Heat transfer performance and flow characteristic in enhanced tube with the trapezoidal dimples

Heat transfer and hydrodynamic flow characteristics are examined numerically in a horizontal tube having trapezoidal dimples on surface. Constant heat flux is applied on the outer surface of the tube. Water is selected as working fluid. Investigated parameters of the trapezoid dimples are taken as dimple diameter (D-d = 5, 6 and 7 mm), trapezoid angle (alpha = 30 degrees, 45 degrees and 60 degrees), pitch length of dimples (PL = 10, 20, 30, 40 and 50 mm). The analyses are conducted for both transient and turbulent flow conditions (3000 <= Re <= 8000). The results are presented as Nusselt number (Nu), friction factor (f) and performance evaluation criteria (PEC) versus Reynolds number (Re). The highest Nu is obtained 2.1 times greater than smooth tube for D-d = 7 mm, alpha = 60 degrees, PL = 10 and Re = 8000. The lowest f is obtained 1.39 times greater than smooth tube in case of D-d = 5 mm, alpha = 30 degrees, PL = 50 and Re = 8000. The highest PEC value is obtained as 1.72 in D-d = 7 mm, alpha = 60 degrees, PL = 10 and Re = 3000 case.