Heat transfer enhancement for spiral finned tubes with triangular winglets

Abstract

Spiral finned tube (SFT) has been widely used in various applications, including heat exchangers in power plants and metallurgy, energy and chemical industries because of their compact design and ease of production. This study aims to enhance and optimise heat transfer and decrease the flow resistance of SFTs in heat exchangers, which could help reduce manufacturing costs and fuel consumption. In this study, a mathematical model of heat transfer coupling with the fluid and solid components of SFTs is established, and the flow field of SFTs is experimentally verified by particle image velocimetry. To improve the heat transfer over the air side, triangular winglets are built by stacking evenly spaced on the surface of SFTs. The heat and flow characteristics are numerically computed using large-eddy simulation in the same way as the experimental model, and these SFTs are compared with ordinary spiral fin tubes (OSF) at Reynolds numbers ranging from 500 to 9000. The influence of the location and deployment of the triangular winglets is also investigated for performance improvement. On this basis, the heat transfer and resistance of sixteen different SFTs are calculated using an orthogonal experimental design method, In addition, the correlations between the Nusselt (Nu) number and fanning friction coefficient (f) of an optimised model are presented. The results show that SFTs with triangular winglets exhibit significant performance compared with OSFs. The heat transfer coefficient also improves as the number of triangular winglets increases. The optimised model exhibits good accuracy above 95% in terms of the correlation between heat transfer and fanning frictional coefficient.