Enhancement of absorptance of absorber surfaces of a flat plate solar collector using black coating with graphene

ABSTRACT

The effect of graphene-based selective coating on the absorber plate of a flat plate solar collector (FPSC) is investigated experimentally. The absorber plate is a mild steel substrate with a mixed coating of graphene and black paint. Three samples are prepared, the different ratios of black paint to graphene being 1:1, 1:2, and 1:3. The average absorptivity of the graphene and black paint coated samples are determined to be about 0.87 and 0.82, respectively. The absorptance capacity of the collector plate surface for shortwave solar radiation is found to increase by about 6.1% due to graphene presence. Real-time experiments are conducted to determine the thermal efficiency of the FPSC using air as the heat transfer fluid. The absorber surface with 1:3 ratio of black paint and graphene coating is observed to have an average thermal efficiency of 36.65% for the airflow rate of 0.2 kg/h, which is about 6.25% more than that of the standard black paint coating because of higher thermal conductivity of graphene particles. The provision of a serpentine path in the absorber plate is useful in eliminating additional absorber tubes or fins.

KEYWORDS:

• Flat plate collector
• graphene coating
• absorptivity
• optical performance
• air heater
• thermal efficiency

Nomenclature

$A_c$	=	Flat plate collector area [${\mathrm{m}}^2]$
${\mathrm{C}}_{\mathrm{p}}$	=	Specific heat of air [J/g.K]
$I_g$	=	Solar radiation intensity [W/m2]
$\text{dotm}$	=	Mass flow rate of HTF [kg/h]
${\mathrm{T}}_{\mathrm{a}}$	=	Ambient air temperatures [°K]
${\mathrm{T}}_{\mathrm{i}}$	=	HTF inlet temperatures of air [°K]
${\mathrm{T}}_{\mathrm{o}}$	=	HTF outlet temperatures of air [°K]
$T_{Sun}$	=	Sun surface temperature [°K]

Greek symbols

$\tau \alpha$	=	Absorptance transmittance product
η	=	Energy efficiency [%]
${ }_{ex}$	=	Exergy efficiency [%]

Abbreviations

FPSC	=	Flat plate solar collector
HTF	=	Heat transfer fluid

Acknowledgments

Authors are grateful to the management of SRM Institute of Science and Technology, Chennai to provide the required research facility.

Declaration of conflicting interests

The authors declare that there is no potential conflict of interest.

Additional information

Funding

This research received no specific grant from any funding agency.

Notes on contributors

Ramalingam Senthil

Ramalingam Senthil is working as Associate Professor at SRM Institute of Science and Technology, Chennai from 2005. He is the author of more than 55 articles in the indexed journals. He is interested in renewable and sustainable energy. He is a member of professional bodies, namely ISES, SESI, FIE, ISTE, etc.

K. Kishore Kumar

K. Kishore Kumar has completed his B. Tech in Mechanical engineering from SRM Institute of Science and Technology. He is interested in wind energy, solar energy and other sustainable energy resources. He is aiming to build an energy efficient society with new scientific approaches.

Kodak Rohan Rajendra

Kodak Rohan Rajendra has completed his B. Tech in Mechanical engineering from SRM Institute of science and technology. He is interested in HVAC field, solar energy and its utilization and also the Automobile sector. He is a technology driven Engineer with constant efforts to develop the surrounding with the newly upgraded technology.

Aniyush Juneja

Mr. Aniyush Juneja has completed his B. Tech in Mechanical engineering from SRM Institute of science and technology. He is interested in renewable energy and efficient energy collection, storage and utilization. He is interested to develop the environmentally friendly energy solutions to the society.