Tag Archives: liquid cooling

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

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.


  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 

Immersion Liquid Cooling of Servers in Data Centers

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.   


  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.

Tubed and Submerged-Fin Cold Plates in Electronics Thermal Management

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.


  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.

Recent Research Into Next-Generation Heat Exchangers for Electronics Thermal Management

Since it was published around one year ago, the “What is a Heat Exchanger” video (watch it below) has been one of the most watched on the ATS YouTube page. With the obvious interest in heat exchangers in particular (and liquid cooling in general), we are curating recent research into the technology and its applications in the thermal management of electronics.

Heat Exchangers
Heat Exchangers are a common component in liquid cooling solutions for electronics. Below is recent research into this growing technology. (Advanced Thermal Solutions, Inc.)

The following are three examples of papers written about heat exchangers including applications in the automotive space to developing microchannels to enhance thermal performance to optimizing heat exchangers for use with high-powered electronics.

We have posted several pieces of content on this blog about heat exchangers in the past. Examples include:

Since heat exchangers remain a popular topic for engineers, we will continue to add new pieces about the technology in the coming months.

Novel Power Electronics Three-Dimensional Heat Exchanger

Read the full paper at https://www.nrel.gov/docs/fy14osti/61041.pdf.

Abstract: Electric-drive systems, which include electric machines and power electronics, are a key enabling technology to meet increasing automotive fuel economy standards, improve energy security, address environmental concerns, and support economic development. Enabling cost-effective electric-drive systems requires reductions in inverter power semiconductor area, which increases challenges associated with heat removal. In this paper, we demonstrate an integrated approach to the design of thermal management systems for power semiconductors that matches the passive thermal resistance of the packaging with the active convective cooling performance of the heat exchanger. The heat exchanger concept builds on existing semiconductor thermal management improvements described in literature and patents, which include improved bonded interface materials, direct cooling of the semiconductor packages, and double-sided cooling. The key difference in the described concept is the achievement of high heat transfer performance with less aggressive cooling techniques by optimizing the passive and active heat transfer paths. An extruded aluminum design was selected because of its lower tooling cost, higher performance, and scalability in comparison to cast aluminum. Results demonstrated a 102% heat flux improvement and a package heat density improvement over 30%, which achieved the thermal performance targets.

Microchannel Heat Exchanger for Electronics Cooling Applications

Read the full paper at http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1636343.

Abstract: The power consumption of electronic devices, such as semiconductor diode laser bars, has continually increased in recent years while the heat transfer area for rejecting the associated thermal energy has decreased. As a result, the generated heat fluxes have become more intense making the thermal management of these systems more complicated. Air cooling methods are not adequate for many applications, while liquid cooled heat rejection methods can be sufficient. Significantly higher convection heat transfer coefficients and heat capacities associated with liquids, compared to gases, are largely accountable for higher heat rejection capabilities through the micro-scale systems. Forced convection in micro-scale systems, where heat transfer surface area to fluid volume ratio is much higher than similar macro-scale systems, is also a major contributor to the enhanced cooling capabilities of microchannels. There is a balance, however, in that more power is required by microchannels due to the large amount of pressure drop that are developed through such small channels. The objective of this study is to improve and enhance heat transfer through a microchannel heat exchanger using the computational fluid dynamics (CFD) method. A commercial software package was used to simulate fluid flow and heat transfer through the existing microchannels, as well as to improve its designs. Three alternate microchannel designs were explored, all with hydraulic diameters on the order of 300 microns. The resulting temperature profiles were analyzed for the three designs, and both the heat transfer and pressure drop performances were compared. The optimal microchannel cooler was found to have a thermal resistance of about 0.07 °C-cm2 /W and a pressure drop of less than half of a bar.

