Enhancement of heat transfer in solar collectors by vortex generation

ABSTRACT

The importance of solar energy is evident by considering running out of fossil fuel resources and the growing energy demand. The clean and worldwide source of the sun can be a crucial remedy for the energy crisis throughout the world by extracting renewable and CO₂-free solar energy. Solar air heaters are the most common type of heat exchanger for various aspects of solar energy. The conventional type of solar air heaters suffers from low thermal performance. In the current numerical study, some novel geometries are introduced for improving the thermal performance of the air heaters with a highly turbulent flow by borrowing the vortex cooling concept in gas turbine blades. The parameters of Nusselt number, friction factor, and effective efficiency are investigated. The results show a higher heat transfer for the current configurations in comparison to those examined and simulated in the literature. It is such that a minimum 400% increment in the Nusselt number can be obtained compared to that of the simple channel of absorber plate. The efficiency values reveal that the proposed configurations are more economically efficient compared to traditional solar air heaters, especially in the lower Reynolds number, by an increment of about 25%.

KEYWORDS:

• Solar air heater
• vortex cooling of gas turbine blades
• Nusselt number
• friction factor
• heat transfer enhancement

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Acknowledgments

The authors would like to thank the University of Kashan to support this work under Grant No. 1073239.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Nomenclature

$D_h$	=	Hydrodynamic diameter (m)
f	=	Friction factor (-)
G	=	Generation term in turbulence model ($\mathrm{k}\mathrm{g}{\mathrm{m}}^3/{\mathrm{s}}^5$)
h	=	Convective heat coefficient ($\mathrm{W}/\mathrm{K}{\mathrm{m}}^2$)
I	=	Solar radiation intensity ($\mathrm{W}/{\mathrm{m}}^2$)
k	=	Turbulent kinetic energy (${\mathrm{m}}^2/{\mathrm{s}}^2$)
Nu	=	Average Nusselt number (-)
p	=	Pressure (Pa)
Pr	=	Prandtl number (-)
$P_m$	=	Mechanical power for flow (W)
Q	=	Volumetric flow rate (${\mathrm{m}}^3/s$)
$q_u$	=	Thermal power gained (W)
Re	=	Reynolds number (-)
T	=	Temperature (°C)
u	=	Velocity (m/s)
x	=	Dimensional coordinates (m)
Y	=	Dissipation term in turbulence model ($\mathrm{k}\mathrm{g}{\mathrm{m}}^3/{\mathrm{s}}^5$)

Additional information

Funding

This work was supported by the University of Kashan; [1073239].