Thermosiphon Effect During Cooling Test of a 200 m DC HTS Cable Facility

Industrial application of HTS cables for power transmission is largely constrained by the imperfection of the cryogenic pumps that are expensive apparatuses providing additional heat load. Temperature and, consequently, density of the liquid cryogen change while it flows through the channel. If the cryogenic pipe route has enough elevation difference, this will lead to natural circulation. As a result, it may be not necessary to use pump, and the system cost and complexity will reduce significantly. The feasibility of the given approach was confirmed theoretically for various system configurations. Preliminary experiments were also carried out using 200-m dc HTS facility at Chubu University during the third and fourth cooling tests. Recently, during the sixth cooling test, the cryogenic pump was stopped intentionally. Meanwhile, the natural circulation of the liquid nitrogen was observed at flow rate of about 2 l/min, and the cable temperature remained low.