Visualization investigation of the full-field temperature of the damaged YBCO CC after quenching in liquid nitrogen based on bubbles distribution

Abstract

YBa2Cu3O7−δ (YBCO) coated conductor (CC) has a high critical temperature, which can be directly applied in liquid nitrogen. If the YBCO CC is quenched in liquid nitrogen, its temperature will rise rapidly, causing the liquid nitrogen to boil. The existence of nitrogen bubbles inhibits the heat dissipation of the YBCO CC, posing a challenge to the stable operation of the equipment. However, it is difficult to know how to effectively obtain the full-field temperature of the YBCO CC when it is quenched. In this paper, a liquid nitrogen bubble observation system was established with an oblique angle of 60°, and its front view was obtained using the perspective transformation method. Subsequently, we obtained a YBCO CC with only the YBCO layer containing damage and employed the H-formulation to solve the current distribution of the YBCO CC. We also calculated the temperature rise and heat flux of the sample. It is evident that near the damaged area heated up first. Additionally, it is found that nitrogen bubbles in contact with both surfaces of YBCO inhibit heat transfer, while nitrogen bubbles in contact with a single surface can be considered to have no effect. Therefore, it is recommended to remove the nitrogen bubbles on at least one surface of the YBCO CC.