CHARACTERISTICS OF FALLING FILM FLOW ON SHELL SIDE OF TUBE-WOUND HEAT EXCHANGERS WITH ROUND AND FLAT TUBES

Abstract

Abstract: In order to investigate the characteristics of falling film flow on the shell side of a special-shaped tube-wound heat exchanger, a three-dimensional physical model of the tube-wound heat exchanger was established, the multi-phase flow model based on the volume of fluid (VOF) method was numerically simulated, and the characteristics of falling film flow outside the tube of circular tube and flat tube were compared and analyzed. The results showed that the axial distribution of the falling film flow outside of the round tube and the flat tube showed the shape of "trough-peak-trough", and the falling film flow velocity of the flat tube was obviously higher than that of the round tube. The thinnest part of the outer liquid film of the round tube was at 120° of the circumferential angle of the round tube, and the thinnest part of the outer liquid film of the flat tube was at 90°- 120°. With the increase of pipe spacing, the average liquid film thickness of the round tube and the flat tube showed a downward trend, and the circumferential average film thickness of the flat tube was 10%-29% thinner than that of the circumferential average film thickness of the equal circumference of the round tube. With the increase of the winding angle, the circumferential average film thickness of the flat tube was 4%-28% thinner than that of the circumferential average film thickness of the circumferential round tube. Therefore, it is recommended to use the flat tube instead of the round tube as the winding tube of the winding tube of the tubular heat exchanger.

Key words: spiral wounded heat exchanger, round tube, flat tube, liquid film thickness, numerical simulation, VOF model

References

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