Convective thermal-hydraulic performance in twisted tubes: From the perspective of symmetrical cross-sectional shapes

To explore the impact of intersecting surface shape on the thermal-fluid behaviors in the twisted tube (TT) under the two conditions of equal area and equal perimeter of intersecting surfaces, a 3D simulation method is used to examine the convection heat transfer characteristics of fluids with different viscosities in TTs with typical symmetrical cross sections at low Reynolds number (Re) according to experimental verification. The results manifest that the regularly helical deformation of the TTs induces secondary flows in the perpendicular direction of the main flow, leading to a better convection heat transfer performance. In the Re range of 650– 1550 with water, the twisted triangular tube produced with equal cross-sectional perimeter exhibits the topmost convection heat transfer performance, with a comprehensive performance evaluation factor of heat transfer (PEF) of 1.85– 1.87. As for the equal cross-sectional perimeters with engine oil, the twisted elliptical tube shows the highest PEF of 1.39– 1.40 as the Re is below 1100. When the Re exceeds 1100, the twisted triangular tube displays the supreme PEF of 1.33– 1.37. For the equal cross-sectional areas with water and engine oil, the twisted elliptical tube presents the utmost PEF of 1.32– 1.47.