Numerical Study of the Effect of Grashof Number on the Mixed Convection Heat Transfer of Laminar Flow in Horizontal Curved Enhanced Heat Transfer Vipertex Tube

Thermal and hydrodynamic behavior of a laminar flow of water within a horizontal curved Vipertex tube with mixed convection heat transfer, in the range of low Grashof numbers, has been numerically studied. The curved horizontal Vipertex tube has geometry of 180o, fixed radius of centerline curvature of 2R/D=6.62, roughness height e/D=0.1, and a constant heat flux is exerted on the walls. The three-dimensional governing equations were using a finite volume method. To solve the problem, the computational fluid dynamics of ANSYS Fluent The results reveal that not only Grashof number and the buoyancy forces arising from it, but the mutual effects of the centrifugal and the buoyancy forces affect the thermal and hydrodynamic characteristics such as axial velocity contours, secondary flow vectors, temperature contours, heat transfer coefficient, and skin friction coefficient. So that, for a given Reynolds number, increasing due to more interaction between buoyancy and centrifugal forces, results in the Vipertex tube. Therefore, the buoyancy forces decrease and lead to the lower heat transfer coefficient, but in smooth curved Grashof number leads to the higher heat transfer coefficient. Nevertheless, the Vipertex curved tube in of Grashof and Reynolds, in each Grashof and Reynolds equally, has a higher heat transfer than a smooth curved pipe. The results also indicated that the skin friction coefficient in these types of tubes can be up to 3.5 times higher than that of smooth one with a Grashof increase.