Numerical Study on Heat Transfer and Flow Characteristics for Laminar Flow in a Circular Tube with Swirl Generators

This study investigated the heat transfer and flow characteristics of one kind of swirl generator in a circular heat exchanger tube through a numerical simulation. The swirl flow induced by this type of swirl generator can obtain a high heat transfer rate with minimal pressure drop penalty. The simulations were carried out to understand the physical behavior of this kind of mesoscale heat enhancement component. By visualizing the heat transfer and flow characteristics, it is found that the swirl flow is induced by swirl generator in the circular tube couples with the impinging jet effect. After passing through the swirl generator, the local friction factor of liquid can quickly return to lower level more quickly, while the local Nusselt number maintains higher values for a distance; thus, the evaluation criterion of local performance is improved. Single-factor optimization is used for three geometric parameters, i.e., the angle of swirl generator (25º, 45º, and 60º), the length of swirl generator (0.005, 0.01, and 0.02 m), and the center rod radius (1, 2, and 3 mm). The optimum parameters of the swirl generator for laminar flow of air in a circular tube are obtained, which should be 60º, 0.005 m, and 3 mm, respectively.