[3D Printing] Topology Optimization Case Study of an Aluminum Alloy 3D-Printed Radiator

Aircraft Radiators: More Than Just a Heat Dissipation Component

This uniquely shaped radiator was developed by CELLSIUS and a team of students from ETH Zurich. The team is designing the power system for a hydrogen-powered light aircraft they have modified themselves.

In aviation, a radiator is not merely an accessory; it is a critical component that impacts weight, aerodynamic drag, range, and overall aerodynamic performance. Since even an extra gram of weight can affect flight efficiency, the team began to re-examine structures that are often overlooked in conventional radiator design.

Conventional Distribution Manifolds May Fail to Utilize Full Dissipation Area

In conventional heat exchangers, it is not just fin density or channel dimensions that affect actual heat dissipation performance, but also the distribution manifold.

If flow is concentrated in channels near the inlet, preventing sufficient fluid from reaching distant channels, a significant imbalance occurs in the flow field. In this scenario, even with a high number of fins, part of the heat transfer surface remains ineffective, adding only to the total weight.

Furthermore, an uneven flow field can create excess pressure drop, requiring the pump to consume more energy to circulate the coolant.

Monolithic 3D Printing: Directly Integrating the Distribution Manifold and Heat Exchange Core

The radiator is approximately the size of two palms. The dense holes on the right represent the air-side flow channels.

Looking at the surface of the part, it is clear that the distribution manifold and the heat exchange core lack the typical traces of welding, bolting, or assembly, as they have been produced as a single piece via metal 3D printing.

The benefit of monolithic manufacturing goes beyond reducing the number of parts. More importantly, it allows for the simultaneous optimization of fluid distribution, flow paths, housing, and heat dissipation structures, free from the constraints of traditional processing and assembly methods.

Generating Structures via Algorithms to Control Flow, Rather Than Designing Shapes

CELLSIUS’s design methodology does not involve defining a fixed shape and then refining it.

The team first sets constraints such as available space, inlet/outlet locations, flow rate, and design targets. The design software then evaluates the flow field and heat exchange performance simultaneously, generating the final form incrementally.

One reason for choosing ToffeeX was its ability to perform multiphysics design and optimization directly for heat exchange between two fluids.

Guiding Coolant to Distant Areas to Improve Flow Distribution

After entering from the top-left inlet, the coolant is not directed straight into the channels nearest the inlet, but is instead guided to the bottom of the manifold. From there, it flows laterally along the bottom before being distributed into over a dozen channels from the bottom up.

The branching structures, which resemble biological tentacles, are actually solid filler structures extending into the interior of the distribution manifold.

These shapes narrow the space near the inlet, forcing fluid toward distant areas where it would be difficult to ensure flow otherwise. Simultaneously, they fill areas where fluid typically stagnates in conventional distribution manifolds.

Flow Uniformity and Reduced Resistance Lead to Overall Weight Reduction

According to the team, the new design results in a more uniform flow velocity distribution within the radiator, while simultaneously reducing flow resistance and the volume of coolant required.

Research cited by the team suggests that replacing a conventional distribution manifold with such an optimized structure can reduce the total weight of a radiator by approximately 20%.

The reason for this is not just the weight reduction of the manifold itself; a uniform flow field allows the same heat dissipation to be achieved with a shorter heat exchange core. The reduction in pressure drop also potentially decreases the scale of the pumps and piping required, further reducing the necessary coolant volume.

Manufacturability Must Also Be Considered in Metal 3D Printing

While such complex internal channel designs are suitable for additive manufacturing, the constraints of the manufacturing process cannot be completely ignored.

When printing internal channels using laser powder bed fusion, it is essential to ensure that unmelted powder can be reliably removed post-print. It is also critical to avoid internal supports that cannot be removed.

The wall thickness of the housing must also be kept as thin as possible without sacrificing printing stability or structural integrity. Therefore, a honeycomb-like reinforcement structure composed of hexagonal rib grids is used to maintain a thin outer shell while ensuring it can withstand internal pressure.

Why Choose 3D Printing with AlSi10Mg Aluminum Alloy?

The primary role of the distribution manifold alone is to guide and distribute fluid. Since it does not require high thermal conductivity, it could theoretically be manufactured from materials like nylon.

However, to fully capitalize on the advantages of metal 3D printing, the distribution manifold and heat exchange core must be integrated into a single component. Furthermore, excellent thermal conductivity is required in the area where heat exchange occurs.

For this reason, aluminum alloys suitable for metal additive manufacturing, such as AlSi10Mg, represent a rational material choice.