| Passive enhancement technology is without external power in technology of enhancing heat transfer method, so it has got great promotion and application in the industry. Heat transfer tube fitted with twisted tape is one of the most effective methods of passive enhancement technology, which can effectively enhance heat transfer, and play a better online antiscaling and descaling effect due to the twisted tape’s rotating. The helically twisted tape in heat transfer tube, which is a composite structure made up of the tape’s twisted spin and spiral line. Our predecessors have studied the twisted tape with structure of tape’s twisted spin or spiral line, which indicates heat transfer tube fitted with those twisted tape can improve the effect of heat transfer enhancement. On this basis, taking water as flow medium, an analysis on fluid flow and heat transfer of the heat transfer tube fitted with helically twisted is performed by experiment and numerical simulation.The experimental results have shown that the friction resistance, rotational characteristics and heat transfer coefficient of heat transfer tubes have a marked improvement after fitted with helically twisted tape. In experimental conditions, the frictional resistance coefficient and the Nusselt number of the tube fitted with helically twisted tape are20.07%-265.74%and14.49%-33.04%greater than those of plain tube; the rotational characteristics of the helically twisted tape is significantly higher than that of the smooth twisted tape, and its rotational speed is1.08～11.64times greater than that of the smooth twisted tape; and analyzes the influence of the width, twist ratios, helical pitch ratios and other parameters on pressure drop, rotational speed, heat transfer coefficient and Nusselt number; correlational equations are established by analyzing the experimental data with Multiple Linear Regression Analysis. Finally, in the Reynolds number present range of this experimental study, the comprehensive performance evaluation of heat transfer factorφ=1.063～1.587was observed by comprehensively estimating and analysis, and it indicated that the heat transfer enhancement of helically twisted tape is good.Through the numerical simulation for flow field and heat transfer of the twisted tape tube, the pressure, velocity, heat transfer coefficient and the temperature distribution in tube were analyzed. The simulation results show that, the streamlines in heat transfer tube fitted with helically twisted tape partly similar to the streamlines’characteristics of the smooth twisted tape and the spiral blade in tube, the spiral fluid’s rotating flow has strengthened the radial mixing of fluid and the disturbing in boundary layer, and due to the three-dimensional spiral shape of the flowing fluid, the time of fluid flow in the tube is more long; the flow velocity near wall region in heat transfer tube increase greatly after fitted with helically twisted tape, at the same time simulation shows there are speed vortexs in tube region; simulation calculation of heat transfer coefficient shows that the heat transfer coefficient of heat transfer tube fitted with helically twisted tape is greater than that of tube fitted with smooth twisted tape, and much greater than that of plain tube, the heat transfer coefficient of the tube fitted with helically twisted tape is2.80%～19.65%greater than that of the tube fitted with same torsion smooth twisted tape,5.56%～23.19%greater than that of plain tube; numerical simulation analyzes the influencing law of the structural parameters on pressure drop, rotational speed, heat transfer coefficient are consistent with experimental analysis laws. |
PDF Full Text Request