Tag Archives: Norman Quesnel

Industry Developments: Cooling QSFP Optical Transceivers

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

Rapid advancements in fiber optic technology have increased transfer rates from 10GbE to 40/100GbE within data centers. With the emergence of 100GbE technologies, the creation of data center network architectures free from bandwidth constraints has been made possible. The major enabler of this performance increase is the QSFP optical transceiver.

QSFP is the Quad (4-channel) Small Form-Factor Pluggable optical transceiver standard. A QSFP transceiver interfaces a network device, e.g. switch, router, media converter, to a fiber optic or copper cable connection as part of a Fast Ethernet LAN.

The QSFP design became an industry standard via the Small Form Factor Committee in 2009. Since then, the format has steadily evolved to enable higher data rates. Today, the QSFP MSA (multi-source agreement) specification supports Ethernet, Fibre Channel (FC), InfiniBand and SONET/SDH standards with different data rate options.

QSFP

Fig. 1. The Small QSFP Form Factor Allows More Connectors and Bandwidth than Other Fiber Optic Transceiver Formats. Note the Cooling Fins on Each Receiver Device. [1]

Thermal Issues

The small QSFP form factor has significantly increased the number of ports per package. The increased density of transceivers can lead to heat issues. The optical modules can get hot due to their use of lasers to transmit data. Even though the popular QSFP28 provides lower power dissipation than earlier transceivers – abut 3.5W, the QSFP28 factor has also allowed a significant increase in port density.

Newer microQSFPs can dissipate even more heat. microQSFP interconnects fit more ports (up to 72) on a standard line card, saving significant design space.

Fig 2. Air Gap Locations Shown in Thermal Specifications Feature on QSFP. Top: QSFP at the Inside Edge of a Cage, Bottom: QSFP Section Showing Typical Internal Layout. [2]

The performance and longevity of the transceiver lasers depend on the ambient temperature they operate in and the thermal characteristics of the packaging of these devices. The typical thermal management approach combines heat dissipating fins, e.g. heat sinks, and directed airflow.

Fig 3. Test set-up of different heat sink designs on QSFP28 connector cages. (Advanced Thermal Solutions, Inc.)

Recently, Advanced Thermal Solutions, Inc. (ATS) tested a variety of pin and fin-style heat sinks for their comparative cooling performance on a standard QSFP connector cage. For this setup, an even amount of heat was provided to each connector site via a heater block. Individual thermocouples measured the heat flux resulting with the different heat sink types.

A main goal of this test was how each of four heat sinks would perform while relying on airflow incoming from just one side. By the time it reached the fourth heat sink would the airflow provide enough conduction for adequate cooling? An image from this series of tests is below in Figure 4.

Fig. 4. Test Setup to measure cooling performance of individual heat sinks on a QSFP connector cage when airflow is from one side only. (Advanced Thermal Solutions, Inc.)

The tests results showed that the denser the heat sink pins or fins on the sink closest to the incoming air, the hotter the farthest away QSFP will be. Thus, the best solution used heat sinks whose pin/fin layouts were optimized to work in the actual airflow reaching them.

This meant more open layouts closer to the air source, allowing more air to reach denser pin/fin sinks farther from the air. The non-homogeneous heat sinks allowed for a low, uniform temperature across the QSFP for the most effective function of the QSFPs’ lasers.

microQSFPs

Cooling solutions are different between QSFP28 designs and microQSFP installations. QSFP28 transceiver cooling is typically provided at multiple connector sites. microQSFP modules, e.g. from TE Connectivity, have an integrated heat sink in the individual optical module. Used with connection cages that are optimized for airflow, their heat is controlled in high density applications.

Fig. 5. Integrated Module Thermal Solution (Fins) on microQSFPs Provides Better Thermal Performance and Uses Less Energy for Air Cooling. [3]

Fig. 6. A Video Demo from TE Connectivity Shows 72 Ports of microQSFP Transceivers Units Running at 5W Each and All Kept Under 55°C Temperature Using 82 CFM Airflow. [4]

Finally, another factor affecting cooling performance is surface finish and flatness. Designers can reduce thermal spreading losses by keeping the heat sources close to the thermal interface area and by increasing the thermal conductivity of the case materials.

For QSFP, the size of the cage hole for heat sink contact given in the multi-source agreement (MSA) can be increased giving a reduction in the thermal interface resistance and therefore module temperature.

References:
1. FMAD IO, http://fmad.io/images/blog/20160612-100g-connectors.png
2. https://arkansashq.wordpress.com/2016/10/11/pluggable-optics-modules-thermal-specifications-part-2/
3. microQSFP, http://www.microqsfp.com/
4. TE Connectivity, https://www.youtube.com/watch?v=k_qNj-yAKz4

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

Industry Developments: Heat Exchangers for Electronics Cooling

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

(This article will be featured in an upcoming 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. To read other stories from Norman Quesnel, visit https://www.qats.com/cms/?s=norman+quesnel.)

