A Numerical Study on Fluid Flow and Heat Transfer Performance of Internally Roughened Tubes with Dimples

Abstract

In this paper, 3D numerical simulations are conducted in heat transfer enhanced tubes with internally roughened dimples in the range of Re = 2000 to 11,000. The fluid flow and heat transfer characteristics are fully understood by the local and overall friction factors, Nusselt number, and Colburn j factor. The local mean friction factor has a periodic change due to the periodic dimple distribution, the eddy zone and high-pressure region of every dimple greatly influence the working fluid for heat transfer enhancement. In this numerical simulation, five samples are employed to study the detailed heat transfer characteristics. The results show that the dimpled tube is a new kind of heat transfer enhanced tube with the excellent heat transfer performance and low resistance. It is found that the effects of dimples on the heat transfer performance can be well described by the field synergy principle. The effect of different dimple arrangements is very little, which is always within 2%. But the effect of dimple size on heat transfer and fluid flow performance is very significant, thus there exists a tube with an optimum dimple size among the tubes investigated in this paper. By integrated performance evaluation of Nuf0/Nu0f, a maximum of about 60% heat transfer enhancement with the same friction penalty can be gained by the optimal dimpled tube.