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Experimental study on the effect of bio-functionalized graphene nanoplatelets on the thermal performance of liquid flat plate solar collector


Synthesis of carbon-based working fluid involves toxic acids that are hazardous to the human and surrounding environment. In the current experimental investigation, thermal analysis of liquid flat plate solar collector was carried out using distilled water and environmentally friendly, covalent functionalized graphene nanoplatelets. Gallic acid was grafted on GNPs using the green free radical technique. Chemical characterization was analyzed using EDX and FESEM. Colloidal stability of GGNP nanofluids was found to be stable for more than 60 days. GGNPs were dispersed in distilled water with varying mass concentrations from 0.025 to 0.1%, and analysis was carried out for flow rate ranging from 0.5 to 1.5 L min−1 for different heat flux intensities and inlet temperature. The thermal performance of LFP solar collector augments with the surge in GGNP concentration, flow rate and heat flux intensities, whereas declines with the increase in reduced temperature parameter. Maximum thermal efficiency enhancement of 21.48%, 16.06% and 12.36% is achieved using 0.1%, 0.05% and 0.025% GGNP nanofluid than distilled water. A penalty in the form of a slight surge in pressure drop and pumping power was observed with a subsequent increase in GGNP concentration. The maximum increase in pressure drop and pumping power was about 0.85% and 0.567% for 0.1% concentration and mass flow rate 1.5 L min−1. A maximum reduction of about 25% in the size of the LFP solar collector area is attained using 0.1% GGNPs than base fluid.

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\(A_{{\text{c}}}\) :

Aperture area of the solar collector (m2)

AR :

Inner area of the riser tubes (m2)

\(A_{{{\text{RC}}}}\) :

Reduction of size of solar collector (m2)


American Society of Heating, Refrigeration, and Air-Conditioning Engineers


American Society of Mechanical Engineers


Cetyltrimethylammonium bromide

\(C_{{\text{p}}}\) :

Specific heat (J kg1 K1)


Inner diameter (mm)


Energy-dispersive X-ray spectroscopy


Field emission scanning electron microscope

\(F_{{\text{R}}}\) :

Heat removal factor

\(F_{{\text{R}}} \left( {\tau \alpha } \right)\) :

Absorbed energy parameter

\(F_{{\text{R}}} U_{{\text{L}}}\) :

Energy loss parameter


Gum Arabic


Graphene nanoplatelets


Gallic acid graphene nanoplatelets


Heat transfer coefficient (W m2 K1)

\(I_{{\text{T}}}\) :

Heat flux intensity (W m2)

k :

Thermal conductivity (W m1 K1)

L :

Length of the tube (m)


Liquid flat plate

\(\dot{m}\) :

Fluid flow rate (kg s1 or L min1)


Polyethylene glycol—400

\(Q_{{\text{u}}}\) :

Useful heat gain from the solar collector (W)

\(Q_{{{\text{conv}}}}\) :

Power input (W)


Sodium dodecyl benzene sulfonate


Sodium lauryl sulfate



\(T_{{{\text{out}}}}\) :

Outlet temperature of working fluid (K)

\(T_{{{\text{in}}}}\) :

Inlet temperature of working fluid (K)

\(T_{{\text{p}}}\) :

Absorber plate temperature (K)

\(T_{{\text{b}}}\) :

Bulk temperature (K)

\(U_{{\text{L}}}\) :

Overall loss coefficient (W m2 K1

ρ :

Density (kg m3)

µ :

Dynamic viscosity (m Pa. s)

P :

Pressure drop (N/m2)

\(\eta_{{\text{T}}}\) :

Thermal efficiency of LFP solar collector (%)

\(\tau \alpha\) :

Product of transmissivity and absorptivity


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The authors gratefully acknowledge the FRGS Grant FP143-2019A and research Grant GPF019A-2019, IIRG006B-19IISS, University of Malaya, Kuala Lumpur, Malaysia, for the support to conduct this research work.

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Correspondence to L. Harish Kumar or S. N. Kazi.

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Kumar, L.H., Kazi, S.N., Masjuki, H.H. et al. Experimental study on the effect of bio-functionalized graphene nanoplatelets on the thermal performance of liquid flat plate solar collector. J Therm Anal Calorim 147, 1657–1674 (2022).

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