Heat exchangers are thermal management tools that are widely used across a variety of industries. Their basic function is to remove heat from designated locations by transferring it into a fluid. Inside the heat exchanger, the heat from this fluid passes to a second fluid without the fluids mixing or coming into direct contact. The original fluid, now cooled, returns to the assigned area to begin the heat transfer process again.

The fluids referred to above can be gases (e.g. air), or liquids (e.g. water or dielectric fluids), and they don’t have to be symmetrical. Therefore, heat exchangers can be air-to-air, liquid-to-air, or liquid-to-liquid. Typically, fans and/or pumps are used to keep these heat transfer medium in motion and heat pipes may be added to increase heat transfer capabilities.

Figure 1 shows a basic heat exchanger schematic. A hot fluid (red) flows through a container filled with a cold fluid (blue) but the two fluids are not in direct contact.

Heat Exchanger

Figure 1. In a Simple Heat Exchanger Heat Transfers from the Hot (Red) Fluid to the Cold (Blue) Fluid, and the Cooler After Fluid Re-Circulates to Retrieve More Heat. [1]

One example of a common heat exchanger is the internal combustion engine under the hood of most cars. A fluid (in this case, liquid coolant) circulates through radiator coils while another fluid (air) flows past these coils. The air flow lowers the liquid coolant’s temperature and heats the incoming air.

Applied to electronics enclosures, heat exchangers draw heated air from a cabinet, cool it, and then return the cooled air to the cabinet. These heat exchangers should be designed to provide adequate cooling for expected worst case conditions. Typically, those conditions occur when the ambient is the highest and when electrical loads through the enclosure are very high. Under typical conditions, heat exchangers can cool cabinet interiors to within 5°F above the ambient air temperature outside the enclosure.

Air-to-Air

Air-to-air heat exchangers have no loops, liquids or pumps. Their heat dissipation capabilities are moderate. Common applications are in indoor or outdoor telecommunications cabinetry or in manufacturing facilities that don’t have a lot of dust or debris.

Air-to-air heat exchangers provide moderate to good cooling performance. They don’t allow outside air to enter or mix with the air inside the enclosure. This protects the enclosure’s contents from possible contamination by dirt or dust, which could damage sensitive electronics and electrical devices and cause malfunctions.

An example of higher performance, air-to-air heat exchangers is the Aavid Thermacore HX series. These heat exchangers feature rows of heat pipes that add effective, two-phase heat absorbing properties when moving hot air away from a cooling area. The liquid inside the heat pipes turns to vapor. This transition occurs inside a hot cabinet. (See Figure 2)

The vapor travels to the other end of the heat pipe, which is outside the cabinet. Here it is cooled by a fan, transitions back to liquid form, and cycles back inside the cabinet environment.

Heat Exchangers

Figure 2. An Air-to-Air Heat Exchanger with Heat Pipes Extending Inside (top) and Outside (bottom) a Cabinet. Internal Heat is Transferred Outside the Enclosure. (Aavid Themacore) [1]

Other air-to-air heat exchangers feature impingement cooling functionality that can provide better performance than using heat pipes. Aavid Thermacore’s HXi Impingement core technology uses a folded fin core that separates the enclosure inside and outside. A set of inside fans draws in the hotter, inside air and blows it toward the fin core. This inside impingement efficiently transfers the heat to the fin core. Similarly, a set of outside fans draws in the cooler, ambient air and blows it toward the outer side of the fin core removing the waste heat. See Figure 3 below.

Heat Exchangers

Figure 3. Air-to-Air Heat Exchangers with Double-Sided Impingement Cooling Technology Can Move Twice the Heat Load of Conventional Exchangers. (Aavid Themacore) [3]

Liquid-to-Air

In some electronic cabinets, high power components can’t be cooled by circulating air alone or the external ambient air temperature is not cool enough to allow an air-to-air heat exchanger to solve the problem unaided. In these applications, liquid-to-air heat exchangers provide additional cooling to maintain proper cabinet temperatures.

For example, in a situation where heat is collected through a liquid-cooled cold plate attached directly to high power components. Even with the cold plate, the ambient air external to the cabinet is not cool enough to maintain the internal cabinet temperature at an acceptable or required level. Here, a liquid coolant in an active liquid-to-air heat exchanger can be used to cool the enclosure.

Heat Exchangers

Figure 4. Tube-to-Fin, Liquid-to-Air Heat Exchangers Provide High-Performance Thermal Transfer. [4] (Advanced Thermal Solutions, Inc.)

Advanced Thermal Solutions, Inc. (ATS) tube-to-fin, liquid-to-air heat exchangers have the industry’s highest density of fins. This maximizes heat transfer from liquid to air, allowing the liquid to be cooled to lower temperatures than other exchangers can achieve. All tubes and fins are made of copper and stainless steel to accommodate a wide choice of fluids.

