关键词: 强化传热, 流动阻力, 扭曲管, 二次流

Abstract: In the literature survey on twisted tubes (TTs), it can be found that many documents believe that TTs are processed from round tubes based on the method of equal cross-sectional area, ignoring the fact that the cross-sectional perimeter of TTs is approximately constant during processing. In addition, the research on the cross-sectional shape on the heat transfer characteristics in the TT is relatively rare. Based on this, the heat transfer characteristics of the fluid in the TT with typical cross-sectional shape under low Reynolds number (Re) are analyzed by simulation on the basis of experimental validation. The results show the regularly spiral deformation of the TT induces periodic spiral flow of the fluid inside it, and the secondary flow is generated in the direction perpendicular to the mainstream, which reduces the synergy angle between temperature gradient and velocity and intensifies the convective heat transfer of the TT in contrast to that of round tube with equal cross-sectional circumference. When Re ranges from 650 to 1550, the TTs corresponding to the convective heat transfer coefficient from high to low are twisted triangle tube, twisted rectangular tube, twisted oval tube, twisted square tube and plain tube, respectively. The convective heat transfer coefficient and flow resistance of the twisted triangle tube increases 1.94~1.97 times and 2.96~3.06 times than plain tube, respectively. All the TTs outperform the plain tube in terms of comprehensive heat transfer performance and the comprehensive heat transfer performance evaluation factor of twisted triangle tube is the highest, with an average of about 1.86, and the rest are twisted rectangular tube, twisted oval tube and twisted square tube, which can be summarized that the twisted triangle tube performs the best convective heat transfer performance. Although the optimal tube shape is the twisted triangular tube, cold-rolling the cross-section into a triangular shape requires high toughness and is not easy to form. In practical applications, extruding the round tube into a rectangular or elliptical cross-section can be considered. The above research on the influence of cross-sectional shape on the heat transfer characteristics in TTs has practical significance for guiding the optimization design of novel TTs.

Key words: heat transfer enhancement, flow resistance, twisted tube, secondary flow