Author Archives: Josh Perry

Technology Review: Spray Cooling

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.

Spray Cooling
This Technology Review will focus on recent developments in spray cooling technology. (Wiklmedia Commons)

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 spray cooling for electronics thermal management.

There are several US 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.

Full Coverage Spray and Drainage System and Method for Orientation-Independent Removal of High Heat Flux

 US 8550372 B2 – Timothy A. Shedd and Adam G. Pautsch

A cooling system and method that significantly improves spray evaporative cooling by using arrays of slot or plane sprays to create coverage of the entire heated surface to be cooled without allowing interaction between plumes that are spraying from the nozzles. The sprays are directed at an angle to the surface to take advantage of the high droplet momentum possessed by the spray to direct a flow of coolant fluid across the surface toward desired draining points, thereby enabling drainage regardless of the orientation of the unit.

The present invention provides a spray cooling system and method that significantly improves spray evaporative cooling by creating a directed momentum flow of cooling fluid across a surface to be cooled. In accordance with the present invention, a spray of cooling fluid is directed directly onto the surface of a work piece to be cooled at an angle with respect to the work piece surface so as to create a flow of cooling fluid in a substantially single direction along the work piece surface. The spray of cooling fluid preferably may be delivered via a plurality of generally fan shaped sprays. The sprays are positioned and aligned to create cooling fluid coverage of the entire heated surface to be cooled without allowing interaction between the spray plumes in a manner that may cause areas of cooling fluid stagnation on the surface.

A full coverage spray and drainage system in accordance with the present invention may be implemented in an otherwise conventional spray cooling system including a reservoir of an appropriate cooling fluid (e.g., Fluorinert-72 for the cooling of electronic circuitry, preferably saturated with a non-condensable inert gas, such as nitrogen), a pump for delivering the cooling fluid under pressure from the reservoir to a spray chamber to be sprayed therein from nozzles onto the work piece to be cooled, and appropriate filtering, metering, and control systems. Cooling fluid is returned from the spray chamber to the coolant reservoir via a drainage point or points in the spray chamber.

In accordance with the present invention, the drainage point or points in the spray chamber may be positioned with respect to the coolant spray such that the flow of cooling fluid directed in a substantially single direction along the work piece surface also is directed toward the drainage point or points. Thus, the cooling fluid momentum directs the fluid toward the drainage point, thereby assuring proper drainage of the cooling fluid despite changes in the orientation of the cooling system.

Directly Injected Forced Convection Cooling for Electronics

US 8824146 B2 – Gerrit Johannes Hendrikus Maria Brok, Wessel Willems Wits, Jan Hendrik Mannak and Rob Legtenberg

Electronic circuitry includes a circuit board and at least one component mounted on the circuit board, with the at least one component generating heat while in use. The circuit board includes one or more apertures aligned with one or more respective components, and the electronic circuitry is configured to provide, while in use, a path for coolant fluid to flow through each aperture and past the respective component.

By providing at least one aperture aligned with a component that generates heat in use, improved cooling of the electronic circuitry may be provided, as cooling effects can more efficiently be targeted at those parts of the circuitry that generate or dissipate heat.

Each aperture may be, but is not necessarily positioned at that point or within that region of the circuit board that is a minimum distance from the component or a respective one of the components.

The central axis of each aperture may be, but is not necessarily, perpendicular to the plane of the circuit board and at least one component. Preferably each aperture is arranged such that a straight line extending out of the aperture along the central axis of the aperture would pass through the component with which the aperture is aligned. Preferably each aperture is arranged such that, in use, coolant fluid exits the aperture towards the component with which the aperture is aligned.

The coolant fluid may be liquid or gas. The coolant fluid may be water. The coolant fluid may comprise a dielectric fluid, for example poly-alpha-olefin (PAO), or an inert gas, for instance nitrogen. Preferably the coolant fluid is air. In some circumstances, the coolant fluid may be supplied from a pressurized source, for instance a pressurized gas cylinder.

The position of each aperture may be such that, in use, coolant fluid passing through the aperture approaches the surface of the component with which the aperture is aligned from a perpendicular direction.

