Performance Characterization of an Additively Manufactured Titanium (Ti64) Heat Exchanger for an Air-Water Cooling Application

Abstract

Over the last decade, rapid development of additive manufacturing techniques has allowed the fabrication of innovative designs which could not have been manufactured using conventional fabrication technologies. One field that can benefit from such technology is heat exchanger fabrication, as heat exchanger design has become more and more complex due to the demand for higher performance systems. One specific heat exchanger design that has shown significant performance enhancement potential over conventional designs and can greatly benefit from additive manufacturing technology is a manifold-microchannel heat exchanger. It is a design that combines careful fluid distribution through appropriate manifolds with an enhanced heat transfer surface design to achieve specific thermohydraulics performance expectations. Additive manufacturing allows fins as thin as 150 μm to be fabricated, which is an important enabler feature for the heat exchanger thermal performance. In addition, additive manufacturing allows the manifold and the microchannel sections to be fabricated as a single piece, which eliminates the need to fuse those sections together through a subsequent bonding process. As part of this work, we fabricated and experimentally tested a high-performance titanium alloy (Ti64) air-water heat exchanger that utilizes manifold-microchannel design. The heat exchanger was fabricated using direct metal laser sintering (DMLS) fabrication technique. The air-side implemented a manifold-microchannel design, while the water side used multiple rectangular channels in parallel. This was because the major thermal resistance occurs on the air side. The pressure drop and heat transfer performance of this heat exchanger were evaluated. The experimental results showed a noticeable performance reduction compared to the ones projected by numerical simulation due to an inaccuracy and low fidelity in printing of thin fin profile. However, despite this manufacturing inaccuracy, compared to a conventional wavy-fin surface, 15%–50% increase in heat transfer coefficient was possible for the same pressure drop value. Compared to a plain plate-fin surface, 95%–110% increase in heat transfer coefficient was possible for the same pressure drop value. The air-side heat transfer coefficient in the range of 100–450 W/m2K was achievable using manifold-microchannel technology for air-side pressure drop of 90–1800Pa. Since metal based additive manufacturing is still in the developmental stage, it is anticipated that with further refinement of the manufacturing process in future designs, the fabrication accuracy can be improved.