Arabian Journal for Science and Engineering

, Volume 44, Issue 3, pp 2535–2549 | Cite as

Experimental Validation of Exergy Optimization of a Flat-Plate Solar Collector in a Thermosyphon Solar Water Heater

  • Koholé Yemeli WenceslasEmail author
  • Tchuen Ghislain
Research Article - Systems Engineering


In this paper, a flat-plate solar collector used in thermosyphon solar water heater has been optimized; and the optimization results used to fabricate a flat-plate solar collector with locally available materials. The constructed heater has then been tested under the climatic conditions of the city of Santa in Cameroon and the measured data used to validate the proposed theoretical model. The computational code that helps to obtain the right combination of the design parameters that maximizes the exergy efficiency was written employing the genetic algorithm. The optimization results show the ability of the heater to achieve high performances with lower surface area of the collector. The experimental and numerical simulation results of a chosen day have been confronted, and the concordance proves to be acceptable. It has also been observed that the absorber plate made of aluminum would have the same performance with that made of copper if it thickness is increased up to 0.005 m and that increasing the insulator thickness to approximately 0.05 m leads to a considerable decrease of the heat loss coefficients and consequently to an increase in the efficiencies of the system.


Experimentation Simulation Exergy Flat-plate collector Optimization Water heater 

List of symbols


Collector surface area (\(\hbox {m}^{2}\))

\(C_\mathrm{b} \)

Bond conductance (\(\hbox {W/m }{^{\circ }}\hbox {C}\))

\(C_\mathrm{c} \)

Specific heat capacity of the glass cover (\(\hbox {J}/\hbox {kg } {^{\circ }}\hbox {C}\))

\(C_\mathrm{f} \)

Specific heat capacity of the working fluid (\(\hbox {J}/\hbox {kg } {^{\circ }}\hbox {C}\))

\(C_\mathrm{p} \)

Specific heat capacity of the absorber plate (\(\hbox {J}/\hbox {kg } {^{\circ }}\hbox {C}\))

\(d_\mathrm{i} \)

Absorber tube inner diameter (\(\hbox {m}\))

\(d_\mathrm{o} \)

Absorber tube outer diameter (\(\hbox {m}\))

\(\dot{E}_{\mathrm{xdest}} \)

Destructed exergy rate (\(\hbox {W}\))

\(\dot{E}_{\mathrm{xin}} \)

Inlet exergy rate (\(\hbox {W}\))

\(\dot{E}_{\mathrm{xin,f}} \)

Inlet exergy carried by the working fluid (\(\hbox {W}\))

\(\dot{E}_{\mathrm{xout}} \)

Outlet exergy rate (\(\hbox {W}\))

\(\dot{E}_{\mathrm{xout,f}} \)

Outlet exergy rate carried by the working fluid (\(\hbox {W}\))

\(\dot{E}_{\mathrm{xu}} \)

Useful exergy rate (\(\hbox {W}\))


Fin efficiency factor


Collector efficiency factor

\(F_{\mathrm{R}} \)

Heat removal factor


Gravitational constant (\(\hbox {m}/\hbox {s }^{2}\))


Solar intensity (\(\hbox {W}/\hbox {m}^{2}\))

\(h_{\mathrm{c,p-c}} \)

Convective heat transfer coefficient between the absorber and the cover (\(\hbox {W/m}^{2}{^{\circ }}\hbox {C}\))

\(h_{\mathrm{r,c-s}} \)

Radiative coefficient between the glass cover and the sky (\(\hbox {W/m}^{2}{^{\circ }}\hbox {C}\))

\(h_{\mathrm{r,p-c}} \)

Radiative heat transfer coefficient between the absorber and the cover (\(\hbox {W/m}^{2}{^{\circ }}\hbox {C}\))

\(h_{\mathrm{c,c-a}} \)

Wind convection coefficient (\(\hbox {W/m}^{2}{^{\circ }}\hbox {C}\))

