Tag Archives: thermal management

Industry Developments: Cooling Nuclear Power Plants

Posted on October 7, 2016 by | 1 comment

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]

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.

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://commons.wikimedia.org/wiki/File:The_pressurized_water_reactor_of_NS_Savannah.jpg
[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

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Posted in cooling, Industrial, Nuclear Power, thermal management

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Case Study: Thermal Management in Harvard Medical School Tissue Analysis Instrumentation

Posted on October 4, 2016 by | Leave a comment

Designers of today’s highly advanced medical diagnostic equipment must overcome many of the same thermal challenges common to telecommunications, industrial and information technology electronics.

In addition, medical diagnostic devices present unique design issues and boundary conditions that factor into thermal solutions. These include isothermal and cyclic temperature demands, precise test repeatability, and maintaining the patient’s safety and comfort.

These kinds of issues were presented by Harvard Medical School to the experts at Advanced Thermal Solutions, Inc. (ATS) when it needed a cooling solution for the diagnostic equipment it was relying on for the analysis and observation of human tissue samples in a controlled laboratory setting. This was the school’s Frozen Tissue Microarrayer System.

ATS engineers had to provide thermal solutions to meet a range of design goals:

• Provide long-term temperature control for tissue samples embedded in an optimum cutting temperature fluid.
• Create a cooling system to maintain tissue samples below -70°C for six hours.
• Ensure operator visibility of the samples.
• Eliminate humidity and frost within the system to prevent sample contamination.

ATS Cooling Solutions

ATS engineers developed highly effective thermal solutions to meet all the design requirements of the diagnostic equipment. A reservoir in the device holds the liquid cooling medium and tissue samples are loaded through an opening at the top. Through a duct, cool air is circulated over the top of the samples to maintain temperature and humidity requirements.

As seen in Fig. 1 (below), the diagnostic system consisted of:

• Frozen tissue coring machine (on the right in the photo)
• Tissue sample loading area at the top of the cooling system (seen on the left)
• Duct system (on both sides of system) to circulate cool air
• Ice/alcohol reservoir at the system’s bottom to contain the cooling medium

Harvard Case Study

Figure 1. Prototype system created by ATS engineers for Harvard Medical School laboratory. (Advanced Thermal Solutions, Inc.)

Conduction Cooling Design

In operation, tissue samples are loaded into removable aluminum cassettes that fit tightly into a metal receiver (top left, Figure 2). The receiver contacts the cassette on five sides which allows for cooling of the samples by conduction. The receiver is lowered into a reservoir containing a slurry of dry ice and ethyl alcohol. Here the receiver is maintained at a constant temperature until the dry ice evaporates. The reservoir is double-walled and insulated to extend the evaporation time of the dry ice.

The receiver also features integral fins that increase surface area for drawing heat downward from the base of the cassettes into the icy slurry (bottom left, Figure 2). These fins are based on the same ATS heat sink design principles used in the company’s high performance maxiFLOW™ heat sinks.

Using analytical modeling, ATS engineers determined that 10 fins were the optimal number for cooling the cassette receiver and its contents. CFD simulations also showed that the 10-fin concept resulted in an optimal design. The engineers validated their analytical and CFD results through empirical testing. It was determined that extending 10 fins into the slurry provided the cooling performance to maintain tissue sample temperatures below the -70°C threshold for 9.75 hours.

Further temperature testing using thermocouples showed only a 2.5°C difference between the coldest points at the bottom of the fins and the tissue samples in the cassette. This proved that the design overcame thermal conduction resistance and could effectively maintain the samples below their critical temperature.