Available with or without fans, ATS heat exchangers are available in a range of sizes and heat transfer capacities up to 250W per 1°C difference between inlet liquid and inlet air temperatures. They can be used in a wide variety of automotive, industrial, HVAC, electronics and medical applications. [4]

Heat Exchanger

Figure 5. Small, Light-Weight Liquid-to-Liquid Heat Exchanger Provides Efficient Cooling Performance. [5]

Lytron’s liquid-to-liquid heat exchangers are only 10-20% the size and weight of conventional shell-and-tube designs. Their internal counter-flow design features stainless steel sheets stamped with a herringbone pattern of grooves, stacked in alternating directions to form separate flow channels for the two liquid streams. This efficient design allows 90% of the material to be used for heat transfer. Copper-brazed and nickel-brazed versions provide compatibility with a wide range of fluids. [5]

Nanofluids

The development of nanomaterials has made it possible to structure a new type of heat transfer fluid formed by suspending nanoparticles (particles with a diameter lower than 100nm). A mixture of nanoparticles suspended in a base liquid is called a nanofluid. The choice of base fluid depends on the heat transfer properties required of the nanofluid. Water is widely used as the base fluid. Experimental data indicates that particle size, volume fraction and properties of the nanoparticles influence the heat transfer characteristics of nanofluids. [5]

When compared to conventional liquids, nanofluids have many advantages such as higher thermal conductivity, better flow, and the pressure drop induced is very small. They can also prevent sedimentation and provide higher surface area. From various research, it has been found that adding even very small amounts of nanoparticles to the base fluid can significantly enhance thermal conductivity.

Heat Exchangers

Figure 6. 3D Design of Curved Tube Heat Exchanger. Increased Turbulence and Velocity Increases Heat Transfer Rate. [6]

A recent paper by Fredric et al. proposes a theoretical heat exchanger with curved tubes and with nanofluids as the coolant. Nanofluids in place of regular water provide improved thermal conductivity due to the increased surface area. The heat transfer rate is further improved using curved tubes in place of straight tubes because the used of curved tubes increases the turbulence and fluid velocity, which helps increase the heat transfer rate. [6]

References
1. Advanced Thermal Solutions, Inc., https://www.qats.com/Products/Liquid-Cooling/Heat-Exchangers.
2. Aavid Thermacore, http://www.thermacore.com/documents/system-level-cooling-products.pdf.
3. Aavid Thermacore, http://www.thermacore.com/products/air-to-air-heat-exchangers.aspx.
4. Advanced Thermal Solutions, https://www.qats.com/Products/Liquid-Cooling/Heat-Exchangers.
5. Kannan, S., Vekatamuni, T. and Vijayasarathi, P., “Enhancement of Heat Transfer Rate in Heat Exchanger Using Nanofluids,” Intl Journal of Research, September 2014.
6. Fredric, F., Afzal, M. and Sikkandar, M., “A Review on Shell & Tube Heat Exchanger Using Nanofluids for Enhancement of Thermal Conductivity,” Intl. Journal of Innovative Research in Science, Engineering and Technology, March 2017.

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

Industry Developments in District Cooling Systems

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

(This article will be featured in an upcoming 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. To read other stories from Norman Quesnel, visit https://www.qats.com/cms/?s=norman+quesnel.)

District cooling is the centralized production and delivery of cooling energy to collective regions of office, public or domestic structures. In a typical district cooling scheme, a central plant chills water from a contained reservoir or taken from an ocean or lake. The chilled water is delivered via underground, insulated pipelines to select buildings in a district. The buildings contain pumps and tubing systems that circulate the cold water within the living areas.

Air is forced past the circulating cold water to produce an air conditioned environment. The resulting warmed water in the tubes is returned to the central plant for re-chilling and recirculating.

District cooling can use either regular water or seawater and can be powered by electricity or natural gas. The output of one district cooling plant is enough to meet the cooling-energy demands of dozens of buildings. [1]

Nowhere is advanced district cooling being developed more than in the Middle East, particularly in its wealthier – and hotter – countries like those in the Gulf Cooperation Council (GCC): Saudi Arabia, Kuwait, United Arab Emirates (UAE), Qatar, Bahrain and Oman. Air conditioning is responsible for about 70 percent of the GCC’s electricity demand during peak summer months.

District Cooling

Figure 1. CAD Image of District Cooling in a High-Rise Building in Lusail City, an Urban Development Planned for Qatar. [2]

One district cooling example is Qatar’s very smart Lusail City. Still largely in planning, Lusail will use a state-of-the-art system to provide cool environments in its modern business and residential buildings. In typical fashion, the Lusail system will use chilled water in pipes feeding to different localities via an extensive system of underground tunnels and local substations. [2]

High Cooling Performance

In many ways, district cooling is a superior alternative to conventional, localized air conditioning. It helps reduce costs and energy consumption for both customers and governments alike, while also protecting the environment by cutting carbon dioxide emissions.

