Investigation of the emittance properties of multilayer insulation used in cryogenic applications

Abstract Multilayer insulation (MLI) is one of the critical materials that is used to control radiative heat transfer in cryogenic systems. MLI consists of alternate layers of reflective aluminized mylar, separated by low thermal conductivity spacers. The thermal emissivity of the MLI layer plays a critical role in minimizing the radiative heat transfer through its layers. The native oxide formation is inevitable in any aluminized coating. This native oxide layer can affect the emittance of the reflective layer. This work aims to structurally and functionally characterize the reflective surface of MLI. Grazing incidence x-ray diffraction analysis indicates the presence of polyethylene terephthalate, and aluminum. Scanning electron microscopy analysis shows that the surface is uniform, and confirms the presence of C, O, and Al. Atomic force microscopy indicates a surface roughness of ∼4.7 nm. The total hemispherical emissivity is found to be 0.03 ± 0.01 and is compared with the estimated value from measuring the sheet resistivity using the Hagen-Rubens relation. While native oxide formation is inevitable, the measured results show that the reflective layer of MLI maintains its low emissivity due to the minimal thickness of alumina.