Tag Archives: liquid cooling

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.

#JustChilling: ATS Recirculating and Immersion Chillers for Liquid Cooling Systems

ATS Chillers

Advanced Thermal Solutions, Inc. has a line of recirculating and immersion chillers for conditioning the coolant in liquid cooling systems. (Advanced Thermal Solutions, Inc.)


ATS offers a variety of chillers, including the CHILL V and CHILL iM series, for conditioning the coolant in liquid cooling systems. The ATS-CHILL V series, including the ATS-Chill150V, ATS-Chill300V, and ATS-Chill600V, are re-circulating, vapor compression chillers that offers precise coolant temperature control using a PID controller. The ATS-CHILL iM is an immersion chiller for precise control of the bath temperature by immersing the evaporator in a fluid bath.

Learn more about ATS recirculating and immersion chillers in this recent blog post or in the video below:

ATS Liquid Cooling Products

In addition to chillers, ATS has a complete product offering for Liquid Cooling Closed Loop Systems, including flow meters, leak detectors, heat exhangers, and cold plates. ATS can also design off-the-shelf or custom liquid cooling systems to meet the thermal needs of a project.

ATS 3-Core design approach identifies the type of cooling required at the analysis level and informs the client of its options, saving cost and time on design iteration and simulation verification. Once it is determined that liquid cooling is the option to pursue, the ATS design team identifies all the required components of the liquid loop, as well its packaging requirements and integration in the system.

ATS offers a complete array of off-the-shelf liquid loop components that can be readily deployed or custom-designed to meet the thermal requirements of the system. Subsequent integration of the liquid loop into the system provides the customer with a turn-key option for thermal management of their system.

Don’t get burned! Take advantage of ATS expertise in liquid and air cooling to ensure proper thermal management for your project.

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.

Cold Plates and Recirculating Chillers for Liquid Cooling Systems

Recirculating Chillers

ATS cold plates and recirculating chillers can be used in closed loop liquid cooling systems for high-powered electronics. (Advanced Thermal Solutions, Inc.)


The miniaturization of high-powered electronics and the requisite component density that entails have led engineers to explore new cooling methods of increasing complexity. As a result, there is a growing trend in thermal management of electronics to explore more liquid cooling systems and the reintroduction, and re-imagining, of cold plate technology, which has a long history that includes its use on the Apollo 11 space shuttle.i

Thermal management of high-powered electronics is a critical component of a design process. Ensuring the proper cooling of a device optimizes its performance and extends MTBF. In order for a system to work properly, engineers need to establish its thermal parameters from the system down to the junction temperature of the hottest devices. The use of cold plates in closed loop liquid cooling systems has become a common and successful means to insure those temperatures are managed.

Cold plate technology has come a long way since the 1960s. At their most basic level, they are metal blocks (generally aluminum or copper) that have inlets and outlets and internal tubing to allow liquid coolant to flow through. Cold plates are placed on top of a component that requires cooling, absorbing and dissipating the heat from the component to the liquid that is then cycled through the system.

In recent years, there have been many developments in cold plate technology, including the use of microchannels to lower thermal resistanceii or the inclusion of nanofluids in the liquid cooling loop to improve its heat transfer capabilities.iii

An article from the October 2007 issue of Qpedia Thermal eMagazine detailed the basic components of a closed loop liquid cooling system, including:

• A cold plate or liquid block to absorb and transfer the heat from the source
• A pump to circulate the fluid in the system
• A heat exchanger to transfer heat from the liquid to the air
• A radiator fan to remove the heat in then liquid-to-air heat exchanger

The article continued, “Because of the large surface involved, coldplate applications at the board level have been straight forward…Design efforts for external coldplates to be used at the component level have greatly exceeded those for PCB level coldplates.”

Exploring liquid cooling loops at the board or the component level, according to the author, requires an examination of the heat load and junction temperature requirements and ensuring that air cooling will not suffice to meet those thermal needs.iv

To read the full article on “Closed Loop Liquid Cooling for High-Powered Electronics,” click http://coolingzone.com/blog/wp-content/uploads/2017/01/Qpedia_Oct07_Closed_Loop_liquid_cooling_
for_high_power_electronics.pdf
.

