An investigation of the thermo-hydraulic performance of the smooth wavy fin-and-elliptical tube heat exchangers utilizing new type vortex generators

摘要

A three-dimensional CFD numerical simulation is successfully carried out on thermo-hydraulic characteristics of a new smooth wavy fin-and-elliptical tube (SWFET) heat exchanger with three new types of vortex generators (VGs), namely - rectangular trapezoidal winglet (RTW), angle rectangular winglet (ARW) and curved angle rectangular winglet (CARW). Several parameters have been examined in this study. There have a pronounced effect on the thermo-hydraulic performance. In addition the results are analyzed from the viewpoint of the field synergy principle which emphasizes that the reduction of the synergy angle between velocity and fluid temperature gradient is the principal mechanism for enhancement of heat transfer performance. These parameters include: Reynolds number (based on the hydraulic diameter, Re-Dh = 500-3000), geometric shape of VGs, attack angle of VGs (alpha(VG) = 15-75 degrees), placement of VG pairs (up- or/and downstream), tube ellipticity ratio (e = 0.65-1.0) and wavy fin height (H = 0.8-1.6 mm). The results demonstrate that with increasing Reynolds number and wavy fin height, decreasing the tube ellipticity ratio, the heat transfer performance of the SWFET heat exchanger is enhanced. The SWFET heat exchanger with the advantages of using CARW VGs and RTW VGs at smaller and larger attack angles, respectively, presents good thermo-hydraulic performance enhancement. Finally, new correlations are proposed to estimate the values of the average Nusselt number Nu, friction factor f and synergy angle theta based on the Reynolds number, attack angle of VGs, tube ellipticity ratio and wavy fin height. (C) 2015 Elsevier Ltd. All rights reserved.