Convective heat transfer enhancement mechanisms in circular tube inserted with a type of twined coil

Abstract

Abstract Numerical method is used to investigate convective heat transfer enhancement mechanisms in a tube with a new kind of twined coil insert. The numerical results are examined by the experiments specially designed. The heat transfer performance of the tube with the twined coil insert is evaluated in thermal performance factor JF at identical mass flow rate. The heat transfer enhancement mechanisms of the twined coil insert are discussed. It is found that the twined coil insert can make fluid flow be complicated three-dimensional mixed flow, and increase the intensity of secondary flow greatly. These factors can enhance mixing of fluids having different temperature, and then the heat transfer performance in the tube is enhanced. Under the same working conditions, the heat transfer ability of the tube with twined coil insert are much higher than that of smooth tube. The ratio of Nusselt numbers of the tubes with and without insert is about 12.0-38.2, while the ratio of the friction factors of the tubes with and without insert is 7.7-18.1, when Reynolds number Re ranges from 400 to 1800. The maximum thermal performance factor JF can reach 2.16 at Re=1000. Correlations of Nusselt number Nu and the friction factor f with Re are presented.