THERMAL-HYDRAULIC OPTIMIZATION OF A SOLAR WATER HEATER THROUGH LONGITUDINAL VORTEX GENERATOR

Resumo

Nowadays, the development of technologies to harness energy from renewable sources as
solar and wind energy has increased a lot, mainly because of concerns about the burning fossil fuel
and the fast growth of the populations. The solar energy is a great alternative to meet the increasing
demand based on cost effectiveness and accessibility compared to other sources. For thermal solar
application, the researchers have been working to enhance the systems to find cheaper process and
higher efficiency. These studies are fundamental in order to promote the use of solar energy for,
among other, communities with financial restrictions, domestic activities and industry that need of
temperature at medium level. The Computational Fluid Dynamic (CFD) and Genetic Algorithm
Methodology have been successfully coupled to optimize an objective function problem related to
enhancement heat transfer of a solar water heater through Longitudinal Vortex Generators (LVG)
which increase the mix between the cold and hot streams near the wall of circular tubes. This passive
technique can improve the heat transfer by changing the flow dynamic and delay the detachment of the
boundary layer. This work aims to find the optimal shape of a stamped vortex generator over a flat
plate inside a circular tube for operating conditions similar those find in Brazil. The parameters of the
longitudinal vortex generator evaluated are the angle of attack, height and length which were
optimized through Genetic Algorithm approach using a commercial software called by ESTECO
ModeFrontier. The heat transfer and the dynamic flow were solved by ANSYS Fluent for Reynolds
number 900. The results show the optimal design of LGV which enhance 62% the heat transfer and
increase 3 times the pressure drop. The velocity and temperature contours show the mix between the
hot and cold streams and the low pressure zones size, besides, the streamlines indicated a corner
vortex presence.