Thereby a jet impingement effect may be provided such that, preferably, the coolant fluid breaks through a respective thermal boundary layer next to the or each at least one heat generating component. Such thermal boundary layers are stable layers of air or other fluid which may build up next to the or each component and which exhibit a temperature gradient away from the component. The presence of such thermal boundary layers can reduce convective cooling effects.

Narrow Gap Spray Cooling in a Globally Cooled Enclosure

US 8174828 B2 – Charles L. Tilton, Donald E. Tilton, Randall T. Palmer, William J. Beasley, Douglas W. Miller and Norman O. Alder

Electronic circuit boards are arranged as respective parallel pairs defining a narrow gap there between. One or more such pairs of boards are supported within a hermitically sealable housing and cooled by way of spraying an atomized liquid coolant from a plurality of nozzles into each narrow gap. Transfer of heat from the circuit boards results in vaporization of at least some of the atomized liquid within the narrow gap. The housing further serves to guide a circulation of vapors out of each narrow gap, back toward the nozzles, and back into each narrow gap. A heat exchanger exhausts heat from the housing and overall system, wherein vapor is condensed back to liquid phase during contact and heat transfer therewith. Condensed liquid is collected and re-pressurized for delivery back to the nozzles such that a sustained cooling operation is performed.

One embodiment provides for a system, including a first entity and a second entity that are respectively disposed such that they define a narrow gap between them. The system also includes at least one nozzle, wherein the nozzle is configured to spray an atomized liquid so that a flow of the atomized liquid and a vapor is induced through the narrow gap. The system also includes a heat exchanger that is configured to condense some of the vapor to liquid, the condensed vapor defining a condensate. The system further includes a housing configured to guide a circulation of at least some of the vapor, which is flowing out of the narrow gap, away from the heat exchanger and into proximity with the at least one nozzle.

Another embodiment provides for a system, the system comprising a housing configured to selectively open-ably enclose a plurality of electronic circuit boards. The system further includes a plurality of electronic circuit boards supported in the housing, wherein at least some of the electronic circuit boards are arranged to define respective pairs of boards. At least one pair of boards defines a narrow gap there between. The system also includes at least one nozzle associated with each narrow gap, each nozzle being configured to spray an atomized liquid into the narrow gap defined by the associated pair of boards. The housing is also configured to guide a circulation of a vapor exiting each narrow gap into proximity with the at least one nozzle associated with the at least one narrow gap.

Still another embodiment provides an apparatus. The apparatus includes a nozzle configured to spray an atomized liquid in a generally conical distribution pattern. The apparatus further includes a re-shaper that is configured to reform the spray of atomized liquid into a generally planar distribution pattern.

Enhanced Spray Cooling Technique for Wedge Cooling

US 8729752 B2 – Balwinder Singh Birdi, Simon Waddell and William Scherzinger  

The present invention relates to apparatus and methods for heat removal and, more particularly, apparatus and methods for spray cooling a wedge of a generator rotor.

In generators, electromagnetic losses occur in the magnetic iron and the copper. These losses result in production of heat which must be removed to maintain overall temperature below that allowable for the copper coating and the insulation used in the construction of the generators. The rotor core, which is made of magnetic iron, can be conduction cooled by flowing fluid through the rotor shaft. However, the removal of heat from copper is better managed if oil is passed through the hollow wedges. Due to lower thermal resistance, the flow of fluid in the vicinity of copper is much more effective in removing heat from the copper and in keeping the overall temperature below the allowable limit. This is done with conduction mode of heat removal.

Since the heat transfer coefficient (HTC) depends upon the velocity of the fluid, the removal of heat is not very efficient, and a very high flow is needed to create a reasonable HTC for conduction cooling. Further, because the rotor is a rotating component, having a large amount of fluid at a radius away from the rotor shaft is not desirable, especially for high powered larger diameter and high-speed machines.

In one aspect of the present invention, a spray cooling manifold comprises a manifold ferrule adapted to circumscribe a shaft of a rotating machine; a manifold pipe having a bend of about 90 degrees having a first end attached to the manifold ferrule and a second, opposite end; a cooling fluid channel running from an inside surface of the manifold ferrule to the second, opposite end of the manifold pipe; and a pipe extending from the second, opposite end of the manifold pipe, the pipe adapted to extend into a wedge of the rotating machine, the pipe having a plurality of holes formed there along.