Figure 2. Temperature testing with thermocouples demonstrated that the temperature difference between the bottom of the fins and the top of the cassette, through three intervening layers, was only 2.5°C. This proved that the thermal design was successful. (ATS)

Figure 2. Temperature testing with thermocouples demonstrated that the temperature difference between the bottom of the fins and the top of the cassette, through three intervening layers, was only 2.5°C. This proved that the thermal design was successful. (ATS)

Figure 3. Using a heat sink-specific thermal resistance network ATS determined that the optimal number of fins was 10. (ATS)

Figure 3. Using a heat sink-specific thermal resistance network ATS determined that the optimal number of fins was 10. (ATS)

Convection Cooling Design

The above conduction cooling design provided only part of the solution. There were additional needs to maintain the temperature at the top of the samples and to decrease the relative humidity of the cool air from the ambient air in the lab. ATS engineers designed a convection cooling system to fulfill these requirements.

A heat exchanger was installed with its fins in the dry ice/alcohol slurry and its other side extending into a duct to cool the air passing over it. This approach uses the same cooling medium for both convection and conduction to ensure there is no temperature differential throughout the sample and that the sample is as isothermal as possible.

Air is pushed by a counter-rotating fan through the duct and into the heat exchanger. The heat exchanger forms a thermal link between this air and the slurry mixture. The heat exchanger was designed with an optimum balance between its surface area and the resulting pressure drop to ensure the fan was operating with the most effectiveness.

Once the air passes the heat exchanger, it moves through the ducts and into a diffuser at the top of the system. The diffuser disperses the air over the sample creating a barrier between the tissue and the ambient environment of the lab so outside moisture and heat are not transferred in.

The ATS engineers tested this design using an array of thermocouples and ATS hotwire anemometer Candlestick Sensors connected to an ATS ATVS-2020, a temperature and air velocity scanner. They determined there was too much mixing between the air flowing over the samples and ambient air. The diffuser was redesigned with a new connection to the duct and an optimized outlet radius (see Figure 4).

In the ducts, a molecular sieve desiccant housed in a honeycomb structure was used to reduce the dew point of the air to -84.4°C, which was well below the -72°C air temperature in the duct.

Figure 4. Initial testing led to a redesign of the air diffuser to prevent ambient humidity from mixing with the air over the tissue samples. (ATS)

Figure 4. Initial testing led to a redesign of the air diffuser to prevent ambient humidity from mixing with the air over the tissue samples. (ATS)

Conclusions

ATS engineers performed a final series of tests of the Frozen Tissue Microarrayer System using Candlestick Sensors, thermocouples and the ATVS 2020 scanner. The tissue temperature stayed constant over the required six-hour period and well below the -70°C threshold. In fact, testing determined that the tissue temperature remained below the threshold for nearly eight hours before warming above a usable temperature (Figure 5). The multi-part cooling system was a success, meeting the original design objectives provided by Harvard Medical School.

Figure 5. Final testing showed that the ATS cooling design kept tissue temperature (shown in blue in the graph above) below the -70°C threshold for more than the required six hours. (ATS)

Figure 5. Final testing showed that the ATS cooling design kept tissue temperature (shown in blue in the graph above) below the -70°C threshold for more than the required six hours. (ATS)

The process of designing cooling solutions for the Frozen Tissue Microarrayer demonstrated that thermal design practices used throughout electronics cooling can be applied in the medical device industry. Fin efficiency, thermal resistance, and pressure drop calculations are standard regardless of the application. Thermal solutions should be considered early in the design process so they can be incorporated into the overall system as efficiently as possible.

The experts at ATS used traditional thermal calculations, CFD simulations, empirical testing, and its leading-edge heat sink technology to successfully design the thermal solution for this medical equipment application. The ATS design allowed Harvard Medical School to test tissue samples while meeting its strict requirements.

To learn more about the design, watch the video below:

Download a PDF of this case study at http://www.qats.com/cms/wp-content/uploads/Harvard-Medical-case-study.pdf.

Visit www.qats.com, call 781-769-2800 or email [email protected] to learn more about ATS and its Thermal Management Analysis and Design Services.

