Experimental assessment of the parasitic thermal load on cryogenic envelope for superconductive cables

In the context of the hydrogen economy, transporting liquid hydrogen (LH2), instead of the gaseous one, is considered appealing due to the maximization of the energy density. The liquefaction of hydrogen is, however, an expensive process as it requires cryogenic conditions, typically in the range 20 K - 30 K, depending on operating pressure. To maximize the economic revenue from the transfer of LH2, the combination with other technologies requiring cryogenic operation can be considered, such as the power transfer through superconductors. Accurately quantifying the parasitic thermal load affecting the cable typically housed in a cryogenic envelope, is critically important. The Envelope is typically made of coaxial corrugated tubes to ensure flexibility and resilience against thermal contraction, facilitating connections between terminals and joints positioned at specific intervals. This study assesses the parasitic load through the envelope through boil-off measurements, relying on the correlation between the parasitic heating and vapor generation rate from liquid cryogen. Liquid nitrogen is selected as the cryogen, for the sake of availability, safety and cost. A lumped model is used to describe the behaviour of the system. It turned out that the parasitic load is ~2.1 𝑊 𝑚 at LN2 temperature. An extrapolation with the temperature range relevant for the LH2 operation results in +30% of the measured heat. These values match with the actual state of the art.