An investigation of the thermo-hydraulic performance of the smooth wavy fin-and-elliptical tube heat exchangers utilizing new type vortex generators. (15th January 2016)

• Record Type: Journal Article
• Authors: Lotfi, Babak; Sundén, Bengt; Wang, Qiuwang
• Is Part Of: Applied energy. Volume 162(2016)
• Page Start: 1282
• Page End: 1302
• Publication Date: 2016-01-15
• Subjects: Smooth wavy fin-and-elliptical tube heat exchanger -- Vortex generators -- Thermo-hydraulic performance -- Field synergy principle -- 3D CFD numerical simulation; Power (Mechanics) -- Periodicals; Energy conservation -- Periodicals; Energy conversion -- Periodicals; 621.042
• DOI: 10.1016/j.apenergy.2015.07.065
• Languages: English
• ISSNs: 0306-2619

Abstract

Highlights: The present study aims to develop a new shape of vortex generator. 3D simulation on a SWFET heat exchanger with new VGs was conducted. The CARW VGs can enhance thermo-hydraulic performance at small attack angles. The field synergy principle was used to explore heat transfer enhancement mechanism. The influence of six geometrical parameters was evaluated. Abstract: 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 D h = 500 – 3000 ), geometric shape of VGs, attack angle of VGs ( αVG = 15–75°), 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 θ based on the Reynolds number, attack angle of VGs, tube ellipticity ratio and wavy fin height.