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Dr. Reza Azizian Giving Nanofluid Presentation for PSMA Webinar

Posted on September 22, 2016 by | 3 comments

Reza Azizian

Dr. Reza Azizian, a research scientist at ATS and an expert on nanofluids, will speak about nanofluid technology as part of a PSMA webinar on Thursday, Oct. 6. (Josh Perry/Advanced Thermal Solutions, Inc.)


On Thursday, Oct. 6, Dr. Reza Azizian, a research scientist at Advanced Thermal Solutions, Inc. (ATS), a leading-edge engineering and manufacturing company focused on the thermal management of electronics, and an expert on nanofluid technology, nano-engineered surfaces, fluid dynamics, heat transfer and two-phase flow, will present “Nanofluids for Electric Cooling” as part of a webinar sponsored by the Power Sources Manufacturers Association (PSMA).

Dr. Azizian will join a panel of experts to discuss the enhanced heat transfer properties of nanofluids and their potential for the thermal management of compact, liquid-cooled electronics. Dr. Azizian will present an overview of the current stage of nanofluids technology, state-of-the-art research into nanofluid thermos-physical properties, convective heat transfer, and boiling heat transfer.

Prior to the webinar, Dr. Azizian sat down with the Josh Perry, Marketing Communications Specialist at ATS, to speak about his career, his interest in nanofluids technology, and the upcoming webinar.

JP: Thank you for sitting down with us. We want to highlight the work that the engineers are doing here at ATS, so I appreciate you taking a few minutes out of your schedule for this Q&A. I saw on your bio that you got your doctorate in Australia, is that where you’re from?
RA: Thanks for having me! No, originally I am from Iran and I did my undergraduate there; then I moved to Turkey and did my Master’s in Turkey. After that I moved to Australia and I did my Ph.D. in Australia. And then I ended up in Boston and did my post-doc at MIT.

JP: How did you end up at MIT?
RA: There is a very famous professor at MIT who was working on heat transfer in nanofluids back then. I invited him to Australia. He came and visited our facility in Australia and gave a talk and then he became interested in my research. Then he invited me over and during my Ph.D. I came to MIT as a visiting student and I was here for a year and then I went back to finish my Ph.D. and came back as a post-doc.

JP: How did you end up joining the team at ATS?
RA: It was four years ago as a visiting student. I have a very good friend in Australia and I was always interested in high technology, heat transfer, electronic cooling, and then he sent me the link to the ATS website and said, ‘Hey Reza, while you’re in Boston, you might want to visit this company.’ I thought, wow this is cool. I went through the website to see what ATS does and saw some fascinating projects done by ATS. So, I emailed Dr. Kaveh Azar and he responded to one of my emails and then that’s how we got in touch and then I visited the ATS facility, and coincidentally when I went back to MIT and I was talking to my supervisor and I said, ‘Oh, I went and visited this company and they’re doing a great job.’ He said, ‘Oh, the name is very familiar.’ We realized that when he graduated, something like 16 years ago, he applied here for a job and got a job offer but he got a position at MIT so now he’s a professor there. I kept my contact with Kaveh and then I went back to Australia and finished my Ph.D. After I came back to the U.S. as a post-doc, I invited them to MIT to come and visit our laboratory. So, we stayed in touch.

That’s how I came to know ATS and I realized that they are doing a great job in electric cooling and I was always interested because in electronic cooling there is no limit basically. Electronic equipment is becoming smaller and smaller every day and the only limit is thermal, at least at the moment. The only barrier is thermal issue for the advancement of electronic cooling and that’s why basically all of the funding from the Department of Defense, NASA, etc., it’s all on cooling. Because again, at this stage with all of these nanotechnologies and manufacturing capabilities, they don’t have any barrier to make things smaller except thermal. It’s a very interesting area of research and, you know, when you’re at the university you do cutting-edge research, which is cool, but it’s always nicer to do the research and then build something and use your knowledge in a more applicable way.

