Keeping it cool

Industrial cooling accounts for 7% of all electrical consumption in Western Europe and as the trend for faster, smaller, higher powered technology intensifies, the need for higher-performance, more energy efficient cooling systems will only increase

Although we may not always take notice, cooling plays a crucial role in maintaining the performance and reliability of a range of products – household and industrial – such as computers, car engines, x-rays and power stations. As these products continue to bear increasing heat loads due to additional power or a reduction in size, cooling has become one of the chief technical challenges facing high tech industry.

NanoHex (Nanofluid Heat Exchange) is an €8.3 million FP7 project, involving 12 leading organisations from Europe and Israel ranging from Universities to SME’s and major companies. NanoHex is the first step in overcoming the technological challenges faced in development and application of a reliable and safe nanofluid for more sophisticated, energy efficient, and environmentally friendly products and services. It aims to transform the future of heat management, combating heat build up in high tech industries with an innovative nanothermal fluid that has been shown to increase cooling efficiency by more than 40%.

Many industries currently employ heat transfer fluids such as water, glycol and oil,
but research has shown that the dispersal of particles smaller than 100nm (nanoparticles) into these fluids can significantly enhance their thermal capabilities.

Conventional cooling systems combat escalating heat loads by increasing the areas available for heat transfer or actively chilling coolants. But these methods are not cost effective and increase the size and complexity of the cooling equipment.

NanoHex will formulate a maximum performance commercial nanothermal fluid and develop operational nanofluid cooling systems for use by industries currently constrained by high heat loads and the rising cost of cooling. Data centres, electric vehicles and power generation are just three of the areas that NanoHex will explore, where the application of a nanothermal fluid has the potential to significantly improve energy efficiency, further advance technology and reduce costs.

“The concept of adding solid particles to a liquid in order to enhance its thermal conductivity is not new,” explains Mamoun Muhammed, Chair Professor at the Royal Institute of Technology Sweden and Scientific Director for NanoHex. Past attempts to incorporate millimetre or micrometre-sized particles into liquids have proved problematic, as particles settle and clog or erode the channels of the cooling system.

“What is new is that modern nanotechnology is now capable of producing nanoparticles smaller than 100nm, with some unique properties. Nanoparticles remain suspended in liquid longer and provide a much higher surface area, thus enhancing heat conduction far better than the fluid alone,” Muhammed added.

Size matters; materials at the nanoscale possess radically different physical properties as compared to bulk material. This means that altering their structure at this scale can change their behaviour. Even particles of the same size but a different shape can possess unique characteristics. By investigating a range of sizes, shapes, surfaces and compositions of nanoparticles, NanoHex can establish which nanofluid which will offer the highest heat transfer performance. 

Whilst nanopowders are already commercially available, there is currently no commercial source of nanothermal fluid anywhere in the world. NanoHex will work to establish nanofluids as a marketable product and manufacture them on an industrial scale. As with all new technologies, the adoption costs must be outweighed by the continued operating costs, the technological enhancement, and the financial return on investment.

“Persuading a company or client to change their current process and practice or adopt a new product is always difficult. Even if you can demonstrate a clear performance benefit, the adoption of any new technology always takes significantly longer than you anticipate,” explains Dr Andrew Round, commercialisation director for NanoHex.

“In an ideal world, our final nanothermal fluid could be directly incorporated into current liquid cooling systems, enabling companies to trial the fluid and see the benefits for themselves. But we also have to consider whether a redesign of the cooling system would further enhance the benefits,” he added.

The long term stability of the nanofluids presents further challenges that need to be met. Although initial studies have shown that nanoparticles remain dispersed for longer and cause less erosion than larger particles, the stability of nanothermal fluids over several years, as well as the overall wear and tear and long term performance of the system must be carefully considered. Furthermore, current research provides little data regarding the environmental health and safety of nanoparticles. NanoHex is conducting Environmental Life Cycle Assessments and Risk Assessments to ensure the production of a safe, stable, reliable nanothermal fluid.

Once complete however, a nanofluid’s ability to eliminate heat more efficiently than a regular coolant means less fluid would need to be used for the same cooling jobs. This opens doors for the design of smaller, lighter products and significantly reducing energy consumption, operating costs and carbon emissions.

Professor Yulong Ding, co-founder of NanoHex partner Dispersia comments: “If you want to increase heat transfer by a factor of two using current systems, you would need to increase the pumping power by a factor of about 12. If you have a better heat transfer fluid, which transfers heat quickly without much increase in pumping power, you would save a lot of energy.”

