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With increasing demands for energy efficiency and compact system solutions, the development of innovative heat exchangers is becoming increasingly important [1, 2]. So-called Triply Periodic Minimal Surfaces (TPMS) play a particular role – these are mathematically describable, periodic surfaces characterised by a particularly favourable surface-to-volume ratio [3, 4]. The gyroid minimal surface, developed in the 1970s by Alan Schoen at NASA and defined by the equation sin(x)cos(y)+sin(y)cos(z)+sin(z)cos(x)=0, is a minimal surface characterised by low flow resistance and high mechanical stability [5, 6, 7]. In a recent research project at Mittweida University of Applied Sciences, such a heat exchanger was successfully developed, numerically simulated, manufactured using micro-SLM and validated on a test bench [8].
Manufacture using micro-SLM: 100 µm wall thicknesses in 316L stainless steel
At the Laser Institute of Mittweida University of Applied Sciences (LHM), a micro-SLM technology has been developed that enables the production of ultra-fine TPMS structures from 316L stainless steel (Fig. 1) [8]. The heat exchanger presented here has a cell size of 2.51 mm and wall thicknesses of 100 µm. The main challenge lay in the precise control of localised layer overgrowth. A modular design with constant wall thicknesses made it possible to stabilise the coating whilst simultaneously maintaining mechanical robustness through reinforced housing areas. Thanks to its low surface roughness (<10 µm), the component is ideal for precise thermofluid-dynamic applications [9].
CFD simulation using the SST-k-ω model and adaptive meshing
A coupled CFD approach was selected for the evaluation of the heat exchanger. The simulation was carried out in Ansys Fluent using the SST-k-ω turbulence model [4]. Polyhedral meshes and adaptive wall-following meshing (Fig. 2, left) were employed. Boundary layer modelling was improved using a specially developed tool which determines the Wimshurst boundary layer growth rate based on the Newton-Raphson method [10]. The simulation showed very good agreement with the experimental results – the heat transfer coefficient reached values of up to 12 kW/(m²·K) for a gyroid cell size of 1 mm, which corresponds to an improvement of over 300 per cent compared with conventional plate heat exchangers [11, 8].
Bench-top validation: water as the working medium
The heat exchanger was tested under counter-current conditions on the institute’s own test bench (Fig. 3) to validate the simulation. The water used flowed through the TPMS component, with inlet and outlet temperatures recorded via Pt100 sensors and the flow rate precisely controlled. A differential pressure sensor recorded the pressure drop.
The measurement results (Fig. 4) confirmed the simulation results: a heat transfer coefficient of over 8 kW/(m²·K) (Fig. 4c) was achieved with a low pressure drop of 60 mbar. By comparison, industrial high-performance heat exchangers achieve heat transfer coefficients of 4 kW/(m²·K) [11]. Particularly impressive was the high pressure stability of the structures, up to 8 bar – with no leaks [8].
Outlook: Future cell sizes and industrial applications
Further studies have already examined smaller cell sizes of less than 1 mm, which enabled even higher heat transfer coefficients [8]. However, the altered flow and boundary layer conditions require further analysis. With the new expertise in additively manufactured gyroid heat exchangers, future applications could be realised in the aerospace industry, in power electronics and manufacturing technology, or in hydrogen technology.
About the person
Justus Reuter began studying Mechanical Engineering at Mittweida University of Applied Sciences in 2020 and is currently undertaking his PhD under the supervision of Prof. Dr.-Ing. Uwe Mahn, investigating the influence of inlet systems on flow behaviour and heat transfer in additively manufactured heat exchangers. His research focuses on flow simulation, component analysis (FEM) and toolmaking.
Bibliography
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- Heinrich, F., Reuter, J., Erler, M., & Streek, A. (2024). Design and fabrication of a TPMS-based micro heat exchanger via micro selective laser melting. Presentation given at the Jena Laser Conference, Jena. Retrieved 21 May 2025, from Start – 14th Jena Laser Conference
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