Thermal efficiency enhancement of nanofluid-based parabolic trough collectors

  • Evangelos Bellos
  • Christos Tzivanidis


The use of nanofluids in parabolic trough collectors is one of the most promising techniques for enhancing their performance. The objective of this work is to investigate the use of various nanoparticles (Cu, CuO, Fe2O3, TiO2, Al2O3 and SiO2) dispersed in thermal oil (Syltherm 800). A detailed parametric analysis is performed for flow rates from 50 to 300 L min−1, for inlet temperatures from 300 K to 650 K and for nanoparticle concentrations up to 6%, while the impact of the solar irradiation level on the thermal efficiency enhancement is also investigated. Moreover, a new index for the working fluid evaluation in solar collectors is introduced. The analysis is conducted with a developed thermal model in Engineering Equation Solver. According to the final results, the most efficient nanoparticle is the Cu, with CuO, Fe2O3, TiO2, Al2O3 and SiO2 to follow, respectively. It is found that the higher enhancement is observed for lower flow rates, higher inlet temperatures and higher nanoparticle concentrations, while it is approximately constant for the different solar irradiation levels. For the typical operating conditions with 150 L min−1 flow rate and 600 K inlet temperature, the thermal efficiency enhancement is found 0.31, 0.54 and 0.74% for Cu concentrations 2, 4 and 6%, respectively.


Solar energy Nanofluid Parabolic trough collector Thermal efficiency Enhancement 

List of symbols


Area, m2


Concentration ratio


Specific heat capacity under constant pressure, J kg−1 K−1


Diameter, m


Focal length, m


Solar direct beam irradiation, W m−2


Heat transfer coefficient, W m−2 K−1


Convection coefficient between cover and ambient, W m−2 K−1


Thermal conductivity, W m−1 K−1


Incident angle modifier


Tube length, m


Mass flow rate, kg s−1


Nusselt number


Prandtl number


Heat flux, W


Reynolds number


Temperature, K


Sky temperature, K


Overall heat transfer coefficient, W m−2 K−1


Volumetric flow rate, L min−1


Ambient air velocity, m s−1


Width, m

Greek symbols


Absorber absorbance


Ratio of the nanolayer thickness to the original particle radius


Intercept factor




Optical efficiency


Thermal efficiency


Solar beam incident angle, o


Dynamic viscosity, Pa s


Density, kg m−3


Mirror reflectance


Cover transmittance


Nanoparticle, concentration %

Subscripts and superscripts






Base fluid




Inner cover


Outer cover


Mean fluid




Thermal loss










Inner receiver


Outer receiver









Computation fluid dynamic


Engineering equation solver


Parabolic trough collector



Dr. Evangelos Bellos would like to thank “Bodossaki Foundation” for its financial support.


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Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2018

Authors and Affiliations

  1. 1.Thermal Department, School of Mechanical EngineeringNational Technical University of AthensAthensGreece

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