Thermal Analysis of the Heat Exchanger for Power Electronic Device with Higher Power Density

Read the full paper at http://pe.org.pl/articles/2012/12a/70.pdf. Abstract: Liquid cooling system has been used in high power electronic device systems to cool down the temperature of power electronic device. Heat exchanger is an important part of liquid cooling system to transfer the heat generated by power electronic device into air. In this paper, a Streamline-upwind/Petrov-Galerkin (SUPG) stabilized finite element analysis method was proposed to solve the water and air governing formulas including the mass conservation equation, the momentum conservation and the energy conservation equation. Furthermore, the thermal characteristic of a heat exchanger is simulated, and the result was compared with an experiment. The comparison shows that this method is effective.

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.

Technology Review: Liquid Cooling Solutions

(This article was featured in an issue of Qpedia Thermal e-Magazine, an online publication dedicated to the thermal management of electronics. To get the current issue or to look through the archives, visit http://www.qats.com/Qpedia-Thermal-eMagazine.)

Qpedia continues its review of technologies developed for electronics cooling applications. We are presenting selected patents that were awarded to developers around the world to address cooling challenges. After reading the series, you will be more aware of both the historic developments and the latest breakthroughs in both product design and applications.

Liquid Cooling Solutions

The focus of this article is to highlight recent patents for liquid cooling devices. (Advanced Thermal Solutions, Inc.)

We are specifically focusing on patented technologies to show the breadth of development in thermal management product sectors. Please note that there are many patents within these areas. Limited by article space, we are presenting a small number to offer a representation of the entire field. You are encouraged to do your own patent investigation.

Further, if you have been awarded a patent and would like to have it included in these reviews, please send us your patent number or patent application.

In this issue our spotlight is on liquid-based cooling solutions.

There are many U.S. patents in this area of technology, and those presented here are among the more recent. These patents show some of the salient features that are the focus of different inventors.

Liquid Cooling Devices

Embedded Microchannel Cooling Package for a Central Processing Unit

US 7515415 B2, Monfarad, A. and Yang, J.

An indirect cooling liquid embedded package design for use with a computer central processor unit is suitable for thermal management of high heat dissipation electronic components such as server processors. The indirect contact cooling liquid embedded packaged CPU has mechanical coupling and embedded plumbing that attaches to the board pumped liquid supply and indirect cooling of the heat-generating portion of the CPU with an embedded microchannel heat exchanger. The coolant package system for the CPU removes higher levels of heat indirectly from the core of the processors by convective cooling.

Cooling liquid flows into the microchannel piping in the CPU substrate. Cooling liquid continues to flow out of the microchannel piping into a silicon or metallic microchannel heat exchanger that is directly bonded to a silicon die for cooling of the heat-generating portion of the CPU. As a result, an embedded microchannel indirect contact cooling liquid package for a CPU can be utilized to remove substantially higher levels of heat from the core of the processors by forced convective liquid flow through the microchannel heat exchanger attached to the core of the CPU. Cooling liquid is introduced into the package of the server CPU by mechanically attaching the CPU to the board through a socket interconnect. Pins of the socket serve to provide electrical connection between the board and the CPU, while a few pins are designed for the purpose of providing an inlet and an outlet for cooling liquid into and out of the CPU package.

The cooling system of the present invention also uses the existing package-to-board practice of using sockets and therefore the entire cooling system is embedded into the processor-to-board assembly. From the end user’s point of view, there is a tremendous amount of simplification of board design as the bulky fan and heat sink assemblies are removed. The replacement, according to the present invention, is a central liquid cooling system that can be made redundant to substantially prevent any reliability issues in the field.

Planar Heat Pipe for Cooling

US 8305762 B2, Wits, W., Mannak, J. and Legtenberg, R.

The invention claimed is a circuit board for cooling of heat-dissipating components assembled thereon, including at least two panels at least one of which is populated With heat-dissipating components, both panels being metal clad on a side, at least one of the panels being formed from a printed circuit board laminate and comprising a plurality of grooves on its metal clad side, the panels being bonded together by an adhesive layer With their metal clad sides oriented face to face so as to form a circuit board containing a sealed cavity having a height defined by a thickness of the adhesive layer and the separation of the metal clad sides, the cavity being partly filled with a fluid, the fluid circulating by capillary action along the grooves towards zones exposed to heat where the fluid vaporizes.

