Thermal diffusion of heat pulse in subcooled liquid nitrogen

Abstract

Transient heat transfer caused by a heat pulse in subcooled liquid nitrogen is investigated experimentally. This study is part of our ongoing efforts to develop a stable cryogenic cooling system for superconducting fault current limiters (SFCL) in Korea. A thin heater attached by epoxy on one surface of a GFRP plate is immersed in a liquid-nitrogen bath at temperatures between 77 K and 65 K. A strong heat flux up to 150 W/cm(2) is generated for 100 ms, and the temperature of the heater surface is measured as a function of time. The behavior of bubbles on the heating surface can be indirectly explained by comparing the measured temperature history for vertical and two different horizontal (up and down) orientations. It is concluded that subcooling liquid nitrogen below 70 K is a very effective method to suppress bubbles and result in better thermal protection and faster recovery from a heat pulse.