Prototype of a Semiflexible multi-layer Insulated Enclosure for Cryogenic Power Cables and Pipelines

Abstract

A 21 m long prototype of a semiflexible multi-layer insulated cryogenic envelope was built and tested to prove the suitability and economy of such a thermal insulation system for superconducting power transmission cables and liquid gas pipelines. The enclosure consists basically of an outer rigid tube at ambient temperature, a corrugated inner tube containing the cryogenic fluid, and superinsulation within the evacuated annulus. The flexible inner pipe is pulled into loosely connected rigid “spacer tubes” which are held coaxially to the outer tube by synthetic ropes. These spacer tubes serve also as winding cores for the insulation.

For the prototype which includes two 30°-bends, the cheapest possible insulation and structure materials were employed and the simple assembly procedures put to test. The inner cold cryogen duct and outer tube diameters are 100 and 273 mm respectively. Tests with liquid nitrogen and liquid helium as cryogens yielded satisfactorily low thermal losses of ≤0.6 W/m.