District Cooling

Figure 2. District Cooling Systems can Store 30% of Potential Cooling Output by Holding Water in Reserve for Seasonal Requirements. [3]

Some of the advantages district cooling has over traditional air conditioning includes 50 percent less energy consumption with better accommodation of peak cooling power demands. There are substantially lower maintenance costs than for individual, localized units. District cooling’s equipment has, on average, a 30-year working life, just about as long as conventional urban air conditioning systems.

District cooling systems reduce CO2 emissions because of their lower energy consumption. The centralized systems also free up useable space in individual buildings, including rooftops and basements where local cooling systems were formerly installed. [3]

District Cooling

Figure 3. District Cooling Layout for King Abdullah Financial District (KAFD) Under Construction Near Riyadh, Saudi Arabia. Total Capacity is 100,000 Tons of Refrigeration. [4]

District cooling is measured in tons of refrigeration, TRs, equivalent to 12,000 BTUs per hour. A refrigeration ton is the unit of measure for the amount of heat removed. It is defined as the heat absorbed by one ton (2,000 pounds) of ice causing it to melt completely by the end of one day (24 hours). In Qatar and Saudi Arabia, the district cooling systems being developed will contribute a combined 4.5 million tons of refrigeration.

District Cooling

Figure 4. District Cooling at the Nation Towers Area of Abu Dhabi is Managed by Tabreed, Which has 71 District Cooling Plants Throughout the Gulf Cooperation Council, GCC. [5]

Nation Towers is the site of two skyscrapers near the southern end of the ocean-bordering Corniche in Abu Dhabi, the capital of the UAE. The towers, 65 and 52 floors tall respectively, are joined by a sky bridge and together offer nearly 300,000 m2 of usable space.

The towers and the surrounding structures are air conditioned by a district cooling plant managed by Tabreed, the largest name in district cooling in the GCC. In 2015, per Tabreed, the company’s UAE-based district cooling systems reduced the amount of energy used in air conditioning by 1.3 billion kilowatt hours – the equivalent use of 44,000 UAE homes. [6]

Northeast from Abu Dhabi, the UAE city of Dubai is home to the sprawling WAFI Mall. The site uses Siemens Demand Flow technology to optimize the chilled water system that keeps its stores and restaurants at comfortable temperatures. Siemens Demand Flow technology uses specialized algorithms to optimize the entire chilled water system of a cooling plant, delivering energy savings of between 15 and 30 percent.

By simplifying operations, increasing the cooling capacity and improving efficiency, the system is able to reduce flow in periods of lesser demand, lowering operation and maintenance costs and significantly lowering energy use. [7]

But the Middle East is not the only part of the world employing district cooling. In another warm country, India, a new business district is being constructed on nearly 900 acres in the state of Gujarat. This is the Gujarat International Finance Tec-City, whose district cooling will provide a total cooling capacity of 1,800,000 TR. [8]

In Europe, Copenhagen is home to a successful district cooling operation. The city may not be thought of as in much need of air conditioning; summer high temperatures rarely exceed the mid-70s Fahrenheit. But even in Denmark, there is a need for indoor cooling inside buildings with large server rooms or where many people work or shop. The northern city already had a district heating system and harnessed much of that infrastructure to add cooling.

District Cooling

Figure 5. Copenhagen’s District Cooling System Reduces Carbon Emissions by Nearly 70% and Electricity Consumption by 80% Compared to Conventional Cooling. [5] (Pictured: Heat pipes running under Copenhagen/Wikimedia Commons)

At times Copenhagen’s ocean water is so cold it doesn’t need to be chilled, which saves energy. The district cooling is targeted for co-located buildings (department stores, commercial buildings, hotels, and facilities with data centers) with cooling demands of 150 kilowatts (kW) or more. [9]

And in the U.S., Thermal Chicago provides the country’s biggest district cooling system. It includes five interconnected plants providing cooling to more than 100 buildings in the Windy City. During peak time of air conditioner use, the Thermal Chicago cooling system has reduced energy demand by more than 30 megawatts.

The facility’s also uses a different water-chilling technology that includes an ice-based thermal storage tank for faster cooling and return of chilled water to the infrastructure needing cooling. A YouTube video explains how Thermal Chicago water cooling is set up. [10]

District Cooling

Figure 6. Ice-based Cooling Section Within the Thermal Chicago District Cooling System, from YouTube Video. [10]

Recapping the basic steps of district cooling:

• A central plant chills water.
• A primary water circuit then distributes the chilled water to buildings through an underground insulated pipes network.
• A secondary water circuit in the customers’ building circulates the cold water.
• Air is then forced past the cold water tubing to produce an A/C environment.
• The warmer water of the primary circuit is returned to the central plant to be re-chilled and recycled.

District cooling is not a new technology, or even a new concept. Centralized production and distribution of temperature control has been in commercial use since the 19th century, mainly for heating purposes.

Today, for efficiency and environmental reasons – including rising global temperatures – district cooling is seeing a renaissance by being designed into many of the smarter cities being built around the world.

