PERFORMANCE CHARACTERISTICS OF DEEP CORRUGATED TUBES WITH TWISTED-TAPE INSERTS

Recent investigation of the performance characteristics of some passive compound heat transfer enhancement techniques revealed that the combination of corrugated tubes with twisted-tape inserts seems to be a very attractive enhancement technique for single-phase turbulent flow. This holds in the range of height-to-diameter ratios e/D-i > 0.04 and small relative pitches of the twisted tape, H/D-i. This paper presents the latest results of an experimental investigation of the friction factors and heat transfer coefficients (inside with water as working fluid and outside with condensing steam) of eight single-start, spirally corrugated tubes with geometrical parameters: 0.053 < e/D-i <0.089 and ridge pitch-to-height ratio 6.8 < p/e < 11.0 combined with twisted tapes with H/D-i = 4.7, 5.7, and 7.6, in the range of Reynolds number, 3.5 x 10(3) < Re < 5.0 x 10(4). The increase of outside heat transfer coefficient E-0 is presented as a function of geometrical parameters of the depth of the corrugated tube through the Weber number, We, and the relative pitch of the twisted tape H/D-i. The effect of Reynolds number on E-0 is discussed.