Thermal performance optimization of rectangular cavity receiver for cross linear concentrating solar power system

ABSTRACT

A thermodynamic analysis was performed on a newly developed concentrated solar power (CSP) technology known as the Cross-Linear (CL), which addresses the issue of cosine loss in conventional CSP technology. The analytical model has been developed and validated using experimental data collected at the experimental site situated in Bhopal, India. The analysis was performed under direct normal irradiance of 775 W/m² with the key objective to determine the optimum inlet condition of the heat transfer fluid (HTF) considering three optimization parameters: HTF outlet temperature, energy, and exergy efficiency of the receiver. Also, the exergy of the solar field is investigated depending on the available solar irradiation throughout the day for three different configurations of the heliostat field. After a comprehensive analysis of the results, the optimal air inlet temperature range was observed to be between 373 and 423 K, and the optimal air mass flow rate was overserved to be 0.0925 kg/s (333 kg/h), which provides energy and exergy efficiency values within 50% to 60% and 28% to 34%, respectively. The maximum electrical exergy efficiency for 30 kW plant capacity is observed to be around 70% at solar noon with a cosine factor of around 0.9 for 4-hour duration.

KEYWORDS:

• Cross linear
• concentrated solar power
• energy efficiency
• rectangular cavity receiver
• heliostats
• exergy efficiency

Nomenclature

$I_b$	=	Solar direct beam irradiance (W/m2)
$A_{ap}$	=	Effective aperture area of the reflector (m2)
$A_r$	=	Surface area of the reflectors (m2)
$\dot{m}$	=	Mass flow rate of HTF (kg/s)
$c_p$	=	Specific heat of HTF at constant pressure, (kJ/kg.K)
$T_o$	=	Outlet temperature of HTF
$T_i$	=	Inlet temperature of HTF
$T_r$	=	Absorber tube surface temperature, (K)
$T_{o,ex}$	=	Experimental outlet temperature of HTF,
$T_{o,th,}$	=	Theoretical outlet temperature of HTF,
$T_{o,cfd,}$	=	Numerical (CFD) outlet temperature of HTF, (K)
$Q_{g,1}$	=	Heat gain by fluid from surface 1 (Front), (W)
$Q_{g,2}$	=	Heat gain by fluid from surface 2 (Back), (W)
$h_o$	=	Enthalpy of HTF at outlet, (J/kg)
$h_i$	=	Enthalpy of HTF at inlet, (J/kg)
$D_{t,i}$	=	Internal diameter of tube, (m)
$L$	=	Length of tube or receiver, (m)
$k_f$	=	Thermal conductivity of HTF, (W/m.K)
${\mu }_f$	=	Absolute viscosity of HTF, (Pa-s)
$N_s$	=	Number of reflectors in one mirror line
$N_r$	=	Number of mirror lines
$.\alpha$	=	Absorptivity of tube surface
$\zeta$	=	Glass cover transmissivity
$.\rho$	=	Reflector reflectivity
$\gamma$	=	Intercept factor
$\delta$	=	Declination angle
$\varphi$	=	Latitude angle
$\mu$	=	Elevation angle
$\omega$	=	Hour angle
Abbreviations	=
HTF	=	Heat transfer fluid
CL-CSP	=	Cross linear concentrated solar power
DNI	=	Direct normal irradiance, (W/m2)
CL	=	Cross linear
EES	=	Engineering equation solver
CosEffect	=	CosineEffect

Acknowledgements

The authors would like to acknowledge the faculties of Energy centre, Maulana Azad National Institute of Technology Bhopal for providing the required facilities and guidance for performing this research.

Disclosure statement

No potential conflict of interest was reported by the authors.

Authors’ contributions

A Patel: Conceptualization, Methodology, Writing – original draft preparation, Writing -review and editing, Software, R Malviya: Resources, review and editing, A Soni: Supervision, Validation, P Baredar: Supervision, Validation.

Additional information

Notes on contributors

Akash Patel

Akash Patel is a PhD Research Scholar of Energy centre, Maulana Azad National Institute of Technology (MANIT), Bhopal, India. His research interests includes solar thermal technologies, computational fluid dynamics and optimization of thermal energy systems.

Rajkumar Malviya

Rajkumar Malviya is a PhD Research Scholar of Energy centre, Maulana Azad National Institute of Technology (MANIT), Bhopal, India. His research interests include hybrid solar concentration technologies, solar water pumping systems and Solar PV systems.

Archana Soni

Archana Soni is an Associate Professor in the Energy centre, Maulana Azad National Institute of Technology (MANIT), Bhopal, India. Her research interests includes Energy Audit and conservation, Energy Intensity Analysis, Green Buildings, Energy Storage, Solar PV design.

Prashant Baredar

Prashant Baredar is Professor and Head, Energy centre, Maulana Azad National Institute of Technology (MANIT), Bhopal, India. His research interests includes Thermal Engineering and Integrated Energy Systems.