Chillers provide additional support for liquid cooling loops

In order to increase the effectiveness of the cold plate and of the liquid cooling loop, recirculating chillers can be added to condition the coolant before it heads back into the cold plate. The standard refrigeration cycle of recirculating chillers is displayed below in Fig. 1.

Chiller,s Cold Plates

Fig. 1. The standard refrigeration cycle for recirculating chillers. (Adavanced Thermal Solutions, Inc.)

Several companies have introduced recirculating chillers to the market in recent years, including ThermoFisher, PolyScience, Laird, Lytron, and Advanced Thermal Solutions, Inc. (ATS). Each of the chiller lines has similarities but also unique features that fit different applications.

In order to select the right chiller, Process-Cooling.com warns that it is important to avoid “sticker shock” because of testing conditions that are ideal rather than based on real-world applications. The site suggests a safety factor of as much as 25 percent on temperature ranges to account for environmental losses and to ensure adequate cooling capacity.v

The site also noted the importance of speaking with manufacturers about the cooling capacity that is needed, the required temperature range, the heat load of the application, the length and size of the pipe/tubing, and any elevation changes.

“Look for a chiller with an internal pump-pressure adjustment,” the article stated. “This feature enables the operator to dial down the external supply pressure to a level that is acceptable for the application. Because the remaining flow diverts internally into the chiller bath tank, no damage will result to the chiller pump or the external application.”

When trying to decide on the right size chiller for your particular application, there are several formulas that can help make the process easier. Bob Casto of Cold Shot Chillers, writing for CoolingBestPractices.com, gave one calculation for industrial operations. First, determine the change in temperature (ΔT), then the BTU/hour (Gallons per hour X 8.33 X ΔT), then calculate the tons of cooling ([BTU/hr]/12,000), and finally oversize by 20 percent (Tons X 1.20).vi

Not every application will require industrial capacity, so for smaller, more portable chillers, Julabo.com had a secondary calculation for required capacity (Q).

Q=[(rV cp)material+(rV cp)bath fluid]ΔT/t

In the above equation, r equals density, V equals volume, cp equals constant-pressure specific heat, ΔT equals the change in temperature, and t equals time. “Typically, a safety factor of 20-30% extra cooling capacity is specified for the chilling system,” the article continued. “This extra cooling capacity should be calculated for the lowest temperature required in the process or application.”vii

Comparison of Industry Standard Recirculating Chillers

Recirculating Chillers

Applications for liquid cooling systems with chillers

Recirculating chillers offer liquid cooling loops precise temperature control and coupled with cold plates can dissipate a large amount of heat from a component or system. This makes chillers (and liquid cooling loops in general) useful to a wide range of applications, including applications with demanding requirements for temperature range, reliability, and consistency.

Chillers have been part of liquid cooling systems for high-powered lasers for a number of years to ensure proper output wavelength and optimal power.viiiix To ensure optimal performance, it is important to consider safety features, such as the automatic shut-off on the ATS-Chill 150V that protects against over-pressure and compressor overload. Other laser-related applications include but are not limited to Deep draw presses, EDM, Grinding, Induction heating and ovens, Metallurgy, Polishing, Spindles, Thermal spray, and Welding.x

Machine hydraulics cooling and semiconductors also benefit from the inclusion of chillers in liquid cooling loops. Applications include CVD/PVD, Etch/Ashing, Wet Etch, Implant, Inductively Coupled Plasma and Atomic Absorption Spectrometry (ICP/AA), Lithography, Mass Spectroscopy (MS), Crystal Growing, Cutting/Dicing, Die Packaging and Die Testing, and Polishing/Grinding.xi

One of the most prominent applications for liquid cooling, heat exchangers, cold plates, and chillers is in medical equipment. As outlined in an ATS case study,xii medical diagnostic and laboratory equipment requires cyclic temperature demands and precise repeatability, as well as providing comfort for patients. For Harvard Medical School, ATS engineers needed to design a system that could maintain a temperature of -70°C for more than six hours. Using a cold plate with a liquid cooling loop that included a heat exchanger, the engineers were able to successfully meet the system requirements.

Liquid cooling with chillers are also being used for medical imaging equipment and biotechnology testing in order to provide accurate results. ATS CEO and President Dr. Kaveh Azar will discuss the “Thermal Management of Medical Electronics” in a free webinar on Jan. 26 at 2 p.m. For more information or to register for the webinar, click https://www.qats.com/Training/Webinars.