\(h_{\mathrm{c,p-f}} \)

Convective heat transfer coefficient in the tube (\(\hbox {W/m}^{2}{^{\circ }}\hbox {C}\))

\(k_\mathrm{a} \)

Air layer between absorber plate and glass thermal conductivity (\(\hbox {W/m}{^{\circ }}\hbox {C}\))

\(k_\mathrm{i} \)

Thermal conductivity of the insulation (\(\hbox {W/m}{^{\circ }}\hbox {C}\))

\(l_\mathrm{a} \)

Distance between absorber plate and glass cover (\(\hbox {m}\))

\(\dot{m}_\mathrm{f} \)

Mass flow rate in the collector (\(\hbox {kg/s}\))


Number of glass cover

\(N_{u} \)

Nusselt number

\(n_\mathrm{t} \)

Number of absorber tube

\(P_\mathrm{r} \)

Prandtl number

\(Q_\mathrm{u} \)

Collector useful energy (W)

\(R_\mathrm{a} \)

Rayleigh number

\(T_\mathrm{a} \)

Ambient temperature (\({^{\circ }}\hbox {C}\))

\(T_\mathrm{c} \)

Glass cover temperature (\({^{\circ }}\hbox {C}\))

\(T_\mathrm{f} \)

Working fluid temperature (\({^{\circ }}\hbox {C}\))

\(T_{\mathrm{fi}} \)

Inlet water temperature (\({^{\circ }}\hbox {C}\))

\(T_{\mathrm{fo}} \)

Outlet water temperature (\({^{\circ }}\hbox {C}\))

\(T_\mathrm{p} \)

Absorber plate temperature (\({^{\circ }}\hbox {C}\))

\(T_\mathrm{s} \)

Apparent sun temperature (\({^{\circ }}\hbox {C}\))


time (h)

\(U_\mathrm{L} \)

Overall heat loss coefficient (\(\hbox {W/m}^{2}{^{\circ }}\hbox {C}\))


Wind speed (m/s)


Space coordinate


Center to center distance between absorber tubes (m)

Greek symbols

\(\alpha _\mathrm{c} \)

Absorptivity of the glass cover

\(\alpha _\mathrm{p} \)

Absorptivity of the absorber plate

\(\beta \)

Collector inclination angle (\({^{\circ }}\))

\({\beta }'\)

Volumetric coefficient of expansion

\(\delta _\mathrm{c} \)

Glass cover thickness (m)

\(\delta _\mathrm{i} \)

Insulator thickness (m)

\(\delta _\mathrm{p} \)

Absorber plate thickness (m)

\(\varepsilon _\mathrm{c} \)

Glass cover emissivity

\(\varepsilon _\mathrm{p} \)

Absorber plate emissivity

\(\eta _{\mathrm{en}} \)

Energy efficiency

\(\eta _{\mathrm{ex}} \)

Exergy efficiency

\(\rho _\mathrm{c} \)

Glass cover density (\(\hbox {kg/m}^{3}\))

\(\rho _\mathrm{f} \)

Working fluid density (\(\hbox {kg/m}^{3}\))

\(\rho _\mathrm{p} \)

Absorber plate density (\(\hbox {kg/m}^{3}\))

\(\sigma \)

Stefan–Boltzmann constant (\(\hbox {W/m}^{2}{^{\circ }}\hbox {C}^{4}\))

\(\upsilon \)

Kinematic viscosity (\(\hbox {m}^{2}/\hbox {s}\))

\(\tau _{\mathrm{c}}\)

Glass cover transmissivity


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Copyright information

© King Fahd University of Petroleum & Minerals 2018

Authors and Affiliations

  1. 1.LISIE, Department of Energetic, Environment and Thermal Engineering, IUT-FV BandjounUniversity of DschangDschangCameroon
  2. 2.L2MSP, Department of Physics, Faculty of ScienceUniversity of DschangDschangCameroon

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