Modeling the Turbulent Flow and Heat Transfer in a Vertical U-Tube
In this work, three-dimensional incompressible turbulent flow and heat transfer in a circular tube of U-configuration has been investigated numerically. The influences using the vertical U-tube in various curvature radius ratios on thermal and hydrodynamic fields are presented in details. The case for U-tube is tested by using the tube with different curvature radius ratios (1, 1.5 and 2). The tube surface is subjected to a constant heat flux and the air is chosen to be the working fluid with turbulent flow under a range of Re. Number (10000 to 25000). The turbulent flow and heat transfer is governed by continuity, momentum and energy equations. The effect of turbulence is treated by a k-? turbulent model. ANSYS fluent code (15.0) based on finite volume method is used to get the numerical results.
The obtained results of reducing the curvature radius ratio show an increasing in both Nusselt-number and friction factor as compared with those of direct tube, for all the considered values of Re. Number. It is discovered that reducing the curvature radius ratio by 100% enhance the heat transfer by about 5%, due to the strong intensification of the secondary flows.The optimum enhancement efficiency is ranged between 1.07 to 1.099 for using the circular cross-section U-tube, with Rc=1. The present numerical results are compared with empirical correlations and verified a comparatively good agreement.