DESIGN AND PERFORMANCE CHARACTERIZATION OF AN ADDITIVELY-MANUFACTURED HEAT EXCHANGER FOR HIGH TEMPERATURE APPLICATIONS

Abstract

In its early stages of development, additive manufacturing was used chiefly for prototyping, but over the last decade, its use has evolved to include mass production of certain products for numerous industries in general, and speciality industries such as biomedical and aerospace industries in particular. Additive manufacturing can be used to fabricate unconventional/complex designs that are difficult and time-consuming through conventional fabrication methods, but offer significant performance advantage over state of the art. One such example is high temperature heat exchangers with complex novel geometries that can help improve the heat transfer density and provide better flow distribution, resulting in more compact and efficient designs and thereby also reducing materials costs considering fabrication of these heat exchangers from the suitable super alloys with the conventional manufacturing techniques is very difficult and laborious. This dissertation presents the results of the first high-temperature gas-to-gas manifold-microchannel heat exchanger successfully fabricated using additive manufacturing. Although the application selected for this dissertation focuses on an aerospace pre-cooling heat exchanger application, the results of this study can still directly and indirectly benefit other industrial sectors as heat exchangers are key components of most power conversion systems. In this work, optimization and numerical modelling were performed to obtain the optimal design, which show 30% weight reduction compared to the design baseline. Thereafter, the heat exchanger was scaled down to 66 × 74 × 27 mm3 and fabricated as a single piece using direct metal laser sintering (DMLS). A minimum microchannel fin thickness of 165 μm was achieved. Next, the additively manufactured headers were welded to the heat exchanger core and the conventionally manufactured flanges. A high-temperature experimental loop was next built, and the additively manufactured heat exchanger was successfully tested at 600°C with ~ 450 kPa inlet pressure. A maximum heat duty of 2.78 kW and a heat transfer density close to 10 kW/kg were achieved with cold-side inlet temperature of 38°C during the experiments. A good agreement between the experimental and numerical results demonstrates the validity of the numerical models used for heat transfer and pressure drop predictions of the additively manufactured heat exchanger. Compared to conventional plate-fin heat exchangers, up to 25% improvement in heat transfer density was achieved. This work shows that additive manufacturing can be used to fabricate compact and lightweight high temperature heat exchangers, which benefit applications where space and weight are constrained.