Researchers at the Grainger College of Engineering at the University of Illinois Urbana-Champaign have used 3D printing to create a heat exchanger with a new design that offers dramatically improved performance.
Billions of heat exchangers are currently in use around the world. These devices, whose purpose is to transfer heat between fluids, are ubiquitous across many commonplace applications: they appear in HVAC systems, refrigerators, cars, ships, aircraft, wastewater-treatment facilities, mobile phones, data centres and petroleum refining operations, among many other settings.
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‘The design of heat exchangers, the mechanical geometry configuration of heat exchangers, has not changed in decades,’ said Professor Bill King, the Ralph A Andersen endowed chair of mechanical science and engineering. ‘The heat exchangers that we have today look almost exactly like the heat exchangers that we had 30 years ago. And the reason that there’s been so little innovation in heat exchangers has been that they are fundamentally limited by the manufacturing process.’
Precise design of the 3D shapes within these devices can optimise trade-offs among three key factors: the rate of heat transfer, the amount of work that must be applied to achieve the transfer and the size of the heat exchanger. But traditional manufacturing methods have meant that many desirable shapes were unachievable in practice.
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‘If you could have any shape at all, it might not be the shapes represented by existing heat exchanger technologies,’ King said. With 3D printing, however, the sky is the limit.
‘We can make many, many shapes – almost an infinite number of shapes that are not possible with today’s manufacturing technologies,’ said King. ‘And so we can make shapes that allow for complicated 3D geometries. We can link large passages for fluid flow that promote easy fluid motion, with small passages that promote high heat transfer. So we can make things that have three-dimensional shapes that allow fluids to be mixed and routed in unconventional ways.’
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In a project with the US Navy, the team successfully designed, made and tested an additively manufactured two-phase heat exchanger, meaning that the refrigerant comes in as a vapour and then cools down and leaves as a liquid, transferring its heat to cooling water that also flows through the heat exchanger. The device has complicated 3D geometries that significantly improve the heat transfer – geometries that couldn’t have been created with conventional manufacturing. By one measure, their heat exchanger outperforms traditional designs by 30 per cent to 50 per cent for the same amount of power.
‘Making better two-phase heat exchangers is critical for future energy-efficient systems,’ said Nenad Miljkovic, a founder professor of mechanical science and engineering. ‘With additive manufacturing, we increase the volumetric and gravimetric power density of the heat exchanger, resulting in lower mass and higher compactness. This results in a higher level of performance, and also enables the integration of high-power devices in mobile applications such as cars, ships and aircraft, which classically could not be achieved with state-of-the-art heat exchanger technology.’
As part of the research, the team developed modelling and simulation tools that allowed them to virtually test tens of thousands of possible configurations with different sizes, shapes and ways that flows would move back and forth within the heat exchanger. Those tools allowed them to explore and optimise within the huge design space enabled by additive manufacturing.
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The team is now continuing its work in this area, building out modelling capabilities further so that they can explore even more designs.
The research has been published in the International Journal of Heat and Mass Transfer.
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