Nanofluid coolants will eventually be used to increase the efficiency, lower the weight and reduce the complexity of thermal management systems in existing and new production lines. They form an attractive option where there are tight limits on the size or weight of the cooling system, for example in computer servers and data centres, electric drives, transport and vehicles, and plant equipment and power generation.

Computer data centres account for 2% of global carbon emissions, a figure equal to that of air travel, with almost half of the energy consumed used in cooling. As thermal stress can directly impact computer performance, reducing throughput and reliability, most data centres rely upon the use of air conditioning or actively chill their thermal transfer fluids to keep their computer servers cool. However, as technology has advanced, microelectronics components have become smaller and more powerful, and now generate such large amounts of heat that cooling capacity is a major limitation to power density.

“One major area of concern is the growth in energy required to run data centres and communication rooms, which, on average, require 10-30 times more energy than standard office space,” comments Michael Cook, director of data centre company Usystems, “As we progress towards Web 2.0 and the high speed future of computing it is important not to be restricted by rising energy costs and tightening spatial constraints.”

A nanothermal fluid could be circulated through the data centre cabinets, directly to the most intense sources of heat, the processing chips. Removing more heat from the computer components with a more compact cooling system would allow the same processing power in fewer cabinets and increase the number of servers that could fit within each cabinet. The net result would be a significant reduction in capital expenditure on equipment and the amount of space needed to house it. 
The efficient removal of heat from computer servers, racks and cabinets using nanothermal fluid would also ease the demand for energy intensive air conditioning. This would result in lower energy costs and improvements to the environmental footprint of any facility.

Automotive companies are experiencing similar issues. Current power electronic components used in the electric drive applications of cars and trains suffer high temperature fluctuations as the power flowing through them is converted into heat. At present, in order to meet performance requirements, electric drive systems must incorporate large heat spreaders and, in extreme situations, resort to active refrigeration. An improved coolant would help to increase the power and efficiency of motors, whilst helping to reduce the costs.

It could also open the doors for new aerodynamic automotive designs that reduce emissions by lowering drag. An engine radiator more efficiently cooled by a nanofluid could be made smaller and placed elsewhere in the vehicle, allowing for the redesign of a far more aerodynamic chassis. Manufacturers of articulated trucks and lorries could benefit from these changes  because the shape of the front of their vehicles are currently constrained by the need for a large radiator at the point where air flows most freely into the vehicle’s structure. By reducing the size and changing the location of the radiator, a reduction in weight and wind resistance could enable greater fuel efficiency and subsequently lower exhaust emissions. Computer simulations from the US Department of Energy’s Office of Vehicle Technologies, showed that nanofluid coolants could reduce the size of truck radiators by 5%. This would result in a 2.5% fuel saving at highway speeds.

Enhanced cooling would also benefit the power electronics components of electric cars and trains. Specifically the insulated gate bipolar transistors (IGBT modules), that are used to drive the electrical engine and suffer the effects of high heat loads. The impact is a reduction in reliability and service lifetime. A nanothermal coolant that improves heat dissipation would allow these vehicles to carry a higher level of power, making the whole system far more efficient. It would also reduce wear and tear, and increase the shelf life of these power switches, extending the reliability of electric trains and cars, making them a more desirable product.

Wind Turbines and power stations are other industries that suffer high heat loads, which may benefit from a nanothermal fluid. All power generation produces waste heat as a result of the useful energy produced. Like electric cars and trains, both wind turbines and power stations incorporate the use of IGBT modules for the switching of power.
Placed together, power electronic IGBT modules form a converter that supplies a current with a variable frequency. Due to limited efficiency, these conversions produce large amounts of heat which can lead to thermo-mechanical fatigue.

“The same principles for cooling IGBT modules in electric cars and trains apply here,” explains Round, “The use of a nanothermal fluid coolant could help to improve the reliability of the equipment, reduce wear and tear, and increase the power electronics lifetime. The improvement in cooling would allow IGBT modules to carry a higher level of power. This enables engineers to develop reliable integrated cooling solutions that better meet the needs of their size, weight and shape to make the whole system far more efficient and cost effective.”

As energy prices rise, technology develops, and demand grows for higher performance products and processes, nanothermal fluids can offer a vital way to unlock the technological advances currently constrained by high heat loads and inefficient heat transfer.

"When we drafted the project we had only really considered rail and data centre applications, but we're seeing the same issues and application benefits across the board in industries that produce large amounts of redundant heat," concludes Round.