Experimental study on fast quenching of cryogenic LN2 flow through interior micro-fin tube

Abstract

Future cryogenic vehicle requires a fast propellant fueling as well as a rapid pipeline quenching operation. In the present study, a novel interior micro-fin tube concept, with a series of cyclic fins arranged along the flow direction and has the size of 1 mm in both of fin height and fin width, is proposed to reach the purpose of cryogenic quenching acceleration. A cryogenic quenching test platform is established to evaluate the micro-fin effect. A straight tube and three micro-fin tubes, with fin intervals of 50, 100, and 200 mm, are fabricated and tested under different inlet Reynolds numbers (Re) conditions. The tube quenching cases covering inlet flow rate range of Re = 5000–45,000 are performed, and the results on temperature decrease, heat flux, and pressure drop are analyzed and compared. The test results demonstrate that the proposed micro-fin tube significantly reduces time cost in quenching process, and about 33–62% of time savings are reached for different Re conditions. The mechanism of micro-fin tube in facilitating quenching progress is that a radial velocity component within the annular vapor film could be induced by the micro-fin structure. This radial velocity acts on the liquid-vapor interface directly, which motivates interface fluctuation or tears the interface, and finally brings about an earlier liquid-wall contact at higher wall temperature. Moreover, it shows high heat flux appears immediately at the beginning of the quenching operation, and an approximately linear temperature decrease is experienced throughout the entire process. In addition, changing fin interval could affect the quenching rate under low Re conditions, but the fin interval influence decreases with the increase of Re. The test results show that the fin interval has slight influence on time cost when Re = 30,000. For a high-Re quenching event, a micro-fin tube with large fin interval could be suggested in the view of balancing consideration on heat transfer enhancement and flow resistance reduction. Compared to the surface treatment approaches, the proposed micro-fin structure tube provides a competitive approach in accelerating the quenching progress, and more work should be performed to optimize the micro-fin structure and the fin arrangement.