Conclusion

Closed loop liquid cooling systems are not new but are gaining in popularity as heat dissipation demands continue to rise. Using cold plate technology with recirculating chillers, such as the ATS-Chill150V, ATS-Chill300V, and the ATS-Chill600V, to condition the coolant in the system can offer enhanced heat transfer capability.

Portable and easy to use, ATS vapor compression chillers are air-cooled to eliminate costly water-cooling circuits and feature a front LED display panel that allows users to keep track of pressure drop between inlet and outlet and the coolant level. They each use a PID controller.

Recirculating Chillers

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.

References
i http://history.nasa.gov/SP-287/ch1.htm
ii https://heatsinks.files.wordpress.com/2010/03/qpedia_0309_web.pdf#page=12
iii http://www.sciencedirect.com/science/article/pii/S0142727X99000673
iv https://www.qats.com/cpanel/UploadedPdf/Qpedia_Thermal_eMagazine_0610_V2_lorez1.pdf#page=16
v http://www.process-cooling.com/articles/87261-chillers-evaluation-and-analysis-keys-to-selecting-a-winning-chiller?v=preview
vi http://www.coolingbestpractices.com/industries/plastics-and-rubber/5-sizing-steps-chillers-plastic-process-cooling
vii http://www.julabo.com/us/blog/2016/sizing-a-cooling-system-control-temperature-process-heating-operations
viii http://www.laserfocusworld.com/articles/print/volume-37/issue-6/features/instruments-accessories/keeping-your-laser-cool0151selecting-a-chiller.html
ix https://www.electrooptics.com/feature/keeping-it-cool
x http://www.lytron.com/Industries/Laser-Cooling
xi http://www.lytron.com/Industries/Semiconductor-Cooling
xii https://www.qats.com/cms/2016/10/04/case-study-thermal-management-harvard-medical-school-tissue-analysis-instrumentation/

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.

Industry Developments: Cooling Nuclear Power Plants

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.)

Most man-made electricity in the U.S. is provided by thermoelectric power plants. In these large scale installations, water is boiled to steam to spin the plant’s turbines and to ultimately generate electricity. To provide the heat necessary to produce this steam, a power plant could burn coal, natural gas or oil. But, in fact, most plants don’t burn anything. Instead, they use a very hot, but carefully controlled core of nuclear material to provide the thermal energy for continuous steam.

Most large power plants use pressurized water reactors (PWRs) with nuclear fuel as their power source. There are different cooling requirements inside these plants and they are typically achieved with primary, secondary and tertiary thermal solutions. First, heat must be managed inside their reactor vessels where the radioactive material is housed. Then, in the steam generators, hot water from the reactor vessels is cooled by transferring its heat to a separated water source, converting it to steam. Lastly, after the steam moves past the turbines, it is condensed back to liquid water, which then returns to the steam generator. An illustration of a nuclear power plant with a pressurized water reactor is shown in Figure 1. [1]

Nuclear  Power Plant

Figure 1. Components of a Pressurized Water Reactor in a Nuclear Power Plant. [2]

Inside a PWR’s reactor core, the primary coolant, usually ordinary water, is heated by energy from atomic fission. Under high pressure to keep it from boiling, the heated water flows along a primary, closed-loop piping system into a steam generator. Here, the heat from the primary loop transfers into an isolated, lower-pressure secondary loop also containing water.

The water in the secondary loop enters the steam generator at a pressure and temperature slightly below that required to initiate boiling. Upon absorbing heat from the primary loop, it becomes saturated and slightly super-heated. The water changes phase to steam, which serves as the working fluid to push the turbine blades and generate electricity.

Finally, the steam is condensed back to water and re-enters the secondary loop. There are different ways to provide this tertiary level of cooling to cause this condensation. [3]

Fueling a Nuclear Reactor

A nuclear power plant’s reactor is most often fueled by U-235, a type of uranium that fissions easily. U-235 is a component of uranium hexafluoride fuel, which is made from mined or milled uranium oxide, called yellowcake. To make the uranium hexafluoride usable as a fuel, it is enriched to increase its U-235 content from 1 percent up to 3-5 percent. This is a low concentration and the enriched uranium is stable over a wide range of environmental conditions.

