Nanofluids in Solar Thermal Collectors: Review and Limitations
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Nanofluids in Solar Thermal Collectors: Review and Limitations Ifeoluwa Wole‑osho1 · Eric C. Okonkwo1,2 · Serkan Abbasoglu1 · Doga Kavaz3 Received: 13 June 2020 / Accepted: 10 September 2020 © The Author(s) 2020
Abstract Solar thermal collectors are systems that allow for the use of solar energy in thermal applications. These collectors utilize a heat transfer fluid to transport absorbed solar radiation to applications where they are needed. Scientists in a bid to improve the conversion efficiency of solar collectors have suggested different collector designs and improved collector materials. Over the last 25 years, the study of nanofluids and their applications have revolutionized material science, and nanotechnology has found applications in improving solar collector materials. This article reviews the impact of different nanomaterials on the efficiency of solar collectors. The study also outlines the limitations of applying nanofluids and discusses the long-term challenges of their application to solar collectors. Nanofluids have the potential to improve the overall efficiency of most solar collectors, however, the full potential of nanofluids in heat transfer applications cannot be completely achieved until some of the questions regarding hysteresis, stability, and the overall predictability of nanofluids are answered. Keywords Compound parabolic collector · Evacuated tube collector · Flat plate collector · Nanofluid · Parabolic trough collector · Solar collector Abbreviations ASHRAE American Society of Heating, Refrigeration and Air Condition Engineers ASTM American Society for Testing and Materials Conc Concentration CPC Compound parabolic collector * Eric C. Okonkwo [email protected] 1
Department of Energy Systems Engineering, Cyprus International University, Nicosia, North Cyprus, Turkey
2
Division of Sustainable Development, College of Science and Engineering, Hamad Bin Khalifa University, Qatar Foundation, Education City, Doha, Qatar
3
Department of Bioengineering, Cyprus International University, Nicosia, North Cyprus, Turkey
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International Journal of Thermophysics
ETC Evacuated tube collector FPC Flat plate collector HTF Heat transfer fluid PTC Parabolic through collector: SEM Scanning electron microscope STC Solar thermal collectors XRD X-ray diffraction Vol Volume List of Symbols A Area (m2) Al Aperture of area (m2) At Area of surface (m2) c Speed of light Cp Specific heat capacity (kJ·kg−1·K) Cr Concentration ratio d Distance D Diameter (m) Di Inlet diameter (m) E Energy (J) Eg Stefan–Boltzmann constant f Wavelength f Friction factor F’ Collector efficiency FR Heat removal factor g Acceleration due to gravity G Direct normal irradiance (W·m-2) I Current (A) h Heat transfer coefficient (W·m-2·K) Hz Hertz k Thermal conductivity (W·m−1·K) L Length (m) m Mass flow rate (kg·min−1) m Mass N Number of glass cover Nu Nusselt number P Pressure Pr Prandtl number Qu Useful energy Q Heat flux (W) Re Reynold
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