Study on heat transfer characteristics of a circular tube with polygonal twisted elements

This paper reported experimental and numerical simulation investigations on heat transfer characteristics of polygonal twisted elements in the constant wall temperature with Reynolds number (Re) ranging from 200 to 1800. In this study, the results revealed that the entransy efficiency (eta) increased with the polygonal twisted element's edge number increasing. Moreover, the highest entransy efficiency eta of the quadruple-edge continuous twisted element (QEC) heat exchange tube was 93.97%. Besides, the field synergy performance also showed a positive correlation with the element edge number. A maximum increase of 57% was observed in the field synergy number (Fc) of the QEC insert as compared with the plain tube while the performance evaluation criteria (PEC) had little relationship with the element edge number. In the case of the interlaced twisted elements, both the PEC value and the entransy efficiency eta were lower than the corresponding continuous ones. In addition, the Fc values were not apparent, of which the maximum difference was only 7% in the two cases(continuous twisted element and interlaced twisted element). In Re= 1800, when the d/D(the ratio of the twisted element diameter to the inner diameter of the tube) of the QEC heat exchange tube increased, the PEC values and Fc values both increased significantly. The maximum PEC value was 1.62 and the maximum Fc values was 202% higher than the plain tube. Subsequently, the entransy efficiency eta got the maximum value in the range of d/D = 0.375-0.75. The maximum entransy efficiency was 91.07%.