References
1. Tabreed, https://www.tabreed.ae/en/district-cooling/district-cooling-overview.aspx
2. Lusail City, http://www.lusail.com
3. CELCIUS Smart Cities, http://celsiuscity.eu/
4. Saudi Tabreed, http://www.fleminggulf.com/files/doc/DBUT09/Abdul_Jalil_Bakhruji.pdf
5. Tabreed, https://www.tabreed.ae/en/district-cooling/our-district-cooling-plants.aspx
6. The National UAE, http://www.thenational.ae/uae/environment/tabreed-reduces-carbon-emissions
7. Siemens, http://www.middleeast.siemens.com/me/en/news_events/news/news-2016/siemens-smart-building-tech-can-cut-gccs-cooling-bill-by-40.htm
8. Gujarat International Finance Tec-City, http://giftgujarat.in/district-cooling-system
9. Forbes, https://www.forbes.com/sites/justingerdes/2012/10/24/copenhagens-seawater-cooling-delivers-energy-and-carbon-savings/#1f8d40d74245
10. Thermal Chicago video, https://www.youtube.com/watch?v=ziEbY0oLf-o

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

Industry Developments for Cooling Overclocked CPUs

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

(This article will be featured in an upcoming 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. To read other stories from Norman Quesnel, visit https://www.qats.com/cms/?s=norman+quesnel.)

Almost as long as personal computers have been around, users have been making modifications “under the hood” to make them run faster. A large segment of these users are overclockers, who make adjustments to increase the clock speeds (the speed at which processors execute instructions) of their CPUs and GPUs.

Many PC gamers get into overclocking (OC) to make their programs run faster. Gamecrate.com, a gamer site, defines overclocking as the practice of forcing a specific piece of hardware to operate at a speed above and beyond the default manufactured rating. [1]

To overclock a CPU is to set its clock multiplier higher so that the processor speeds up. For example, overclocking an Intel Core i7 CPU means to push its rated clock speed higher than the 2.80 GHz that it runs at “out of the box.” When performed correctly, overclocking can safely boost a CPU’s performance by 20 percent or more. This will let other processes on a computer run faster, too.

Cooling Overclocked CPUs

Fig. 1. An Intel Core i5-469k Processor Can Be Overclocked to Run 0.5-0.9 GHz over Its Base Frequency. Air Cooling is Provided by a Hyper D92 from Cooler Master.[2]

To serve the global overclockers market, some chip makers keep the door open to overclocking by allowing access to their multipliers. They do this with a variety of “unlocked” processors. Intel provides many unlocked versions of their processors, as denoted with a ‘k’ at the end of their model number.

For example, the Skylake Core i7-6700k and Haswell-E Core i7-5820k are made with unlocked clock multipliers. In fact, Intel targets overclockers with marketing campaigns and support services.

Fig. 2. Intel Actively Targets Overclockers with Its Unlocked Processors.[3]

Besides gaming, overclocking can improve performance for applications such as 3-D imaging or high-end video editing. For GPUs, faster speeds will achieve higher frames per second for a smoother, faster video experience. Overclocking can even save money, if a lower cost processor can be overclocked to perform like a higher end CPU.[4]

For many gamers, overclocking enhances their enjoyment by giving more control over their system and breaking the rules set by CPU manufacturers. One overclocker on Gamecrate.com said, “Primarily, I like to do it because it’s fun. On a more practical note it’s a great way to breathe some life into an old build, or to take a new build and supercharge it to the next level.”[1]

Heat Issues from Overclocking

Overclocking a processor typically means increasing voltage as well. Thus, the performance boost from overclocking usually comes with added component heat that needs to be controlled. Basically, the more voltage added to components, the more heat they are going to produce. There are many tutorials on overclocking and most of these resources stress that it’s essential to manage a component’s increased heat.[5]

Programs are available that monitor the temperature of a processor before and after overclocking it. These programs work with the DTS, digital thermal sensors that most processor manufacturers include inside their component packages. One such program is Core Temp, which can be used with both Intel and AMD cores. Some component OEMs also offer their own software to monitor temperatures in their processors.[6]

Fig. 3. The Core Temp Program Can Display Temperatures of Individual Cores in a System.[6]

Typically, an overclocker will benchmark a CPU or other component to measure how hot it runs at 100 percent. Advanced users can manually do the overclocking by changing the CPU ratio, or multiplier, for all cores to the target number. The multiplier works with the core’s BCLK frequency (usually 100) to create the final GHz number.

Tools like the freeware program Prime95 provide stability testing features, like the “Torture Test,” to see how the sped up chip performs at a higher load. These programs work with the system’s BIOS and typically use the motherboard to automatically test a range of overclocked profiles, e.g. from 4.0-4.8 GHz. From here, an overclocker may test increasing voltages, e.g. incrementally adding 0.01 – 0.1 V while monitoring chip stability.

An overclocked component’s final test is whether it remains stable over time. This ongoing stability will mainly be influenced by its excess heat. For many overclocked processors, a robust fan-cooled heat sink in place of the stock fan is essential. For others, only liquid cooling will resolve excess heat issues.