In another aspect of the present invention, a rotating machine rotor comprises a shaft; a plurality of coils disposed on the shaft; a plurality of wedges disposed between the coils; bands securing the wedges on the rotor; and a manifold comprising a manifold ferrule adapted to circumscribe the shaft; a plurality of manifold pipes, each having a bend of about 90 degrees, each having a first end attached to the manifold ferrule and a second, opposite end attached to a wedge pipe extending into the wedges; a cooling fluid channel running from an inside surface of the manifold ferrule to the wedge pipe; and a plurality of holes disposed along the wedge pipe.

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit or contact ATS at 781.769.2800 or To register for Qpedia and to get access to its archives, visit

Cooling News: New Thermal Products Showcase

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

In this article, Qpedia will explore some innovative thermal management products that have recently hit the market. These new thermal products encompass a variety of thermal management applications from CPU coolers to thermal interface materials (TIM) to sensors and test instruments to advanced materials and concepts.

Graphene Sheets

Cooling News

Paragraf, a group affiliated with the University of Cambridge is producing graphene at up to eight inches (20cm) in diameter, large enough for commercial electronic devices. Engineers at Paragraf are creating graphene wafers and graphene-based electronic devices that can be used in transistors, where graphene-based chips could deliver speeds more than ten times faster than silicon chips.

They can also be used in chemical and electrical sensors, where graphene could increase sensitivity by a factor of more than 30. Paragraf’s devices will target markets including transistors, chemical and electrical sensors, and new energy generation devices.

QSFP-DD BiPass Thermal Cooling Configuration 

Molex, a global electronic solutions provider, highlights its new BiPass thermal management configuration cooling QSFP-DD modules up to 20 W with a 15°C change from the ambient temperature. First shown at DesignCon 2019, the Molex QSFP-DD thermal solution can cool a range of 15W to 20W in different configurations. The BiPass solution allows higher wattage modules to be cooled and will help designers on the path toward 112 Gbps.

As the industry is readying for the launch of next-generation copper and optical QSFP-DD transceivers, thermal management strategies are critical. During the demonstration, Molex showcased a QSFP-DD belly-to-belly BiPass configuration, QSFP-DD belly-to-belly SMT configuration, 2×1 QSFP-DD stacked configuration and 1×2 QFSP-DD BiPass in a vertical orientation with dual heat sinks.

Running at 15W, all configurations were able to cool at less than 25-degree Celsius delta T rise. The BiPass solution routes high-speed signals through Temp-Flextwinax cables enabling greater channel margin compared to PCB alone and allows for a second heat sink on the bottom side of the cage to make contact with the module, providing additional cooling.

The BiPass solution, allows designers to bypass the lossy printed circuit board by utilizing Temp-Flex high-speed twinax. Because of this, they can achieve lower insertion loss when going from an ASIC in a switch or a router to another server within a rack.

Micro and Macro Channel Liquid Cooling

Rogers now provides curamik CoolPower and CoolPower Plus as well as the curamik CoolPerformance and CoolPerformance Plus. The liquid coolers feature either a micro or macro channel structure made of thin copper foils that are put together into a hermetically tight block using Rogers’ curamik bonding process. The specific channel structure determines the thermal resistance, pressure drop and flow rate. The coolant usually enters and exits through openings connected with O-rings or screw fittings.

Ideal for high power applications, the curamik CoolPerformance coolers are high performance copper coolers for laser diode cooling. curamik CoolPerformance Plus coolers are high performance isolated copper coolers that contain an AlN isolation layer on top and bottom.

Thermal Tape Offers Low Thermal Resistance

DuPont Temprion AT adhesive thermal tapes deliver grease-like wettability at low application pressures, providing the freedom to assemble devices without introducing excess stress to a system’s complex circuitry.

The highly conformable pressure-sensitive adhesive tapes achieve low thermal impedance at only 20 psi of pressure to offer best-in-class thermal performance, easier package assembly, reduced device failure and higher system performance. Thermal conductivity is 0.7 W/m·K.

