NASA vehicles using cryogenic propellants and systems need improved cryogenic storage and transfer, including insulation for cryogenic transfer/feed lines. Wrapped multi-layer insulation (WMLI) is an innovative, next-generation, high-performance multilayer insulation designed specifically for cryogenic plumbing systems. WMLI uses Quest Thermal Group’s Discrete Spacer Technology to precisely control layer spacing, layer density, and minimize system heat flux. A customized discrete spacer, the Triple Orthogonal Disk (TOD) spacer, was designed, micromolded, and tested, and provides significantly lower heat leak than current state-of-the-art MLI insulation.
WMLI provides a superior, robust insulation for cryogenic feed lines, with a measured performance of 2.2 W/m2, which is 12 times better than traditional spiral-wrapped MLI insulation (26.6 W/m2). WMLI as vacuum jacketed pipe (VJP) could provide excellent thermal performance with heat flux as low as 0.09 W/m, compared to industry-standard VJP with 0.31 W/m.
With Discrete Spacer Technology, multiple radiant barrier layers are separated by discrete spacers in lieu of traditional netting. This produces an insulation system with numerous benefits, including higher performance, precisely controlled layer spacing and layer density, very robust bonded structures, excellent repeatability, and predictability. The TOD spherical micromolded polymer spacer maintains layer separation while having a very low thermal conductivity, partly due to design that minimizes thermal contact area/length (A/L). Attachment methods of the spacer could be achieved by bonding, snapping, heat staking, laser or ultrasonic welding. The spacer could also be a flowable mixture of low thermally conductive materials that is applied and cured in place during fabrication — creating a poston-demand.
Spacers are located on a metalized film in a predefined manner to meet requirements. Spacers can be arranged in a square, rectangular, trapezoidal, or triangular array to meet wrapping or geometry requirements. For a given installation, the spacing between adjacent spacers is maximized to minimize conducted heat.
Another innovation concerned WMLI wrapping techniques, including clamshell, helical, and faceted panel techniques. WMLI layers are applied to piping systems in a layered fashion. Panels or strips are fabricated with spacers pre-attached. As the layers are applied, a predefined spacing is created between adjacent layers causing the outer diameter to change according to spacer height. A number of layers are applied to meet insulation performance or spatial constraint requirements. Layers are overlapped to prevent radiative losses through open gaps or holes.
Wrapping with a faceted panel is primarily used for complex components such as corners or flanges. Each panel is designed to enclose the feature with small amounts of overlap to close out gaps and holes. The flat panel is defined to allow wrapping of compound curvatures with minimal distortion. The panel geometry changes per layer due to the interlayer spacing and therefore each is unique. The spacer layout is defined to provide adequate layer support while minimizing conduction. The preferred installation method for straight pipe runs is wrapping in a clamshell fashion along a length of pipe.
Another unique innovation developed was a method of nesting or layering of rigid shell parts. The theory for the discrete spacer technology was applied to a series of nested polymer shells to handle more complicated geometry such as tees, corners, valves, or manifolds. A series of layering parts is fabricated using rapid prototyping methods that minimize interlayer contact, reducing A/L for the nested shells, and thereby reducing thermal conduction. The benefits of this innovation are the capability of handling complex features, and reduction in installation cost and complexity.