Investigation of the three-dimensional structure, pressure drop, and heat transfer characteristics of the thermohydraulic flow in a circular pipe with different twisted-tape geometrical configurations

摘要

The effect of inserting twisted tapes with various configurations and parameters inside a circular pipe on the flow field is studied. The pressure drop and turbulent heat transfer are investigated using the computational fluid dynamics (CFD) technique. Ten cases of heat exchanger pipes are considered numerically. The 3D Navier-Stokes, continuity, momentum, and energy equations are solved using Fluent software. To study the impact of the turbulent flow on the heat transfer performance, a scheme with the semi-implicit method for pressure-linked equations (SIMPLE) algorithm is adopted. Water is applied as the working liquid, with constant heat flux boundary conditions. The results show that insertion of a twisted tape has a strong effect on all the flow properties inside the pipe, such as the pressure, velocity, vorticity, and temperature. Moreover, the turning induced by the twisted tape can provide more effective mixing of the fluid and enhance the turbulent intensity, leading to a thermal boundary layer. It is reported that the maximum dynamic pressure occurs midway between the surface of the twisted tape and the pipe outlet. Such use of a twisted tape could lead to a greater pressure drop and make the flow in the pipe more unstable, due to influences of the stronger swirling flow and vortex flow as well as the effect of the increased turbulent intensity. The resulting strong swirling flow leads to an improvement in the heat transfer performance. The numerical results reveal that the introduction of a twisted tape efficiently increases the pressure drop and heat transfer, as well as improving the heat transfer performance by about 46.0%. Furthermore, the results indicate that insertion of a twisted tape can improve the thermal performance of the system.