Natural Circulation Flow of Cryogenic Liquid for Superconducting Magnet Applications

An experiment to investigate the natural circulation of cryogenic liquid has been performed. The study is motivated mainly by our recent development of cryogenic cooling system for prototype superconducting cyclotron without any circulating pump. In the natural circulation loop system, a cooling channel is attached on the outer surface of the aluminum block and the liquid nitrogen passes through inside of the channel to cool the block indirectly. A cryocooler as a heat sink is located at the top to recondense cryogenic vapor coming from the aluminum block in which electrical heater is installed as a heat source. The main dimensions are determined using the relevant analysis, and the natural circulation loop is successfully fabricated. The temperature distributions in the loop are measured during initial cool-down process and in steady state, from which the modified Grashof numbers are calculated and compared with the existing correlation estimated with one-dimensional analysis for steady state flow.