(227d) Continuous Wire 3D Printed Sorbent Structures

To maintain an earth-like atmosphere on the International Space Station (ISS) and other spacecrafts, several different systems generate oxygen and remove unwanted gases. Specifically, CO2 and water vapor removal is critical for air revitalization on the ISS. A combination of zeolite molecular sieves and silica is used to adsorb CO2, water, and other trace contaminants. These adsorbed contaminants are then expelled by heating the sorbent bed to effectively regenerate it for further use. These beds are currently fabricated of loose beads with cartridge heaters and conductive fins embedded for heating. While cartridge heaters are a proven technology, their use for heating a bed of discrete spherical beads leads to high thermal resistance, extended heat-up/desorption time, and local hotspots. Additionally, packing a bed with loose beads provides minimal opportunity for optimizing the bed for pressure drop, flow rate, and adsorption capacity.

In conjunction with NASA, Mainstream Engineering is developing a process of fabricating advanced sorbent beds with a 6-degree-of-freedom additive manufacturing (AM) process. We are developing highly-loaded zeolite 13X and silica gel-based pastes that closely mimic the adsorbent capacity of the legacy sorbent beads. Using our custom AM system, we are able to deposit these pastes into 2.5D and 3D layers that are optimized for pressure drop, breakthrough capacity, and overall sorbent bed size and weight. Additionally, we have developed a patent-pending continuous-wire embedding mechanism and process that allows us to embed thin (34-40 AWG), high-resistivity wires directly into the printed roads. This process eliminates the need for external heaters, as we can electrify the wires that are embedded directly into the sorbent structure; enabling highly uniform and SWaP-optimized heating of sorbent structures. In preliminary testing, we have demonstrated heating a printed zeolite 13X structure up to 200 °C in under 10 minutes driven exclusively by an embedded wire. We are currently developing a test stand for automated performance and accelerated life testing for characterizing these beds.