Fan Cooling

The advantage of using air coolers is no worry about leaking, which may lead to component or system damage. With the air cooled heat sinks, the bigger and faster the fan (CFM), the better, and there are a multitude of fan-sink cooling solutions that gaming PCs can accommodate.

In reality, higher performance fan-cooled sinks typically also employ liquid. It is used inside heat pipes that more efficiently convey heat from the processor into the sink’s fan cooled fin field.

Fig. 4. The Top-Rated Hyper 212 EVO CPU Air Cooler from Cooler Master Has Four Heat Pipes Transferring Heat to Aluminum Fins.[7]

Air cooled heat sinks for overclockers cost well under $50 and are available from many sources. They’re often bundled with overclock-ready processors at discounted prices.

A greater issue with air cooling can be the fan noise. A high performance fan must spin very quickly to deal with heavy system workloads. This can create an unpleasant mixture of whirs, purrs and growls. Many of the gaming desktops generate 50-80 decibels of noise at load. Though most fans are quieter, pushing out 25-80 CFM, they are louder than most standard PC processor fans.[8]

Liquid Cooling

Liquid cooling has become more common because of its enhanced thermal performance, which allows higher levels of overclocking. Prices are definitely higher than air-cooled heat sinks, but liquid systems offer enthusiasts a more intricate, quieter, and elegant thermal solution with definite eye-appeal.

From the performance standpoint, liquids (mainly water in these systems) provide better thermal conductivity than air. They can move more thermal energy from a heat source on a volume-to-volume basis.

Fig. 5. The Top-Rated Nepton 280 Liquid CPU Cooler Has a Fast Pump Flow and a Large Radiator Cooled with Dual Fans that Reach 122 CFM Airflow.[9]

A typical liquid cooling system features a water block that fits over the overclocked CPU, a large surface area, a fan-cooled heat exchanger (radiator), a pump, and a series of tubes connecting all elements. One tube carries hot fluid out from the water block, the other returns it once it is cooled by the radiator. Some liquid cooling systems can also be used on multiple processors, e.g. a CPU and a gaming chipset.

While there are more components to a liquid cooling system, there are also major advantages. For one, the water block is usually much smaller and lower-profile than an attached, high-performance air cooler. Also, the tubing set up allows the heat exchanger and pump to be installed in different locations, including outside the PC enclosure. An example is the Sub-Zero Liquid Chilled System from Digital Storm. It unlocks overclocks of Intel’s i7-980X CPU up to 4.6 GHz while idling the processor below 0°C.[10]

Fig. 6. Digital Storm’s Cryo-TEC System Places an Overclocked CPU in Direct Contact with Thermo-electric Cold Plates Dropping Core Temperatures to Below 0°C.[11]

Prices for liquid cooling systems can easily surpass $200, though newer systems can be bought for under $100.

A fan still must be attached to the radiator to help cool it, but it doesn’t have to spin as quickly as it would if it were attached to a heat sink. As a result, most liquid-cooled systems emit no more than 30 decibels.

Conclusion

Overclocking can be considered a subset of modding. This is a casual expression for modifying hardware, software or anything else to get a device to perform beyond its original intention. If you own an unlocked CPU you can get significant added performance, for free, by overclocking the processor. When modifying processor speeds, i.e. increasing them, high temperatures will occur. Higher performance cooling solutions are needed.

Fig. 7. YouTube Video of Overclocked CPU Melting Solder Before It Stops Working at 234°C.[12]

To serve the world of overclockers, a steady stream of air and liquid cooling systems are being developed. Many of them are high precision, effective, stylish and surprisingly affordable. Often they share the same technology as mass market quantity, lower performing cooling systems (basic heat sinks, heat pipes, for example), but provide much higher cooling capabilities for ever-increasing processor speeds.

References
1. Gamecrate.com, https://www.gamecrate.com/basics-overclocking/10239
2. Techreport.com, http://techreport.com/review/27543/cooler-master-hyper-d92-cpu-cooler-reviewed/3
3. Legitreviews.com, http://www.legitreviews.com/intel-devils-canyon-coming-this-month-intel-core-i7-4790k-core-i5-4690k_143234
4. Digitaltrends.com, http://www.digitaltrends.com/computing/should-you-overclock-your-pcs-processor/
5. Techradar.com, http://www.techradar.com/how-to/computing/how-to-overclock-your-cpu-1306573
6. Alcpu.com, http://www.alcpu.com/CoreTemp/
7. Coolermaster.com, http://www.coolermaster.com/cooling/cpu-air-cooler/hyper-212-evo/
8. Digitaltrends.com, http://www.digitaltrends.com/computing/heres-why-you-should-liquid-cool-your-cpu/
9. Coolermaster.com, http://www.coolermaster.com/cooling/cpu-liquid-cooler/nepton-280l/
10. Gizmodo.com, http://gizmodo.com/5696553/digital-storms-new-gaming-pcs-use-sub-zero-liquid-cooling-system-for-insane-overclocks
11. Digitalstorm.com, http://www.digitalstorm.com/cryo-tec.asp
12. Youtube.com, https://www.youtube.com/watch?v=9NEn9DHmjk0

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

Industry Developments: Cooling Electronics in Wind Turbines

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

(This article will be featured in an upcoming 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. To read the preceding post on Cooling Solar Power Inverters, click https://www.qats.com/cms/2016/11/21/industry-developments-cooling-solar-power-inverters.)