Vapor may circulate back by pressure gradient effect through the cavity towards zones not exposed to heat where it condenses. In a mode of implementation, the heat pipe may be embedded in a circuit board formed by the panels for inherent cooling of heat-dissipating components.

Thus, key advantage provided by the present invention in any of its aspects is that it is based on most standard processes of multilayer PCB fabrication such as laminating, selective metal plating and etching. Therefore, it is a highly cost-effective solution. Furthermore, the invention provides a very flexible design solution enabling to adapt the cooling paths to the PCB layout, especially to the higher heat dissipation locations. Not requiring any supplementary materials, it is even considerably lighter than a tubular heat pipe-based solution.

Implemented as enhancement of a computer aided engineering tool, heat pipe cooling cavities could be designed concurrently with the layout of components placement and printing of circuits, ensuring optimized thermal management. This enables multilayer PCB assemblies, which are high density electronic devices, to benefit the most from the integrated heat pipe cooling function.

Cooling System for Electronic Equipment

US 7508666 B1, Henneberg, M. and Johnson, L.

A cooling solution includes a system providing thermal energy dissipation for electronic equipment located in support racks or cabinets of a facility. According to one embodiment, the system is integrated with a facility where the support cabinets are located. The system providing thermal energy dissipation includes a cooling loop, a fan unit for moving air across the cooling loop and one or more ducts forming a confined flow pathway for the moving air between the fan unit and cabinets for delivery to the electronic equipment.

More specifically, the cooling loop contains a supply of circulating heat absorbing fluid such that the heat absorbing fluid removes thermal energy from the air moved by the fan unit. Each cabinet is formed with an exhaust pathway such that the moving air enters the cabinet from the duct, flows across the electronic equipment to remove thermal energy therefrom, and exits the cabinet.

Claims include a cooling system for a facility housing electronic equipment, the facility having a support surface on which a cabinet holding the electronic equipment is located, the system comprising: a cooling loop located beneath the support surface and containing a supply of circulating heat absorbing fluid; a fan unit located beneath the support surface and configured to move air across the cooling loop such that the heat adsorbing fluid removes thermal energy from the moving air; at least one duct forming a confined flow pathway for the moving air between the fan unit and the cabinet, wherein the cabinet is formed with a substantially lateral exhaust pathway such that the moving air enters via a back region of the cabinet, flows across the electronic equipment, housed by the cabinets, to remove thermal energy therefrom, and exits a front region of the cabinet; and a chilling plate positioned downstream of the flow of moving air exiting the cabinet such that the chilling plate is located outside of the front region of the cabinet, the chilling plate is coupled to a secondary cooling loop containing a supply of heat absorbing fluid.

Claims also include a method for providing thermal energy dissipation for network-based electronic equipment housed within a plurality of cabinets located on a support surface of a facility, each of the plurality of cabinets having an interior formed with a through passageway extending from an entrance at a first side of each of the plurality of cabinets to an exit at a second side of each of the plurality of cabinets, the method comprising: providing a cooling loop containing a supply of circulating heat adsorbing fluid; providing a fan unit configured to move air across the cooling loop such that the heat adsorbing fluid removes thermal energy from the moving air; directing the moving air from the fan unit to the through passageway of each of the plurality of cabinets such that the moving air flows across the electronic equipment to remove thermal energy therefrom, and exits the plurality of cabinets; and providing a plurality of chilling plates positioned downstream of the flow of moving air exiting the plurality of cabinets such that one of the plurality of chilling plates is located outside of each of the plurality of cabinets, respectively, each of the plurality of chilling plates is coupled to a secondary cooling loop containing a supply of heat absorbing fluid.

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.