The use of additive manufacturing (AM) techniques allows for the construction of internal flow conduits whose cross-sectional geometries can vary from the traditional circular, square, or rectangular passages made using more traditional manufacturing processes. These internal channels have seen use in conformal cooling of molds and other fluid transport processes that take advantage of the ability to generate internal features previously unable to be fabricated. In the creation of these channels some AM processes also run into issue through the requirement of support structures that must then be removed in post processing. While many experimental studies have shown the feasibility of fabricating and using these channels, there has been less study into the fluid dynamics at play within the channels that are a function of the AM process parameters. The impact of layer thickness, build orientation, and even channel shape is of interest to the design of parts that take advantage of the new capabilities. By modifying the cross-sectional shape, the velocity gradients and thus frictional pressure losses will also be modified, in addition to affecting support structure requirements in fabrication. This creates an opportunity for interesting research relating to cross-sectional shapes that may reduce energy losses within a pipe system as compared to a circular cross section. In material extrusion AM, print parameters such as layer height and print orientation relative to flow orientation can also impact the wall friction. In this study a variety of material extrusion pipes were printed in order to experimentally study the effect of cross-sectional shape (circle, diamond, teardrop), print layer thickness and hydraulic diameter on the pressure drop through the pipe with horizontal full-developed turbulent flows. The hydraulic diameters studied for each shape are 3.5 mm and 5 mm while the print layer thickness of 0.127 mm and 0.33 mm were used. Reynolds numbers ranged from 9200–61,300 with a test fluid of water. The results demonstrate a significant effect of channel shape with the diamond and circle profiles resulting in the lowest and highest pressure drops respectively for a given flow rate. As the desired internal channel shapes are a function of ability to fabricate overhanging shapes with and without support material, these results provide valuable insight to designers who desire to both reduce internal pressure drops and fabricate parts with internal channels in AM. This is specifically valuable as most processes are able to fabricate a diamond shape without support structure necessary, eliminating the need for support removal steps.

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