After the uranium hexafluoride is enriched, a fuel fabricator converts it into uranium dioxide powder and presses the powder into solid fuel pellets. The fabricator loads the ceramic pellets into long, pencil-thin rods made of a noncorrosive material, usually a zirconium alloy. These tubes, each about 4 meters long, are grouped by the hundreds into bundles that are called fuel assemblies. [4]

Figure 2. A Pressurized Water Reactor Includes Inlets and Outlets for Passing Water Coolant. [5]

Figure 2. A Pressurized Water Reactor Includes Inlets and Outlets for Passing Water Coolant. [5]

A single fuel rod assembly for a pressurized water reactor (PWR) is approximately 13 feet high and weighs about 1,450 pounds. [6]

Step 1. Cooling the Nuclear Core

During a nuclear fission chain reaction, fuel rods heat up to about 800°C. If they are left uncovered by water, they’ll reach temperatures well about 1,000°C and begin to oxidize. That oxidation will react with any water that remains in the vicinity, producing highly explosive hydrogen gas. So, fuel rods are kept submerged in demineralized water, which serves as the primary coolant. The water is kept in a pressurized containment vessel and reaches about 325°C. [7]

At the atomic level, continuous exothermic fission in the fuel rods releases heat into the water in the PWC’s reactor. Nuclear power plants manage this fission and its resulting heat with the use of control rods. The rate of fission can be controlled–even stopped–by inserting and removing the control rods in the reactor. The control rods are made with neutron-absorbing material such as cadmium, hafnium or boron. Their presence controls the rate of nuclear reaction by absorbing neutrons, which otherwise would contribute to the fission chain reaction.

Figure 3.  Control Rods Manage the Fission Rate Inside Nuclear Reactor Cores. [8]

Figure 3. Control Rods Manage the Fission Rate Inside Nuclear Reactor Cores. [8]

A single uranium fuel pellet the size of a fingertip contains as much energy as 17,000 cubic feet of natural gas or 1,780 pounds of coal. This relatively clean energy property, along with its vast half-life (700 million years), makes U-235 a viable alternative to burning fossil fuels to turn power plant turbines. [6]

Control Rod Drive Mechanisms (CRDMs) lower, raise, and keep in position assemblies of control rods inside a nuclear reactor. The rods absorb free neutrons, limiting the number available to cause fission of nuclear fuel. [8]

Step 2: Heat Transfer in Steam Generators

In a PWC-style nuclear power plant, the primary coolant, carrying heat from the reactor core, flows through a looped system into and out of a steam generator. Inside the generator it transfers its heat to an isolated, secondary coolant, water, converting it to steam. This steam travels in a secondary loop to the turbines. The transfer of heat from the primary loop to the secondary loop is accomplished without mixing the two fluids to prevent the secondary coolant from becoming radioactive.

Figure 4. Illustration of a Steam Generator. [9]

Figure 4. Illustration of a Steam Generator. [9]

There are multiple generators in a nuclear power plant. Each can measure up to 70 feet in height and weigh as much as 800 tons. A generator has more than 10,000 tubes, adding up to hundreds of miles in total length. A steam generator’s tubes are in a U-shape formation and each tube is about 19mm in diameter. Coolant from the reactor enters the generator’s inlet nozzle and circulates through the U-tubes.

The secondary coolant flows upward by natural convection through the bundle absorbing heat from the tubes of primary coolant. As heat is transferred through the tube walls, the secondary coolant, water, is turned into steam that flows from the top of the generator.

The materials that make up the steam generators and tubes are specially made and specifically designed to withstand heat, thermal expansion, high pressure, corrosion and radiation. The tubes are an important barrier between the radioactive and non-radioactive sides of the plant. For this reason, the integrity of the tubing is essential in minimizing the leakage of water between the two sides. [9]

Figure 5.  Steam Generator Tubes Transfer Heat from the Primary to the Secondary Loop. [8]

Figure 5. Steam Generator Tubes Transfer Heat from the Primary to the Secondary Loop. [8]

Step Three: Condensing the Steam

Once the steam has passed through a turbine, it must be cooled back into water by a third process and returned to the steam generator to be heated once.