Use of Temprion AT thermal tapes eliminates the need for mechanical fasteners when assembling electronic packages. Applications include heat sink attachment for CPUs and GPUs, LED bonding, and assembly of flat panel displays.

Peltier Coolers Keep Machine Vision Systems Cool

The HiTemp ET Series Peltier thermoelectric module from Laird Thermal Systems is designed to keep the sensors in machine vision systems cool and operating at peak performance. Solid-state thermoelectric coolers can reduce the sensor’s temperature to meet proper design specifications.

A standard single-stage Peltier cooler can achieve temperature differentials of up to 70°C, while a multi-stage Peltier module can achieve much higher ΔTs. Thermoelectric modules are integrated directly into the sensor assembly and typically require a heat sink or other heat exchanger to dissipate heat into the surrounding environment.

Supporting applications operating in temperatures ranging from 80 to 150°C, the single-stage HiTemp ET Series offers a cooling capacity of more than 300 watts in a compact form factor. The HiTemp ET Series includes over 50 models with a wide variety of heat pumping capacities, form factors and input voltages.

InRow Data Center Cooling Solution 

Schneider Electric has expanded its EcoStruxur Ready cooling portfolio with a 30kW InRow DX solution. Available in a 300mm rack format, this data center cooling solution offers industry leading efficiency and addresses the increasing demand for higher density cooling in the data center.

The trend toward modernization and consolidation of data centers is driving the need for a cooling solution that provides more cooling capacity in a smaller footprint and flexible capacity to adapt to the actual data center load. The 30kW InRow DX is ideal for data centers that are being modernized or retrofitted, or anywhere IT space is at a premium.

Due to its powerfully compact size and energy efficient design, the InRow DX is the most versatile and predictable cooling system for next generation small and medium data centers and an optimal choice for edge and enterprise environments. The 30kW InRow system can provide 30% improved efficiency, reducing operating expenses and improving PUE (power usage effectiveness).

For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit or contact ATS at 781.769.2800 or To register for Qpedia and to get access to its archives, visit

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 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.



For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit or contact ATS at 781.769.2800 or To register for Qpedia and to get access to its archives, visit

Thermal Performance of Heat Sinks with Heat Pipes or Vapor Chambers for Servers

Most blade servers for data and telecommunication systems use air to cool the high-power chips inside. As the power level of these chips keep increasing, the pressure is on thermal engineers to design ever higher performance air-cooled heat sinks. In recent years, advancements in manufacturing of thinner heat pipes and vapor chambers have enabled engineers to integrate the heat pipes and vapor chambers into the blade server heat sinks.

A heat pipe is a device with high thermal conductance that can transport large amounts of heat with a small temperature difference between its hot and cold ends. The idea of a heat pipe was first proposed by Gaugler [1]. However, only after its invention by Grover [2, 3] in the early 1960s, were the remarkable properties of heat pipes realized by scientists and engineers. It is now widely used to transport heat from one location to another location or to smooth the temperature distribution on a solid surface.

A heat pipe is a self-driven two-phase heat transfer device. A schematic view of a heat pipe is shown in Figure 1. At the hot section (evaporator), the liquid evaporates and turns to vapor. The vapor flows to the cold section (condenser) and liquefies there. The liquid is driven back from the cold section to the hot section by a capillary force induced by the wick structure. By using boiling and condensation, the heat pipes can transfer and spread the heat from one side to another side with a minimum temperature gradient.

Figure 1. Typical heat pipe. [4]

Vapor chambers are flat heat pipes with very high thermal conductance. They have flat surfaces on the top and bottom sides.  See Figure 2, which can be easily attached to a heat source and a heat sink.

Figure 2. Vapor chamber. [5]

Just like heat pipes, vapor chambers use both boiling and condensation to maximize their heat transfer ability. A vapor chamber generally has a solid metal enclosure with a wick structure lining the inside walls. The inside of the enclosure is saturated with a working fluid at reduced pressure. As heat is applied at one side of the vapor chamber, the fluid at locations close to the heat source reaches its boiling temperature and vaporizes. The vapor then travels to the other side of the vapor chamber and condenses into liquid. The condensed fluid returns to the hot side via the gravity or capillary action, ready to vaporize again and repeat the cycle.

