Additive Manufacturing of a High Temperature, Ni-Based Superalloy Compact Heat Exchanger: A Study on the Role of Select Key Printing Parameters

Abstract

Compared to state-of-the-art heat exchangers, manifold-microchannel heat exchangers (MMHX) have shown superior heat removal density at moderate pressure drops. However, MMHX made of Ni-based superalloys or other tough-to-machine materials can be a challenge to fabricate using conventional fabrication methods, because of the inherently complex manifold microchannel geometry, as well as the required small feature sizes. In this study, a direct metal laser sintering (DMLS) additive manufacturing (AM) technique was used to fabricate the compact high-temperature MMHX reported here. The AM MMHX was fabricated as a single object, which significantly simplifies the fabrication process. In this work, three different AM machines were used to study the effect of laser power, powder size, and layer thickness on the fin and channel sizes of the fabricated MMHX. To evaluate the minimum wall thickness able to hold the design pressures, pressure containment tests were performed. As a result, a wall thickness of 0.3 mm was shown to withstand 340 kPa and be leakage-free. A detailed analysis of different printing orientations and their effect on the MMHX's design was also performed. Lastly, a 76×76×76 mm3 MMHX was successfully fabricated with fin thickness of 0.13 mm out of maraging steel. A second unit with dimensions of 94×87.6×94.4 mm3 was successfully fabricated with fin thickness of 0.22 mm out of Inconel 718. Details of the fabrication process and key takeaway results are discussed.

Experimental Characterization of an Additively Manufactured Inconel 718 Heat Exchanger for High-Temperature Applications

“…These measurements confirmed the predicted size, further validating the success of the print (see Ref. [39] for more info). HX was also tested under 340 kPa of pressurized air, and air tightness was demonstrated.…”

“…For example, some leftover powder was observed to be blocking some of the microchannels, and a few damaged fins were detected in the CT scan images (see Ref. [39] for more details), as depicted in Figure 7, which are discussed next. A combination of these factors could explain the difference in the pressure drop results, as discussed in the next section.…”

“…mance, as reported in Ref. [39]. This was made possible by orienting the part with a 45degree inclination with respect to the build plate.…”

“…Zhang et al fabricated the M2HX with inclined fins, which reduced its performance, as reported in Ref. [39]. This was made possible by orienting the part with a 45-degree inclination with respect to the build plate.…”

“…A detailed description of the printing procedure can be found in Ref. [39]. Once the printing was completed, the part was removed from the base plate via an EDM wire-cut process, and excess non-sintered powder was removed using an ultrasonic cleaner with deionized water.…”