Additive Manufacturing of Heat Exchangers: A Case Study on a Multi-Layered Ti-6Al-4V Oscillating Heat Pipe

Thompson, S.M., Aspin, Z. S., Shamsaei, N., Elwany, A., & Bian, L. (2015). Additive Manufacturing of Heat Exchangers: A Case Study on a Multi-Layered Ti-6Al-4V Oscillating Heat Pipe. Additive Manufacturing. Elsevier. 8, 163-174. DOI:10.1016/j.addma.2015.09.003.

Abstract

Additive manufacturing (AM) allows for layer-by-layer fabrication of complex metallic parts with features typically unobtainable via conventional manufacturing. For heat exchangers, such complex features are desirable for enhancing their heat transfer capability and conformability to specific applications. In this case study, Selective Laser Melting (SLM), a laser-based additive manufacturing process, was utilized to fabricate a compact (5.08 cm × 3.81 cm × 1.58 cm) flat-plate oscillating heat pipe (FP-OHP) with innovative design features, including a Ti–6Al–4V casing and a closed-loop, circular mini-channel (1.53 mm in diameter) consisting of four interconnected layers. Venting holes were integrated to intersect each layer to allow for a unique layer-by-layer, plug-and-pressurize de-powdering procedure. The device channel surface was inspected via Scanning Electron Microscopy (SEM) – and it was found that the channel wall consisted of partially un-melted particles, as well as amorphous melt regions; surface characteristics influential on surface/fluid capillarity and heat transfer. This study also highlights important design and manufacturing concerns encountered during SLM of channel-embedded parts, such as channel surface quality and de-powdering. The Ti–6Al–4V FP-OHP was found to operate successfully with an effective thermal conductivity of approximately 110 W/m K at a power input of 50 W; demonstrating a 400–500% increase relative to solid Ti–6Al–4V.