In electronics cooling, heat pipes are generally used to move the heat from electronics to heat dissipation devices. For example, in a desktop computer, multiple heat pipes are used to transfer heat from a CPU to an array of cooling fins, which dissipate the heat to ambient environment through convection. Vapor chambers are generally used to spread heat from a small size device to a larger size heat sink, as it is shown in Figure 2. If used in server heat sinks, the heat pipes and vapor chambers are both used to spreading the heat due to the low profile and large footprint of the heat sinks.

Compared to copper heat spreaders, heat pipes and vapor chambers have the following merits.

First, they have a much higher effective thermal conductivity. The pure copper has a thermal conductivity of 401 W/m°C and the best conductive material of diamond has a thermal conductivity of 1000-2000 W/m°C. The effective thermal conductivity of a well-designed heat pipe and vapor chamber can exceed 5000 W/m°C, which is an order of magnitude higher than that of pure copper. Second, the density of the heat pipe and vapor chamber is much lower than that of copper. Due to its hollow structure, the heat spreaders made by vapor chambers are much lighter than those made of copper. These properties make them the ideal candidate for high heat flux and weight sensitive heat spreading applications.

Dynatron Corporation is an electronic cooling provider specializing in heat sink for servers. This article compares the thermal performance of its server heat sinks, some of which have integrated vapor chambers. Figure 3 shows the photos of two Dynatron 1U passive server heat sinks for Intel’s Sandy Bridge EP/EX Processors. The R12 is made of pure copper with skived fins. The R19 has a vapor chamber base and stacked copper fins. The heat sink specification is listed in Table 1. The R19 is 150g lighter than the R12.

Figure 3. Dynatron passive heat sinks R12 (left) and R19 (right). [6]
Table 1. Dynatron passive heat sink specification.

Figures 4 and 5 show the thermal performance of R12 and R19 at different flow rates. At 10CFM, both heat sinks have a thermal resistance of 0.298ºC/W. When the flow rate increases to 20CFM, the R19’s thermal resistance is 0.218ºC/W, which is 0.020ºC/W lower than that of R12.

Figure 4. Dynatron R12 heat sink performance. [6]
Figure 5. Dynatron R19 heat sink performance. [6]

Figure 6 shows the photos of two Dynatron 1U active server heat sinks for Intel’s Sandy Bridge EP/EX Processors. The R18 is made of copper with skived fins. The R16 has vapor chamber base and stacked copper fins. Both heat sinks use same blower. The heat sink specification is listed in Table 2. The R16 is 90g lighter than the R18.

Figure 6. Dynatron active heat sinks R18 (left) and R16 (right). [6]
Table 2. Dynatron active heat sink specification. [6]

Figures 7 and 8 show the thermal performance of R18 and R16 at different blower speeds. At 3000RPM, the R18 and R16 heat sinks have thermal resistance of 0.437ºC/W and 0.393ºC/W, respectively. When the blower speed increases to 6000RPM, the R18’s thermal resistance is 0.268ºC/W and the R16’s thermal resistance is 0.241ºC/W. The R16 is constantly able to outperform the R18 at different blower speeds and its thermal resistance is 10% lower than R18.

Figure 7. Dynatron R18 heat sink performance. [6]
Figure 8. Dynatron R16 heat sink performance. [6]

The comparison of the Dynatron heat sinks shows that heat sinks with vapor chambers have a slight thermal edge vis-a-vis its copper counterparts even though they are light. This is true for both passive and active heat sinks.

Glover et al., for Cisco, have tested different heat sinks either with embedded heat pipes or vapor chambers for their servers and published their findings [7]. They tested five different heat sinks from different vendors, who utilized different manufacturing technologies to fabricate the heat sinks. The five heat sinks are similar in size: 152.4 x 101.6 x 12.7mm. Table 3 summarizes the physical attributes of these five heat sinks.

Table 3. Cisco tested heat sink specification. [7]

Figure 9-11 shows the three vapor chamber heat sinks with different vapor chamber structures and fin designs. Heat sink A-1 is an extruded aluminum heat sink with a vapor chamber strip. The 40 mm wide vapor chamber strip is embedded in the center of the base. It is the lightest one among five tested heat sink. Heat sink B-1 and C-1 have full base size vapor chamber and aluminum zipper fins.

