Heat transfer performances of isosceles triangular cross sectioned wire coils

The heat transfer improvement work continues intensively in parallel with the development of the thermal systems. Since the promotion of heat transfer leads to the provision of energy and cost efficiency, focusing on finding heat transfer enhancement techniques and improve efficiency is demanded. Heat transfer enhancement of air flow using wire coiled of an isosceles triangular cross-section and twisted tape inserted in a tube have been investigated under turbulent flow regime in the range of Reynolds number from 4000 to 20,000. A simulation technique is employed to simulate the swirling flow with three different pitch ratios (P/D = 1, 2, and 3). The isosceles triangle side length to tube diameter (a/D) is 0.2, 0.4, 0.6, 0.8, and 0.93. The distance of twisted tape from the tube wall is 2 mm. The heat transfer enhancement represented by a Nusselt number (Nu) and friction factor (f) in turbulent flow regime under constant heat flux condition with constant inlet temperature are numerically investigated by Ansys FLUENT to understand the physical behaviour of the thermal and fluid flows in the flow field. The results are presented in terms of average Nusselt number, friction factor, velocity contour and turbulent kinetic energy contour. The results show that the use of twisted tape and isosceles coiled wire lead to a considerable increase in heat transfer and pressure drop in comparison with the smooth pipe. The Nusselt number increases with the increase of triangle side length and twist width and with the decrease of pitch ratio. The results indicate that the wire coil with a/D=0.8 comparing to the smooth pipe has provided higher enhancement with average heat transfer enhancement of 153%, 128%, and 112% for TWC4A, TWC4B, and TWC4C, respectively along the range of Reynolds number used in the present study. Nevertheless, the twisted tape with a/D=0.93 improve the heat transfer efficiency to be 147%, 151%, and 143% for T.T5A, T.T5B, and T.T5C, respectively. Also, the wire coil with a/D=0.8 has higher efficiency comparing to the twisted tape and wire coils isosceles triangle cross-section with other ratios.