Explosive boiling of liquid nitrogen in a long thin tube and its application to the detection of a local temperature rise

To promote the commercial use of high-temperature superconducting devices, the ability to detect temperature anomalies easily and reliably and thereby protect the devices is important. In particular, a sudden local temperature increase due to a superconducting-to-normal transition can damage a device. In the present study, we propose a method to detect explosive boiling of superheated liquid nitrogen sealed in a long thin tube using a pressure gauge connected to the end of the tube. Experiments using a stainless-steel tube with an inner diameter of 1 mm and a maximum length of 50 m under various conditions showed that the local temperature rise caused explosive boiling at a temperature slightly below the superheat limit of 110 K for liquid nitrogen; the results also showed that the rapid pressure increase was transmitted to the end of the tube at approximately the speed of sound (similar to 830 m/s). The proposed method of placing a thin tube along high-temperature superconducting conductors or cryogenic structures can be used to easily detect a local temperature rise.