Figure 9. Heat sink with vapor chamber A-1. [7]
Figure 10. Heat sink with vapor chamber B-1. [7]
Figure 11. Heat sink with vapor chamber C-1. [7]

Figures 12-13 show the two heat sinks with embedded heat pipes. Heat sink C-2 has heat pipes embedded inside its aluminum base. It uses zipper fins and has a copper slug in the middle of the base. Heat sink D-1 has three flat heat pipes embedded in its base. It has a copper plate as base.

Figure 12. Heat sink with heat pipes C-2. [7]
Figure 13. Heat sink with heat pipes D-1. [7]

Glover et al. tested the five heat sinks at different mounting orientation and air velocity. Table 4 presents the summary results of the heat sinks at 3m/s approach air velocity. The tested heat sinks were mounted horizontally with heater sources underneath the heat sink bases.

Table 4. Heat Sink Performance at 3 m/s with horizontal mounting position and bottom heating. [7]

The C-1 heat sink has the lowest thermal resistance; thus, its values are used as the benchmark for other heat sinks. The performance of heat sinks is purely design dependent. For vapor chamber heat sinks, the thermal resistance value varies from 0.19 to 0.23°C/W for 30 W of power. For heat sinks with heat pipes, the C-2 heat sink has a thermal resistance of 0.23°C/W, which matched with that of A-1 and B-1.

The D-1 heat sink has the highest thermal resistance, which is the result of inferior design and manufacture. However, the D-1 heat sink still has relatively low thermal resistance when it is compared to a regular heat sink without a heat pipe and vapor chamber.

Figure 14 shows the thermal resistance of the five heat sinks for 60W of input power at different air velocities. The C-1 heat sink performs best for all velocities and the D-1 heat sink’s performance is the worst.

Figure 14. Heat sink thermal resistance at 60 W. [7]

The pressure drop across the heat sink at different air velocities was also measured and the results were plotted in Figure 15. The B-1, C-1 and C-2 heat sinks have similar fin structures. Therefore, their pressure drop is similar, too. The pressure drop of the A-1 and D-1 heat sinks are similar and higher than the other heat sinks. This is because the A-1 heat sink has thicker fins and the D-1 heat sink has a thicker base.

Figure 15. Heat sink pressure drop. [6]

Because the heat pipes and vapor chambers use capillary force to drive liquid back from the condensation section to the evaporation section, their thermal performance is prone to orientation variation. Glover et al. also investigated the effects of the mounting orientation on the performance of the five heat sinks. They found the effect of the orientation is design dependent and is the result of both the wick structure and the entire heat sink assembly construct.

The heat sink specification from Dynatron Corporation and the test results from Cisco, show that the server heat sinks with embedded heat pipes or vapor chamber have a better thermal performance than their copper counterparts. The heat sinks with embedded heat pipes or vapor chamber are also lighter than the pure copper heat sinks, which make them more suitable for applications which are weight sensitive. If the cost of such heat sinks is justified, they are definitely good candidates for server cooling applications.


  1. Gaugler, R. S., US Patent 2350348, Appl. 21 Dec, 1942. Published 6 Jun. 1944.
  2. Grover, G. m., US Patent 3229759. Filed 1963.
  3. Grover, G. M., Cotter, T. P., and Erickson, G. F., “Structure of Very High Thermal Conductance.” J. App. Phys., Vol. 35, P. 1990, 1964.
  6. http://
  7. Glover, G., Chen, Y., Luo, A., and Chu, H., “Thin Vapor Chamber Heat Sink and Embedded Heat Pipe Heat Sink Performance Evaluations,” 25th IEEE SEMI-THERM Symposium, San Jose, CA, USA, 2009.

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June Webinar on Temperature Measurement in Electronics Systems

Advanced Thermal Solutions, Inc. (ATS) is hosting a series of monthly, online webinars covering different aspects of the thermal management of electronics. This month’s webinar will be held on Thursday, June 20th from 2-3 p.m. ET and will cover how to perform and understand temperature measurement in electronics systems. Learn more and register at