Aluminum 3D Printed Radiator: How CELLSIUS Re-engineered Heat Exchangers with Additive Manufacturing
CELLSIUS, in collaboration with a student team from ETH Zurich, has rethought the heat exchanger structure for small hydrogen-powered aircraft through metal 3D printing, flow optimization, and monolithic design, achieving a better balance between cooling efficiency, weight, and drag.
A Radiator on an Aircraft is More Than Just a Cooling Component
This uniquely shaped radiator comes from CELLSIUS and an ETH Zurich student team currently designing a powertrain for their self-modified hydrogen-powered light aircraft.
For aerospace applications, a radiator is not merely an accessory; it is a critical component that simultaneously affects weight, drag, range, and overall aerodynamic performance. Every extra gram can impact flight efficiency, prompting the team to re-examine structures often overlooked in traditional radiators.
Traditional Header Tanks May Leave Much of the Cooling Area Ineffective
In traditional heat exchangers, beyond fin density and channel size, the header tank design directly impacts actual cooling performance.
If flow volume is too high in channels near the inlet, while the distant channels receive insufficient fluid, a significant flow unevenness occurs. In this state, even if the radiator has a large number of fins, a portion of the heat exchange area cannot function effectively, yet it still adds to the overall weight.
Simultaneously, an uneven flow field may also introduce additional pressure drop, requiring the pump to consume more energy to circulate the coolant.
3D Printed Monolithic Design: Header Tanks and Heat Exchanger Body Directly Integrated
The overall size of this radiator is about the size of two palms, with the dense holes on the right representing the air-side channels.
It is evident from the part's surface that there are no traditional welding, bolting, or assembly marks between the header tank and the heat exchanger body; it was formed in one piece directly through metal 3D printing.
The advantage of monolithic design is not just in reducing the number of parts, but more importantly, it allows designers to optimize flow distribution, channels, housings, and cooling structures simultaneously, without being restricted by traditional manufacturing and assembly methods.
Integration of the header tank and heat exchanger body reduces the need for extra welding and joints.
Material is retained only where it is truly needed, cutting out non-functional structural weight.
Internal structures can be generated freely based on fluid requirements, free from traditional machining constraints.
Thermal dissipation, pressure drop, weight, and printability can all be considered simultaneously.
Not "Drawing Shapes," but Letting Algorithms Generate Flow Field Structures
CELLSIUS's design approach does not involve deciding on a fixed geometric shape and then making fine adjustments.
The team sets available space, inlet/outlet locations, flow rates, and design objectives as constraints, then uses design tools to evaluate both flow and heat exchange performance simultaneously, gradually generating the final geometry.
One of the reasons they chose ToffeeX is its ability to perform multiphysics design and optimization directly for heat exchange between two fluids.
Forcing Coolant to the Far End to Improve Flow Distribution
After entering through the top-left inlet, the coolant does not flow directly into the first few rows of channels nearest the inlet; instead, it is guided toward the bottom of the cavity, flows laterally along the base, and is then distributed from the bottom up to more than ten channels.
The branched structure, which looks like biological tentacles from the outside, is actually a solid filling structure extending into the header tank.
These geometric features compress the proximal space, pushing fluid toward the distal areas that are otherwise harder to reach, while simultaneously occupying the areas within the traditional header tank where stagnant zones easily form.
More Uniform Flow, Lower Resistance, and Decreased Overall Weight
According to the team, the new design allows for more uniform internal flow velocity distribution in the radiator while reducing flow resistance and the required volume of coolant.
They cite research results indicating that if a traditional header tank is replaced with this type of optimized structure, the overall radiator weight can be reduced by approximately 20%.
The reason is not just that the header tank itself becomes lighter. When the flow field is more uniform, the same amount of cooling can be achieved with a shorter heat exchanger body; lower pressure drop can also further reduce the requirements for pumps, piping, and coolant.
Shortening the effective heat exchange structure through improved flow fields further reduces system weight.
Smoother fluid distribution lowers system resistance and pump load.
Lower coolant demand also saves weight, which is critical for aerospace applications.
Allows more heat exchange channels to participate in heat transfer rather than becoming dead weight.
Metal 3D Printing Must Also Consider Manufacturability
While this type of complex internal channel design is highly suitable for additive manufacturing, it does not mean that process constraints can be completely ignored.
When printing internal channels using metal powder bed fusion, it must be ensured that unmelted powder can be smoothly drained after printing, while minimizing the creation of unreachable internal supports.
Wall thickness of the housing must also be kept to a minimum without sacrificing forming stability or structural strength. Therefore, honeycomb reinforcement structures can use hexagonal stiffening meshes to provide support, allowing the outer shell to maintain a thin wall while withstanding internal pressure.
Why Choose AlSi10Mg Aluminum 3D Printing?
Looking at the header tank alone, its main task is just to guide and distribute fluid; it does not inherently require high thermal conductivity, so in theory, it could even be made of materials like nylon.
However, to truly leverage the advantages of metal 3D printing, the header tank and the heat exchanger body must be integrated directly into a single part, and the heat exchange region itself must possess excellent thermal conductivity.
Therefore, aluminum alloys suitable for metal additive manufacturing, such as AlSi10Mg, become a very logical material choice.
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