Thermo-hydraulic performance enhancement of a solar air heater using rotating cylindrical turbulators

Abstract

A novel concept of rotating cylindrical ribs as artificial roughness in a solar air heater to enhance its thermo-hydraulic performance factor has been investigated using 3D computational fluid dynamics. The rotational speed is varied from 2000 RPM to 10000 RPM on the static ribs optimised for height (e), diameter (d), longitudinal pitch (P), and transverse pitch (S) at Reynolds number (Re) ranging from 5000 to 24000. The optimised static ribs configuration having e=3.5 mm, d=3 mm, S=20 mm, and P/e=10 is experimentally validated to establish the accuracy of rotating ribs performance computed using computational fluid dynamics. The maximum thermo-hydraulic performance factor of 1.89 is achieved—32 % higher than the best performance for static ribs—using rotational ribs for the rotational speed of 10000 RPM at Re=5000. A comparison between parallel and perpendicular orientations of rotating ribs with respect to the absorber plate establishes that perpendicular ribs configuration is highly desirable to reduce the pressure drop penalty, in turn, enhancing the thermo-hydraulic performance. The performances of the proposed perpendicularly oriented rotating cylindrical ribs are also compared with the performances reported in the literature for static ribs of different shapes having the same orientation with respect to absorber plate and it is observed that rotational ribs outperforms all the other static ribs.