Thermal and flow characteristics of a cylindrical superheated steam generator with helical fins

Abstract

Helical fins including the downward (−30°), flat (0°), and upward (15°, 30°, 45°) fins were applied to the inner wall of a high temperature steam generator (HTSG) in the same direction as superheated steam flowing in the HTSG, to improve heat transfer performance. The flow inside the HTSG and the temperature change were analyzed using numerical analysis. Without a fin, the numerical analysis results showed a difference of up to 11.6% for superheated steam and 5.1% for hot gas compared with the actual experimental temperature readings. When steam was introduced into the HTSG, a secondary vortex flow was generated around it, along with a descending swirl flow and the application of helical fins inhibited downward flow and increased the time that the steam received heat from the superheater. In addition, the upward type fin prevented the escape of the superheated steam from the upper surface of the fin better than the downward type fin, in which the curved surface of the fin faces downward of the HTSG. The secondary flow occurred between the HTSG wall and the fins, which contributed to the improved of heat transfer. The highest temperature of steam discharge was at an upward fin angle of 15°.