Longitudinal vortex generator applied to heat transfer enhancement of a flat plate solar water heater

• Published in: Applied thermal engineering 2019-07, Vol.158, p.113790, Article 113790
• Main Authors: da Silva, Felipe A.S., Dezan, Daniel J., Pantaleão, Aluisio V., Salviano, Leandro O.
• Format: Article
• Language: English
• Subjects: Angle of attack; Circular tubes; Computational fluid dynamics; Delta wings; Flat plates; Fluid flow; Friction factor; Generators; Heat exchangers; Heat transfer; Heat transfer enhancement; Industrial development; Inserts; Longitudinal vortex generator; Population growth; Pressure drop; Reynolds number; Secondary flow; Solar collectors; Solar energy; Solar energy conversion; Solar water collector; Thermal energy; Vortex generators; Vortices; Working fluids
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2019.113790

•Longitudinal vortex generator is effective to enhance the heat transfer in a solar water heater.•Vortex generator shape and angle of attack impact on the heat transfer more than Reynolds number.•The main and corner vortex is the main thermal-hydraulic phenomenology.•The asymmetrical plate is not effective to enhance the heat transfer.•The ratio between heat transfer and pressure drop penalty is higher for delta-winglet vortex generator. The population growth and industrial development increase the demand for energy and the solar energy conversion is an important alternative to complement the world energy matrix. Flat plate solar collectors are devices that convert the solar energy into thermal energy and store the thermal energy in a working fluid, which could reduce the required electricity to heat water. However, an increase in the heat transfer in this type of equipment remains a great challenge. In the current research, two types of longitudinal vortex generators are placed into circular tube of a solar collector in order to enhance the heat transfer between tube walls and working fluid. The numerical modeling is performed by ANSYS 18.0 software and the flow pattern and heat transfer characteristics are analyzed in details for two types of vortex generators (delta-winglet and rectangular-winglet), Reynolds number of 300, 600 and 900, and angle of attack of 15°, 30° and 45°. Ten vortex generators were uniformly arranged on a flat-plate inside the tube. The results show that the delta-winglet and rectangular-winglet longitudinal vortex generators are in fact a passive technique capable to enhance the heat transfer in a solar water heater. The highest heat transfer is obtained for attack of the angle of 45° for both vortex generators, which is more pronounced for the rectangular-winglet vortex generator. However, the best ratio between the heat transfer and the pressure drop penalty is achieved for the delta-winglet vortex generator for angle of attack of 30°. The secondary flow is successfully generated by the inserts, although the corner vortex is observed only by rectangular-winglet vortex generator. Finally, the first vortex generator only impacts on the friction factor and can be removed with no significant losses on the heat transfer.