Numerical study on heat transfer in a tube with conical-mesh frustums inserted

Abstract

In this work, an innovative enhanced heat transfer tube (EHTT) is proposed, inserted with segmented conical-mesh frustums. The diameter of the bottom surface and the pitch between conical frustums were investigated while the diameter of the tube and apex angle are fixed at 20 mm and 60o, respectively. The ratio between the height of the frustum and that of the sliced part was set as a golden ratio (1.618), which is regarded as the optimal in nature. Numerical simulations were employed to study the performance of the enhanced heat transfer tube in the laminar flow region and the effects of the parameters on performance were compared. To save the workload and time of simulation, the equal equivalent diameter and total flow area criteria were adopted to simplify the 3-Dimensional mesh pores to 2-Dimensional mesh pores. Besides a multiscale grid system was built to link the micron scale of the mesh pores and macroscale of the tube and periodic boundary conditions were used. The results demonstrated that the flow and temperature fields were modeled effectively, with larger velocity and velocity gradient in the vicinity of the wall as well as smaller velocity in the bulk flow region, which produced better performance of heat transfer with a relatively low friction penalty. The EHTT could obtain 3.3 times higher performance than bare tube, based on the cases studied. It was also shown that Nusselt number increased as the Reynolds number increased, and the EHTT performed better with a larger bottom diameter and smaller pitch of the conical frustums. Surprisingly, for the frustums in which the ratio between the bottom diameter and tube diameter was 0.8, it was indicated that the Nusselt number increased significantly with a slight friction decrease when the ratio between the pitch and tube diameter decreased from 3 to 2.5. This study provides a new insight into heat transfer enhancement and tube configuration, which has a wide engineering application potential.