JP: Many of the people who read this will probably know, but what are nanofluids?
RA: Nanofluid is the term that you use when you disperse metal or metal oxide nanoparticles, which with the dimensions of 109 m, which is like .000000001 meter…very tiny, and you disperse these in your base fluid, whatever it is – could be water, oil, anything – and because they are tiny they are going to stay dispersed and at the same time because they are metal or metal oxide their thermal conductivity is going to be much higher than your base fluid. In simple language, thermal conductivity means the ability of the material to transfer heat. So, for example, for water the thermal conductivity is .6 W/mK, but for copper it’s like 400 W/mK, so you can assume that by mixing these two, again because the particles are tiny you will still have your liquid, which can easily flow, but at the same time it has higher thermal conductivity compared to the base fluid that you have.

The nanofluid term comes into play because of the heat transfer limitations that you normally have. In very general terms, there are two ways that you can increase the rate of heat transfer. One of them is increasing the surface area and the other is to increase the flow rate. Increasing the surface area, you are normally limited by the space that you have, right, and also increasing the flow rate you should use a bigger pump for example, to have a higher flow rate, which these are all costly. The only option left is if you can play with your working fluid and see how you can improve that and one of the ways you can improve that is by dispersing these nanoparticles to increase the overall thermal conductivity of your working fluid.

JP: How did you get interested in nanofluids? How did that become the focus of your studies and work?
RA: I’ve been working on nanofluids for the past 10 years. I came to know nanofluids during my Master’s and it was for my final-year project. I was looking for something cool and, even back then, nanotechnology was everywhere and then I was looking for something in the area of nanotechnology and heat transfer. I remember, my supervisor didn’t know much and he was like, ‘If you’re going to do this then you’re going to be on your own. I can’t help you much.’ It was funny, I went to the Internet to look up nanofluids and the first thing that came up was the name of this professor at MIT that I was working with during my post-doc. Back then, I remember I was sitting in my office and his name came up and I was telling my office mate, ‘This guy is cool. I’m going to go and work with him one day.’ And he laughed at me like, ‘Oh from here you’re going to go and work with him at MIT? Such a dream.’ And I’m here now.

JP: Obviously there is quite a bit more known about them now, how much has the subject matter changed in the 10 years that you’ve been studying nanofluids?
RA: The good thing is that now there are companies that are actually making nanofluids with very good stability – the particles don’t settle, they stay stable for a long time – and they commercialized a couple of nanofluids that are available now. They even use them in car engines, in the radiators, to increase the rate of cooling. They use it for CPU cooling. Next month, I’m going to go to Europe, there’s an event for the European Union, and they’re trying to basically commercialize nanofluids by 2020. They’re trying to see what are the barriers. The field’s improved a lot. The whole term of nanofluid was invented in 1999, so it’s only 17-18 years. So, it’s a fairly new area of research and seeing this technology commercialized now…the progress was quite fast.

JP: What will you be talking about in the PSMA webinar taking place on Thursday, Oct. 6?
RA: I’m going to be talking about nanofluids in general. What are nanofluids, basically, and what are the applications of nanofluids, in particular, in electronic cooling and high-powered electronics, which is the interest to PSMA. Then I’m going to give a brief explanation about the thermo-physical properties of the nanofluids followed by how they behave under laminar and turbulent flow conditions or even boiling for immersed cooling of electronics. And then I will conclude my talk by [explaining] what is the state-of-the-art and what are the future directions we expect nanofluids are heading to.

JP: Why do you think this is an important topic? Why do you think nanofluids are important as we go forward in the world of electronics cooling?
RA: These tiny particles, you add them to your working fluid and you don’t add much to the pumping power that you’re going to use because they are tiny, but at the same time you see 15-20 percent enhancement (depending on the nanoparticles and working fluid combination) in the heat transfer coefficient without changing any hardware. So, it has a very good potential and, again, this is only for single-phase heat transfer. In the case of immerse cooling of high-powered electronics, which boiling is the main heat transfer mechanism, we were able to see 200-250 percent enhancement in the value of critical heat flux by just changing the working fluid to nanofluid. It’s a very convenient way of doing it.

