fluid boundary layer and further reduces thermal resistance.

One high-performance version features tightly packed aluminum pin fins that create turbulence with low flow rate values, resulting in high thermal performance with low pressure drop. In this design, the high density of the internal fins increases the heat transfer area without adding bulk to the cold plate assembly. [6]

Figure 5. Close-spaced pin fins with complex geometry create turbulence with low flow rate values inside submerged fin cold plates. [6]

In most high-performance applications, fins are made of copper or aluminum. Aluminum fins are preferred in aircraft electronic liquid cooling applications due to their lighter weight. Copper fins are mostly used in applications where weight is not an important factor, but compatibility with other cooling loop materials is.

For submerged-fin cold plates, many different fin geometries can be tested to find the best improvement in performance. Some of the most commonly used are louvered, lanced offset, straight, and wavy fins.

Figure 6. Fin designs for submerged-fin cold plates. Clockwise from top: louvered, lanced offset, wavy, and straight fins. [7]

With cooling requirements increasing in many areas of electronics, engineers are turning to liquid cooling to replace air cooling. Lower cost, safer liquid cooling systems have also spurred the trend to liquid cooling.

The prime example is the cold plate – relatively simple in design, affordable, available in alternative versions, and extremely customizable. Cold plates should be considered wherever thermal performance above air cooling is needed.

References:

  1. https://d6industries.com/portfolio/custom-designs-liquid-cold-plate-hydroblock/
  2. https://www.lytron.com/Cold-Plates
  3. http://www.wakefield-vette.com/products/liquid-cooling/liquid-cold-plates/standard-liquid-cold-plates.aspx
  4. https://www.lytron.com/Tools-and-Technical-Reference/Application-Notes/Assessing-the-Quality-of-a-Tubed-Cold-Plate
  5. https://www.qats.com/Products/Liquid-Cooling/Cold-Plates
  6. http://www.cooltech.it/products/liquid-cold-plates/
  7. https://www.lytron.com/Tools-and-Technical-Reference/Application-Notes/Fins-for-Cooling-Success

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or ats-hq@qats.com. To register for Qpedia and to get access to its archives, visit https://www.qats.com/Qpedia-Thermal-eMagazine.


1 Comment

Posted in Cold Plates

Tagged ,