Design Complexity, Performance, and Cost Analysis in Additively Manufactured Manifold Microchannel Heat Exchangers

Abstract

The main objective of this dissertation is to investigate the tradeoffs among fabrication cost, design complexity, and thermal performance in additively manufactured metallic heat exchangers. Indeed, heat exchangers applications have become a favorite topic to investigate in diverse fields such as refrigeration, air conditioning, aerospace, and gas turbine engines. Specifically, high fabrication cost has emerged as the major drawback in the field of manifold microchannels heat exchangers (MMHXs). The potential for cost-effective fabrication has generated widespread interest in using additive manufacturing (AM) for manufacturing MMHXs. Moreover, superior capabilities of AM technologies can provide an opportunity for enhanced design of complex heat exchangers and superior thermal performance. In this dissertation, innovative MMHXs are designed and manufactured using powder bed fusion method. An experimental setup was developed to measure heat transfer and pressure drop for the additively manufactured MMHXs with various Reynolds numbers. A fabrication cost model was developed based on material cost for both inert gas and metal powder, machine cost, build time, and the volume of the part. The model was applied on EOS M280 and Renishaw machines which are the two most used powder bed fusion machines. The most important factor that can affect the cost, design complexity, and thermal performance of heat exchangers is the surface roughness. In this respect, a number of metallic flow channels with different shapes of cross sections were additively manufactured utilizing selective laser melting technology. Additionally, an experimental setup was designed to measure the pressure drop along the channel for various gas flow rates. The relationship between surface roughness along channels length and the pressure drop in the flow channels were investigated in order to predict the inner surface roughness by pressure drops. The results indicate that increasing design complexity in MMHXs does not necessarily improve the MMHX performance. However, adding more features or increasing design complexity increase fabrication cost in both EOS M280 and Renishaw AM400 machines. For surface roughness which is the significant factor influencing cost, design complexity, and thermal performance of heat exchangers, results show remarkable increase in the surface roughness for vertically manufactured channels along the build direction due to the combination of several factors.