Figure 6. Simple Illustration of Recirculation Scheme for Power Plant Steam. [10]

Figure 6. Simple Illustration of Recirculation Scheme for Power Plant Steam. [10]

There are three main methods of cooling a power plant’s steam and residual hot water:

Once-through systems take water from nearby sources (rivers, lakes, oceans), circulate it through condensers, and discharge the now warmer water to the local source. Once-through systems were initially popular because of their simplicity, low cost, and the abundant supplies of cooling water. But these systems can cause disruptions to local ecosystems, mainly from the large water withdrawals.

Wet recirculating systems reuse cooling water in a second cycle rather than immediately discharging it back to the original water source. Typically, wet recirculating systems use cooling towers to expose water to ambient air. Some water evaporates, but the rest is sent back to the condenser in the power plant. Because wet-recirculating systems only withdraw water to replace what’s lost through evaporation, these systems have much lower water withdrawals than once-through systems. Before being fed into the steam generator, the condensed steam (referred to as feed water) is sometimes preheated in order to minimize thermal shock.

More recently, plants have started using a third type of steam cooling system called dry cooling. Instead of using water to lower cooling water temperature, these systems use air passed over the cooling water by one or more large fans. Running those fans can require a significant amount of electricity, which makes this system less suited for large plants that require a lot of steam such as those powered by coal or nuclear energy. [11]

Three Integrated Cooling Systems

The illustration below is a simplified look at the main cooling loops in the Davis-Besse nuclear power station in Ohio. It features a pressurized water reactor in which uranium fuel is in long metal fuel rods (1) leading down to the reactor core (2). The reactor core is inside the reactor vessel (3) which is filled with purified water. Control rods (4) on top of the reactor start and stop the chain reaction that produces heat. When the rods are withdrawn, the nuclear chain reaction occurs, producing heat.

Figure 7. The Three Main Cooling Loops in a Nuclear Power Plant. [12]

Figure 7. The Three Main Cooling Loops in a Nuclear Power Plant. [12]

The water inside the Davis-Bessie PWR is under pressure so it won’t boil as its temperature rises by passing through the nuclear core. The water then travels along tubes through the steam generator (5) and back to the reactor. This constitutes the primary loop (green). After it has passed through the steam generator, the water has cooled down. The average temperature in this cycle is maintained at 582°F.

When the primary coolant water passes through the steam generator, its heat is transferred to the secondary loop (blue). Heat is transferred without the water in the primary loop and secondary loop ever coming in contact with each other. The water in the secondary loop boils to steam in the steam generator. This steam flows to the turbine generator (6). It is here that the steam’s energy is made into electricity.

When the steam leaves the turbine, it comes in contact with pipes carrying cooling water. As the steam cools, it changes back into water. The third loop (yellow) contains the water that is cooled by the large cooling tower (7). [12]

Among all of the power plants in the US, just over half reuse their cooling water. The rest are either dry systems or hybrid systems which can switch between dry and some sort of wet cooling depending on the temperature and availability of water.

References:
[1] Bright Hub Engineering, http://www.brighthubengineering.com/power-plants/2722-components-of-nuclear-power-plant-coolant/
[2, 3] http://www.world-nuclear.org/information-library/nuclear-fuel-cycle/nuclear-power-reactors/nuclear-power-reactors.aspx
[4] https://en.wikipedia.org/wiki/Nuclear_reactor_core
[5] https://www.britannica.com/technology/nuclear-reactor/Coolant-system
[6] Nuclear Energy Institute, http://www.nei.org/Knowledge-Center/Nuclear-Fuel-Processes
[7] http://energy.gov/sites/prod/files/2014/01/f7/csp_review_meeting_042313_martin.pdf
[8] Vallourec, http://www.vallourec.com/NUCLEARPOWER/EN/products/nuclear-island/Pages/crdm.aspx
[9] http://cdn.intechopen.com/pdfs-wm/14150.pdf
[10] Union of Concerned Scientists, http://www.ucsusa.org/clean_energy/our-energy-choices/energy-and-water-use/water-energy-electricity-cooling-power-plant.html#.V8i9Cs9ATct
[11] https://en.wikipedia.org/wiki/Pressurized_water_reactor
[12] http://www.co.ottawa.oh.us/ottawacoema/davisbesse.html