Theses

Heat exchangers are essential thermal management systems across many industries, from aerospace to high-power electronics. The ambition to decarbonise these industries requires efficient and economically-feasible heat exchanger solutions. Preliminary studies on medium-capacity fuel cell–powered passenger aircraft suggest that heat exchanger designs would require width and height in the order of 1 m (Kozulovic, 2020;Frey et al., 2025), and thus amount to a significant proportion of the aircraft’s frontal area. It is therefore essential, for this and other related industries, that the next generation of compact heat exchangers can deliver the required heat rejection rates —which will necessitate large, intricate heat exchange cores — without incurring unfeasible penalties on fluid pressure drop. This is particularly challenging for gas-to-liquid heat exchangers because the gas-side is not as effective at transferring heat, so large flow rates are often required, leading to significant frictional losses (Kays and London,1998).

Additive manufacturing consists of a range of technologies with great potential to deliver novel and high-performing solutions to problems in a range of engineering disciplines, from structural to biomechanical to thermal. Combined with novel periodic lattice structures derived from the fields of crystallography and topology, promising heat exchanger geometries have been proposed in the scientific literature. In the past decade, these geometries have become increasingly appealing for two key reasons. Firstly, these structures can be readily manipulated using implicit modelling design tools, for which academic and commercial solutions have become widely available. Secondly, their cellular nature makes them easy to manufacture and implement into geometrically-complex design spaces.

Despite the excitement, much remains to be learned regarding the suitability of these geometries for gas-to-liquid heat exchange applications, on which this research focuses. For instance, there is a large amount of lattices based on Triply Periodic Minimal Surfaces available, each with distinct thermal and frictional performance characteristics. The same is true for strut-based lattice geometries. Furthermore, each of these structures can be functionally-manipulated, altering their performance characteristics. As such, engineers and researchers in this field are currently seeking to identify which geometries, topological features and manufacturing methodologies can help deliver the required levels of performance.

The aim of this thesis was to investigate the potential of and provide aerothermal (thermal and frictional) performance for heat exchanger designs based on periodic lattices. The objectives to meet this aim were multifaceted. Firstly, a novel meshing algorithm for minimal surfaces is presented which enables conversion to the standard CAD software format (BRep) early in the design workflow, offering a more traditional approach to CAD — among other benefits — as compared to other available options. Secondly, novel experimental techniques for internal pressure and temperature measurements in lattice structures are described and demonstrated, providing new insight into the flow and heat transfer mechanics within these lattices. Thirdly, experimental data are presented for a range of samples, including different lattice types (Gyroid and Diamond and strut-based lattices), different geometric properties (porosity and hydraulic diameter), different surface roughnesses, and different materials. The results, provided in dimensionless form, add to the limited data available in the literature, especially for this flow regime. Furthermore, recommendations for expediting experimental and simulation-based campaigns are made based on the findings. Much of this research was enabled by an experimental facility designed and commissioned as a part of this project.