Manufacturing the next generation of thermal management systems

Challenge

Creating an additively manufactured efficient solution for complex thermal management requirements.

Background

Emerging technologies in power electronics, aerospace propulsion and advanced heat exchangers demand thermal management systems that are not only efficient, but also compact and lightweight. Traditional manufacturing techniques often constrain the ability to produce the intricate, conformal geometries required for optimal thermal performance, leading to bulky, multi-component solutions.

Additive manufacturing (AM), or 3D printing as it is commonly referred to, presents a potentially useful approach to address some of these limitations, particularly through techniques like laser powder bed fusion (LPBF). Its layer-by-layer fabrication process allows for the creation of complex and novel designs that could otherwise be challenging to achieve through traditional means.

AM makes integrating multiple functionalities within a single component possible, potentially reducing weight and size, and allows for designs that are more tailored for effective heat dissipation. For this project, the aluminium alloy AlSi10Mg was selected due to its low density, good thermal conductivity and processability in LPBF systems.

Innovation

This project explored the application of AM in developing heat management structures with the potential for enhanced performance characteristics. AM's design freedoms were exploited and designs with intricate internal channels, fins and lattice structures were created, specifically using triply periodic minimal surfaces (TPMS) and gyroid patterns.

These architectures were chosen for their high surface-area-to-volume ratios, and their ability to induce beneficial turbulent flow regimes, enhancing heat transfer. They are geometries inherently unachievable with conventional manufacturing.

Designs were further refined using computational fluid dynamics (CFD) simulations to evaluate internal flow paths, ensuring both thermal performance and manufacturability. This involved taking into account factors like minimum printable wall thicknesses, overhang angles, and necessary support structures. Optimised, thin-walled structures were manufactured in AlSi10Mg material.

A significant challenge addressed was the removal of unmelted powder from complex internal geometries. A methodology was trialled involving optimising build orientation for gravitational powder flow and utilising advanced depowdering systems, with CT scans confirming the effectiveness of these cleaning strategies.

Result

Prototype heat exchanger designs were successfully fabricated in a cylindrical form factor (approximately 100 mm in height and 45 mm in diameter), demonstrating the viability of AM as a manufacturing method for complex heat exchanger designs using AlSi10Mg.

Flow testing of samples was conducted on a dedicated flow rig, with external heating applied to simulate real-world conditions. Relevant temperatures were measured using a combination of thermocouple and thermal camera apparatus.

Testing data for the AM-produced components showed varying levels of improvement in heat transfer characteristics, with heat transfer coefficients ranging from 100 to 450 watts per meter square per kelvin (W/m²·K), placing them within or above the performance envelope of conventionally manufactured aluminium heat exchangers.

Reynolds numbers -a dimensionless number that describes how turbulent a flow is - ranged from 3000 to 7000, indicative of transitional to fully turbulent flow regimes. Disruptive and turbulent flows can often benefit heat transfer rates, but these need to be balanced with their associated rise in pressure drop within the heat exchanger. Pressure drops varied from 30 Pascals (Pa) to 780 Pa depending on the internal geometry.

Overall, testing highlighted the need to balance thermal performance, pressure drop and manufacturability for all sample designs, as improvements in one area could be detrimental in others.

Impact

This project offered valuable insights and practical demonstrations of how AM might contribute to the design and production of heat management solutions.

By illustrating the possibility of creating compact, lightweight and performance-oriented structures with integrated functionality, such as gyroid lattices and conformal cooling channels, the project could contribute to improved energy usage through more efficient systems and enhanced performance via tailored thermal management.

This project highlighted the need to consider both thermal performance and manufacturability in the design process, demonstrating the trade-offs involved. It underscored the role of refined AM processing parameters and effective post-processing techniques in realising the full capabilities of AM for advanced thermal management applications.