Wind power systems capture natural air currents and convert them, first to mechanical energy and then electricity. Windmills have long harnessed natural, renewable wind currents to grind grains and pump water. Now those windmills have evolved into highly engineered wind turbines, with very long, highly-engineered blades spinning on steel towers some that are tens of meters high.

There are some relatively small wind turbines that power individual houses or businesses. They can generate around 100 kW of power. But most of today’s wind turbine industry is for utility-scale power generation. These are large, tall wind turbines, in fields of dozens or hundreds, delivering high levels of electricity to power grid systems that reach thousands of end users. More than a quarter million of such turbines are in use around the world.

Cooling Electronics in Wind Turbines

Fig. 1. The Alta Wind Energy Center in California has more than 600 wind turbines and can produce more than 1.5 GW of power. [1]

Most utility-scale wind turbines are built on open, naturally windy land or off-shore. Each turbine can produce 1.0-1.5 MW, enough energy to power hundreds of homes. The United States has about 75 GW of installed wind power capacity. And, despite some local resistance, the U.S. has begun to join other countries with off-shore installations. China has by far the most installed wind power capacity at about 150 GW. Globally, the combined power capacity from wind turbines is forecast to nearly double between 2016 and 2020 to 792 GW. This would be enough to power 220 million average homes in the U.S. [2, 3]

Mechanics of Wind Turbines

When natural wind blows past a turbine, its blades capture the energy and rotate. This rotation spins a shaft inside the rotor. The shaft is connected to a gearbox that can increase the speed of rotation. The gearbox connects to a generator that produces electricity. Most wind turbines consist of a steel tubular tower. On top of this is a nacelle structure, housing the turbine’s shaft, gearbox, generator and controls.

On the wind-facing end of the nacelle is a hub to which the turbine blades are attached. Together, the blades and the hub are called the rotor. The diameter of the rotor determines how much energy a turbine can generate. The larger the rotor, the more kinetic energy is harnessed. Furthermore, a larger rotor requires a taller tower, which exposes the rotor to faster winds. [4]

A wind turbine is equipped with wind assessment equipment, including weather vanes. These send data to a computer to automatically rotate the turbines into the face of the wind and to a pitch system that can angle the blades to further optimize energy capture. [5]

Cooling Electronics in Wind Turbines

Fig. 2. The major components of a wind turbine. [6]

Turbines and Fire

Hundreds of wind turbines catch fire each year. The most common cause is lightning strikes, but overheated equipment can also be responsible. Highly flammable materials such as hydraulic lubrication oil and plastics are in close proximity to machinery and electrical wires inside the nacelle. A fire can ignite from faulty wiring or overheating. The results are catastrophic. The rush of oxygen from high winds can quickly expand a fire inside a nacelle. Once a fire starts, it is not likely to be deliberately extinguished. Water hoses can’t reach a nacelle’s height and wind turbines like these are typically set in remote locations, far from emergency aid. [7]

Cooling Electronics in Wind Turbines

Fig. 3. A wind turbine’s blazing nacelle and hub at a wind farm in Germany. Lubricating oil is often the fuel when these fires occur. [8]

Electronic Devices in the Nacelle – and Heat

Most wind turbines don’t catch fire, of course. Yet, despite all the surrounding wind, the electronics in their nacelles still need significant thermal management to function continuously. The most important electronics are the generator and power converting devices.

The generator is the heart of a wind turbine. It converts the rotational energy of the wind-spun rotor into electrical energy. It generates the electric power that the wind turbine system feeds into the grid.

Generating electricity always entails the loss of heat, causing the generator’s copper windings to get hot. Larger capacity generators are even further challenged. The thermal losses will increase with the generator in proportion to the cube of its linear dimensions, resulting in a serious decline in generator efficiency.[9]

Excess generator heat must be dissipated to maintain efficiency and avoid damage. On most wind turbines this is accomplished by enclosing the generator in a duct, using a large fan for air cooling. Some manufacturers provide water-cooled generators that can be used in wind turbines. The water-cooled models require a radiator in the nacelle to void the heat from the liquid cooling matrix.

Wind turbines may be designed with either synchronous or asynchronous generators, and with various forms of direct or indirect connection to the power grid. Direct grid connection means that the generator is connected to the (usually 3-phase) alternating current grid.