JP: Do you see nanofluids as the future of the industry? Do you see this is where electronics cooling is heading?
RA: I have to highlight that there are still problems with using nanofluids. This is why there is still research going on in this area. Stability is a big issue. You can use definitely some form of surfactant, which is a polymer that covers these particles’ surfaces and that keeps them dispersed. But in general if you don’t have that these particles, because they are tiny, they are under constant Brownian motion and when they become close to each other they stick to each other and then they agglomerate and they settle. So, there are still some issues that different research groups are trying to address but definitely it’s an area that I think is very useful for electronic cooling.

JP: Is research still going on here at ATS? Are you still really involved in the research and trying to find more applications for it?
RA: Yeah, yeah…we are always trying to push more towards using nanofluids. And hopefully we’ll see more in the future.

If you are interested in the PSMA webinar on Oct. 6, contact [email protected] no later than Oct. 4. For more information about Advanced Thermal Solutions, Inc., its thermal management products, testing equipment, and consulting services, visit www.qats.com.

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Posted in Consulting, Engineering, heat transfer, Liquid Cooling, Nano-technology

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What Cost Reduction Strategies Make New Product Introductions Faster?

Posted on September 19, 2016 by | 2 comments

Getting to markets faster and in the most cost-effective way is the primary goal of today’s product development process. Choosing a thermal design engineering partner that understands that goal makes a company’s product realization process simpler and faster. There are number of strategies a company’s project engineers can use to save time and money in the design of an electronics cooling solution. Two of the most efficient methods are Virtual Engineering Demos (VED) and Thermal Load Boards (TLB).

VEDs make it possible for project engineers to remotely see an instrument, how it operates, ask questions about how it works, and, if the project is included in the demo, get data in real time about a design. In this method, a live demo is setup at a thermal design engineering partner’s laboratory. Whether the project is a PCB, a system, or another product type, it can be included in the VED and be run through the lab set-up.

Greg Wong

ATS engineer Greg Wong gives a live, online demonstration from the ATS research lab to a potential customer. (John O’Day/Advanced Thermal Solutions, Inc.)

Candlestick Sensor

ATS engineer Greg Wong sets up to demonstrate the ATVS-2020, Candlestick Sensors and StageVIEW Data Acquisition Software (DAQ) for measuring and analyzing temperature for an electronics board in this VED. (Advanced Thermal Solutions, Inc.)

VED in Lab

Equipment setup and live camera feeds are all part of a VED setup. (Advanced Thermal Solutions, Inc.)

As the project is analyzed, data is shown on the engineering partner’s computer screen, which is in turn broadcast in real time to the project engineers via a live video feed. The video feed simultaneously shows the demo and the software’s operation, while allowing bi-directional conversation between the engineering partner and the project engineers in one or more locations.

stageVIEW_software

Screenshot showing data being recorded in stageVIEW. This information is available to the remote team. (Advanced Thermal Solutions, Inc.)

The advantages of this strategy to project engineers are:

• Quick evaluation of a design to determine if there is a need for new equipment in a project.
• No lag time in talking with a thermal design engineering partner about how to approach the thermal measurement of project
• Reducing the need to travel to a thermal design engineering partner’s lab.
• Faster response on lab testing, shortening the design cycle.

A Thermal Load Board (TLB) is another strategy for reducing the cost of a design, while getting a product to market faster. TLBs are created by a thermal engineering partner using a simple one- or two- layer non-populated PCB, heat sinks, thermally equivalent mock semiconductors and other mock components created with a 3-D printer.

TLB 3-D printing

Using these components a populated board is created that allows the testing of the heat sinks chosen for the project work and measurement of the airflow over the components and through the board. (Advanced Thermal Solutions, Inc.)

The thermal engineering partner is effectively creating a mock version of the functional board. The design of the TLB is based on the size and placement of the semiconductors and other components on the actual board, which is provided by the project engineers, and provides a cheaper and quicker means of producing a prototype for testing. The data from that testing will in turn expedite the design process and time to market.

