Fused filament fabrication (FFF, often called FDM) is widely used in polymer additive manufacturing; however, it suffers from mechanical anisotropy and weak bonding in the Z direction. This work examines how the infill pattern influences the tensile response of PLA parts at fixed printing conditions. Dog-bone specimens (PLA, four patterns: grid, honeycomb, rectilinear, adaptive cubic) were printed and tested in tension (n = 3 per pattern). Grid yielded the highest ultimate tensile strength, whereas honeycomb produced the largest Young’s modulus; rectilinear was intermediate and adaptive cubic was trailed in both metrics. X-ray diffraction of printed PLA showed a broad halo at 16–20° (2θ) with weak α-form reflections, consistent with largely amorphous microstructure after FFF. Together, the results indicate that, at constant material and nominal infill, pattern selection alone can shift the strength–stiffness balance, with grid favoring strength and honeycomb favoring stiffness.

For evaluating the heat transfer performance in a jet impingement cooling system featuring W-shaped rib turbulators, an experimental investigation was completed. Six different configurations, including three W-rib pitches ([ ], 9, and 6) and two jet-to-target surface spacings ([ ] and 6), were considered to completely assess their influence on the heat transfer, pressure loss, and crossflow of a relatively long impingement channel with an in-line array of [ ] impinging jets. Moreover, the regionally averaged heat transfer coefficients were evaluated based on two different reference temperatures: jet inlet temperature and local bulk temperature. Each configuration was experimentally tested at four Reynolds numbers, based on the jet diameter ([ ]), using the copper plate experimental method. The results show that the heat transfer enhancement can reach up to 25% in the narrow channel with the [ ] configuration. Also, the crossflow can deteriorate or enhance the local heat transfer along the channel. The discharge coefficients showed minimal variations, and the pressure loss increased in the W-rib channels is between 1.3 and 2.5 times the smooth channel pressure loss. Finally, a design correlation was developed for the area-averaged Nusselt number estimation in W-rib roughened impingement channels.