Twisted-tape-induced swirl flow heat transfer and pressure drop in a short circular tube under velocities controlled

Abstract

The twisted-tape-induced swirl flow heat transfer due to exponentially increasing heat inputs with various exponential periods ( Q = Q 0 exp( t/ τ), τ = 7, 14 and 23 s) and the twisted-tape-induced pressure drop were systematically measured with mass velocities, G, ranging from 4022 to 15,140 kg/m 2 s by an experimental water loop flow. Measurements were made on a 59.2 mm effective length which was spot-welded two potential taps on the outer surface of a 6 mm inner diameter, a 69.6 mm heated length and a 0.4 mm thickness of platinum circular test tube. The twisted tapes with twist ratios, y [= H/ d = (pitch of 180° rotation)/ d], of 2.39, 3.39 and 4.45 were used in this work. The relation between the swirl velocity and the pump input frequency and that between the fanning friction factor and Reynolds number ( Re d = 2.04 × 10 4 to 9.96 × 10 4) were clarified. The twisted-tape-induced swirl flow heat transfers with y = 2.39, 3.39 and 4.45 were compared with the values calculated by our correlation of the turbulent heat transfer for the empty tube and other worker's one for the circular tube with the twisted-tape insert. The influence of y and Reynolds numbers based on swirl velocity, Re sw , on the twisted-tape-induced swirl flow heat transfer was investigated into details and the widely and precisely predictable correlation of the twisted-tape-induced swirl flow heat transfer was derived based on the experimental data. The correlation can describe for the twisted-tape-induced swirl flow heat transfer for the wide ranges of twist ratios ( y = 2.39–4.45), mass velocities ( G = 4022–15140 kg/m 2 s) and Reynolds numbers based on swirl velocity ( Re sw = 2.88 × 10 4 to 1.22 × 10 5) within −10 to +30% difference.