This can be a very cost-effective method for doing heat sink characterization for the following reasons:

• It reduces electronic system development cost.
o A system developer can focus on thermal issues very quickly instead of waiting for an expensive prototype to come out of the factory.
o Rather than using a potentially expensive project, testing on prototypes can determine design flaws without requiring a significant
cost.
o Because prototypes are less expensive, each iteration of a design can quickly go through an initial series of tests.
• It reduces time to market.
o Valuable resources can be applied to engineering the best solution because a load board can generally be created in 1-2 weeks and at a
fraction of the cost of a full PCB.
• It allows a physical testing very early in the design.
o Many times components on a PCB will obstruct air flow, requiring either costly design changes during NPI (new product introduction) or
requiring engineers to over-design a board and the thermal management solution, putting the product outside its cost objective.

After a thermal load board is created, the board is ready to be used:

Completed Load Board

A completed load board ready for testing. (Advanced Thermal Solutions, Inc.)

The heaters on the board can be powered up to dissipate the same level of power as the semiconductors they are meant to represent. Heat sinks can then be applied based on initial analysis done via integral modeling, mathematical modeling or through CFD (computational fluid dynamics). To test just air flow, heat sinks can even be created by 3-D printing.

Once populated with heat sinks, the board can be tested in a wind tunnel to see if the air flow will be sufficient. Wind tunnel testing methods include smoke flow visualization or water tunnel testing in order to examine air flow and ensure the most functional and cost-effective design is applied.

Getting to market faster and with the best possible design is very important in today’s product development process. Working with a thermal engineering partner, such as Advanced Thermal Solutions, Inc. (ATS), that offers Virtual Engineering Demos (VED) and Thermal Load Boards (TLB) will benefit a project’s bottom line and ensure a project’s successful completion. Project engineers will know that their design has proper thermal management early in the process, meaning that they will not have to over-design the project, which will save time and money in the long run.

Learn more about ATS and its capabilities as a thermal engineering partner for your next project by visiting www.qats.com or by calling 781-769-2800.

References:

Thermal Load Board Design Considerations


http://www.3dsystems.com/learning-center/case-studies/lowering-cost-and-reducing-production-time-projet-3d-printing-lets

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Posted in Consulting, PCB, Simulation, Thermal Design

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Electric Car Batteries Are Topic of Presentation by ATS CEO Dr. Kaveh Azar

Posted on September 7, 2016 by | 7 comments
Electric Car Batteries

ATS CEO Dr. Kaveh Azar will deliver a presentation on the thermal management of electric vehicle batteries on Thursday, Sept. 22. (Photo courtesy of Wikimedia Commons)

On Thursday, Sept. 22, Advanced Thermal Solutions, Inc. (ATS), a leading-edge engineering and manufacturing company focused on the thermal management of electronics, will host the New England Section of Society of Automotive Engineers International (SAE NE) for a tour of its Norwood campus and a presentation by ATS founder, President, and CEO Dr. Kaveh Azar.

Dr. Azar’s discussion is entitled, “Battery Thermal Management – The Gateway to the Successful Operation of Electric Vehicles.” He will review the role of temperature in the longevity and performance of nickel metal hydride (NiMH) and lithium-ion electric vehicle batteries; drawing analogies between battery temperature and the junction temperature of modern electronics. As Dr. Azar notes, “Both play an identical role in successful operation of their respective systems.”

There will be a discussion of the analytical methods and design criterion for predicting battery temperature and establishing safe temperature limits. Dr. Azar will present high-level possibilities for thermal management in the electric vehicle sphere as well as cooling options that are deployed for battery thermal management. Current cooling designs can be active or passive. There are forced air, liquid cooling, natural convection and conduction systems used by manufacturers.

