Heat-transfer dependence of pipe surface materials in cryogenic double pipes

Abstract

Since the heat leak through the cryogenic vacuum chamber is a critical issue for superconducting devices, especially those with a large surface-to-volume ratio, such as a long cable, we measured the heat leak of the cryogenic co-axial double pipes for the superconducting cable in the past 20 years. We also estimate the heat leak using the radiative heat transfer equation for the cryogenic pipe. We can fix the surface area of the pipes from the design, but we have assumed the emissivity value of those surfaces. Therefore, we used the Fourier transform infrared spectroscopy (FTIR) and the optical integrating sphere to measure the reflectivity of various metal surfaces in the infrared wavelength range and estimate the effective emissivity using the Plank equation for the weighted average of the emissivity, a function of the wavelength. Finally, we estimate the heat leak utilizing the heat transfer equation and compare the experimental data. Since these two heat leaks are consistent, the optical measurement can potentially evaluate the surface performance of the cryogenic pipes. We also discuss the error of the optical measurements.