Preparation of highly dispersed nanofluid and CFD study of its utilization in a concentrating PV/T system

Abstract In this research, highly dispersed silica/water nanofluids of various particle sizes were successfully prepared using a facile one step sol–gel process. Nanofluids with particle sizes of 5 nm, 10 nm, 25 nm and 50 nm were confirmed by electron microscopy and light-scattering technique. The transmittance and thermal conductivity of the prepared nanofluids were measured. Our results showed that the transmittance of nanofluid with particle size of 5 nm and volume fraction of 2% can be as high as 97%, very close to pure water. Meanwhile, the thermal conductivity for this nanofluid showed ca. 20% enhancement. The good transmittance and high thermal conductivity of the prepared nanofluid enable us to de-couple the photovoltaic (PV) and thermal systems so that each can operate at an optimum temperature. In our design, the infrared part of the concentrated light, which cannot be converted to electricity by PV cell, was absorbed by nanofluid before arriving at PV cell surface. The additional heat generated by PV cell upon electivity generation could be removed by nanofluid flowing below it. The designed PV/T system was reduced to a 2-dimension (2D) physical model and numerically studied by CFD. This design is helpful to reduce the operation temperature of PV cell and thus is expected to improve its photoelectric efficiency. Exergetic efficiencies for PV/T model with various light concentrations versus the velocities of the nanofluid flow were investigated. When the concentration is 40 and the flow velocity is 0.015 m/s, the PV/T system has the highest exergetic efficiency and an enhancement of 7.0% exergetic efficiency was obtained by using nanofluid compared to using DI water. When the concentration is 100 and at the flow velocity of 0.1 m/s, an exergetic efficiency enhancement of 9.5% can be obtained. Considering the practical application of PV/T system, economic flow rate and low cost concentration are always favored. Concentration of 40 at flow velocity of 0.015 m/s was concluded to be the optimal operation parameters for our designed PV/T model using SiO 2 /water nanofluid (5 nm, 2 v%) as working fluid.

[1]  Wu Yuting.  Thermal and power characteristics of ordinary solar cells in concentrating solar collectors , 2003 .

[2]  Shafiqur Rehman,et al.  Performance evaluation of a PV (photovoltaic) module by back surface water cooling for hot climatic conditions , 2013 .

[3]  Somchai Wongwises,et al.  A critical review of convective heat transfer of nanofluids , 2007 .

[4]  Liejin Guo,et al.  Concentrating PV/T Hybrid System for Simultaneous Electricity and Usable Heat Generation: A Review , 2012 .

[5]  Seok Pil Jang,et al.  Effective viscosities and thermal conductivities of aqueous nanofluids containing low volume concentrations of Al2O3 nanoparticles , 2008 .

[6]  Todd Otanicar,et al.  Photovoltaic/thermal system performance utilizing thin film and nanoparticle dispersion based optical filters , 2013 .

[7]  Shang-Liang Chen,et al.  Theoretical and experimental investigations of a two-phase thermosyphon solar water heater , 2011 .

[8]  Haitao Zhu,et al.  Critical Issues in Nanofluids Preparation, Characterization and Thermal Conductivity , 2009 .

[9]  Kamaruzzaman Sopian,et al.  Advances in liquid based photovoltaic/thermal (PV/T) collectors , 2011 .

[10]  T. Yousefi,et al.  An experimental investigation on the effect of Al2O3–H2O nanofluid on the efficiency of flat-plate solar collectors , 2012 .

[11]  Yujin Hwang,et al.  Thermal conductivity and lubrication characteristics of nanofluids , 2006 .

[12]  Tin-Tai Chow,et al.  A Review on Photovoltaic/Thermal Hybrid Solar Technology , 2010, Renewable Energy.

[13]  G. N. Tiwari,et al.  Analytical expression for electrical efficiency of PV/T hybrid air collector , 2009 .

[14]  Feiyu Kang,et al.  Sol-Gel-Hydrothermal Synthesis of the Heterostructured - Composite with High-Visible-Light- and Ultraviolet-Light-Induced Photocatalytic Performances , 2012 .

[15]  Liejin Guo,et al.  Photocatalytic Hydrogen Production from Refinery Gas over a Fluidized-Bed Reactor II: Parametric Study , 2013 .

[16]  Ji Jie,et al.  A numerical and experimental study on a heat pipe PV/T system , 2011 .

[17]  Peter Vadasz,et al.  Heat Conduction in Nanofluid Suspensions , 2006 .

[18]  K. F. Fong,et al.  Energy and exergy analysis of photovoltaic-thermal collector with and without glass cover , 2009 .

[19]  P. Schurtenberger,et al.  A new instrument for time-resolved static and dynamic light-scattering experiments in turbid media. , 2009, Journal of colloid and interface science.

[20]  H. Metselaar,et al.  A review of nanofluid stability properties and characterization in stationary conditions , 2011 .

[21]  S. Zeinali Heris,et al.  Numerical Study on Convective Heat Transfer of AL2O3/Water, CuO/Water and Cu/Water Nanofluids through Square Cross-Section Duct in Laminar Flow , 2012 .

[22]  Robert A. Taylor,et al.  Nanofluid-based optical filter optimization for PV/T systems , 2012, Light: Science & Applications.

[23]  Martin A. Green,et al.  Solar cell efficiency tables (version 39) , 2012 .

[24]  T. Yousefi,et al.  An experimental investigation on the effect of MWCNT-H2O nanofluid on the efficiency of flat-plate solar collectors , 2012 .

[25]  O. Glatter,et al.  Dynamic light scattering in turbid nonergodic media. , 2008, The Review of scientific instruments.

[26]  Ha Herbert Zondag,et al.  Flat-plate PV-Thermal collectors and systems : a review , 2008 .

[27]  W. Warta,et al.  Solar cell efficiency tables (Version 45) , 2015 .