Several thermal solutions that engineers have incorporated include increasing the thermal density of the battery, using phase-change material to store transient heat loads and graphite-impregnated paraffin waxes as gap fillers. It is also important for the designs to control temperature distribution across the battery to avoid degradation of cells.

Thermal management is crucial in the design of electric vehicle batteries because temperature has a direct correlation on battery life and performance. It will affect the battery’s ability to store and deliver a charge, weaken polymer- or fiber-based cell dividers, and could potentially lead to thermal runaway.

“The engineers who will design the next hybrid vehicle battery packs will need to be cognizant of the growing need for thermal management,” read a recent article on coolingZONE. “The increased need for thermal protection, due to safety considerations; the reduced thermal capacity, due to lesser mass; and the reduced workable volume are among the challenges to be faced. The hybrid vehicle we may soon drive must have reliable and intelligent cooling systems to cool down their high-density battery packs.”

Why is this topic of particular relevance now?

Electric vehicle sales worldwide have jumped 57 percent from 2015 to 2016, according to data reported by Bloomberg New Energy Finance. The article referenced a Bloomberg report stating that electric vehicle sales could be as much as 47 percent of the automotive market by 2040 (dependent on factors such as oil prices). In the U.S., manufacturers have been urged by President Barack Obama’s EV Everywhere challenge to make electric cars as affordable and convenient as gas-powered vehicles by 2022.

Like cell phone technology in the past two decades, electric vehicles have the potential for widespread usage and to wide-ranging effects inside and outside of the automotive industry. The “digitization of the transport system” will effect, among others, oil companies, car dealerships, maintenance services, and utility suppliers.

“If it is hard to predict when phase change in complex systems begins, it is even harder to predict where it ends,” said Michael Leibreich and Angus McCrone, the authors of the Bloomberg article. “No list of potential impacts of the ‘Transformation of Transportation’ can be complete. However, one thing is for sure: if our predictions for the uptake of electric vehicles are anything like correct, there is no part of the global economy which will not, in some way, be affected.”

Currently, electric vehicles cost an average of $30,000 and travel 100 miles or less on a single charge. Tesla (Model 3) and Chevrolet (Bolt EV) have both promised electric vehicles that will travel 200 miles on a charge within the year. Other car makers, such as Volkswagen and BMW, have announced plans to turn a large portion of their production to electric vehicles in the next few years as well.

While the changes in infrastructure and the length of time that most car owners keep a vehicle (11 years on average) have limited electric vehicle sales to this point, according to Christopher Mims of the Wall Street Journal, the next vehicle that most consumers purchase is likely to be electric.

Mims explained, “It is the nature of disruptive technological shifts that it seems like nothing is changing—until it seems as if everything is changing at once. Electric vehicles have been a long time coming, but they now represent such a clear and present threat to the gasoline engine that Mr. Fox, of the service-station association, now recommends that members signing long-term contracts for fuel include an option to renegotiate if more than 10 percent of a state’s fleet goes electric.”

Electric vehicles offer a smooth drive with better acceleration, less moving parts requiring less maintenance, better air quality, and a better platform for autonomous driving, said Bloomberg. Electric vehicles are the future and that means designing better, longer-lasting, higher-performing batteries will be the future as well.

Cooling those batteries will be critical. As Dr. Azar will explain, without proper thermal management the electric vehicle battery will be inefficient and unable to provide the performance that consumers demand.

The Sept. 22 event is free for SAE NE members and $5 for non-members. It runs from 6-9:15 p.m. with tours of the ATS campus from 7-8:00 p.m. and Dr. Azar’s presentation at 8:00. Register online at http://www.sae.org/servlets/sectionEvent?PAGE=getSectionEvents&OBJECT_TYPE=SectionEventAdmin&HEIR_CODE=MS045#249128&saetkn=w1aFMMls8Y or contact SAE member Jeff Mobed at [email protected] or 508-367-6565.

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Posted in Analysis, Automotive, Manufacturing, Massachusetts Tech, Thermal Design

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