Wind turbines with indirect grid connections typically use power converters. These can be AC-AC converters (sometimes called AC/DC-AC converters). They change the AC to direct current (DC) with a rectifier and then back to usable AC using an inverter. In this process, the current passes through a series of Insulated Gate Bipolar Transistor switches (IGBTs). These convert direct current into alternating current to supply to the grid by generating an artificial sine wave. The more frequently the switch is turned on and off, the closer to a true sine wave the current flow becomes, and the more sine-like the flow, the purer the power. The resulting AC is matched to the frequency and phase of the grid. [10]

However, the faster these switches actuate, the more heat they develop and given a wind turbine’s variable inputs, IGBTs for this application need to cycle very frequently. This generates large amounts of heat that will dramatically decrease overall efficiency unless properly cooled. [11]

Cooling Electronics in Wind Turbines

Fig. 4. An active air cooling system inside a wind turbine nacelle features an air-to-air heat exchanger for managing heat in the generator (Vensys). [12]

Even with efficiency improvements, a wind turbine’s power generation systems and subsystems must manage ever increasing heat within its limited nacelle space. In addition, even if incurred power losses are as little as 3-5 percent, thermal management systems would have to dissipate 200-300 kW and more of heat.

Air cooling has been used effectively in small-scale wind turbines, but it is not practical for removing the heat produced in MW-scale units. Its thermal capacity is so low that it is difficult to blow enough air across a motor or through the converter to maintain reliable operating temperatures. That is why water cooling is used more often than air for larger wind turbines.

Cooling Electronics in Wind Turbines

Fig. 5. Electronics in a medium voltage (Up to 12 MW) wind turbine converter. Cooling is provided by a closed-loop unit with a mix of deionized water and glycol (ABB).[13]

However, water cooled systems are relatively large, and their thermal efficiency limitations force the size and weight of power generation sub-systems to essentially track their power throughput. Due to the thermal performance limitations of water, the power-generation equipment for a 10 MW wind turbine is nearly twice the size and weight of a 5 MW model. This is largely because water cooling cannot adequately remove additional heat loads without spreading them out.

One supplier of liquid cooling systems for wind turbine electronics is Parker Hannifin. Its Vaporizable Dielectric Fluid (VDF) system provides heat transfer capability significantly greater than that of water. The VDF system requires less fluid and lower pump rates. The same dissipation rates provided by a 6 liter/minute water flow can be achieved by 1 liter/minute VDF flow, thus allowing for a smaller system.

The hermetically sealed VDF assembly is designed to be leak proof, but if a leak occurs the non-conductive fluid will not damage electronic components. The cooling system’s efficiencies and lack of thermal stack-up provide an additional advantage in that the system maintains a fairly tight temperature range. The lack of thermal cycling removes a strain on the turbine’s electronics, which extends their useful life. [14]

Cooling Electronics in Wind Turbines

Figure 6. Dual-phase liquid cooling method for converters has a circulating refrigerant in a closed-loop. Vaporizing coolant removes heat from devices and re-condenses to liquid in a heat exchange (Parker). [15]

Conclusion

Heat issues in wind turbine electronics mainly concern the generator and the power conversion electronics. The heat load of the generator comes from copper wire resistance and from iron loss from the rotation of the core. Further heat loss is mechanical due to friction. These energy losses become heat energy that is distributed into the wind turbine nacelle.

The excess heat from the nacelle-based power conversion systems is mainly due to impedance from electronic components such as capacitors and thyristors. Higher temperatures will reduce the system’s life and increase failure rate. Thermal management methods such as liquid cooling can be effectively adapted for nacelle electronics. [10]

References
1. https://en.wikipedia.org/wiki/Alta_Wind_Energy_Center
2. https://en.wikipedia.org/wiki/Wind_power_by_country
3. http://www.ozy.com/fast-forward/how-twinning-tech-will-power-our-future/71993
4. Layton, Julia, How Wind Power Works, HowStuffWorks.com.
5. http://www.awea.org/Resources/Content.aspx?ItemNumber=900&navItemNumber=587
6. https://www.linkedin.com/pulse/smart-grid-energy-harvesting-martin-ma-mba-med-gdm-scpm-pmp
7. http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_17-7-2014-8-56-10
8. https://www.youtube.com/watch?v=sYoQ6mS2gss
9. http://ele.aut.ac.ir/~wind/en/tour/wtrb/electric.htm
10. Jian, S., Xiaoqian, M., Shuying, C. and Huijing, G., Review of the Cooling Technology for High-power Wind Turbines, 5th Intl Conf on Advanced Design and Manufacturing Engineering, 2015.
11. http://www.windpowerengineering.com/design/mechanical/cooling-electronics-in-a-hot-nacelle/
12. http://www.vensys.de/energy-en/technologie/generatorkuehlung.php
13. https://library.e.abb.com/public/430f5f2493334e4ead2a56817512d78e/PCS6000%20Rev%20B_EN_lowres.pdf
14. http://www.windsystemsmag.com/article/detail/60/cool-system-hot-results
15. http://buyersguide.renewableenergyworld.com/parker-hannifin-renewable-energy-solutions/pressrelease/parker-to-launch-converter-cooling-systems-for-1mw-wind-turbines-at-husum-wind-energy-2012.html

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