Numerical studies on thermo-hydraulic characteristics of laminar flow in a heat exchanger tube fitted with vortex rods

An analysis of the thermo-hydraulic characteristics of a heat exchanger tube fitted with a novel vortex rod insert has been conducted numerically under uniform heat flux conditions. The vortex rods had three relative rod length ratios (LR = b/D = 0.15, 0.25, and 0.35) and three relative rod pitch ratios (PR = p/D = 1, 1.5, and 2), and they were studied for numerous Reynolds numbers (Re) that ranged from 300 to 1800 using water as the working fluid. With these vortex rods, longitudinal swirling (or vortex) flow can be generated for better fluid mixing between the wall and core flow regions, thereby allowing for a high heat transfer rate with a moderate increase in the pressure drop. The results indicate that the presence of the vortex rods elicits a considerable heat transfer enhancement in the tube, Nu/Nu(0) = 1.1-3.9, with an increase in pressure drop, and f/f(0) = 1.4-53. Both the Nu/Nuo and the f/f(0) ratios increase with Re and LR increases and with PR decreases. The performance evaluation criterion (PEC) values of all vortex rod cases are above unity except for the cases with LR 0.15 at Re = 300. The case at which LR = 0.35 and PR = 1 provides the maximum PEC value of approximately 2.22 at Re = 1800. These results provide evidence that the vortex rod insert is a promising technique for laminar convection heat transfer enhancement. (C) 2015 Elsevier Masson SAS. All rights reserved.