| Nanofluid with excellent thermal and optical properties is gradually used as working media for PV/T system.In present study,the performance of PV/T systems working with different nanofluids with a volume fraction of 1%and using deionized water as base fluid was studied experimentally,including carbon,CuO,Al2O3,SiO2 and graphite nanofluids.Results show that the SiO2 nanofluid has the best solar absorbing property among them attributing to the best performance of PV/T system with a electrical and thermal efficiency of 4.4%and 82.57%,respectively.Although the produced electric power was less than PV system(5.83%)alone,the PV/T system has obtained a large amount of extra heat.According to the experimental research,nanofluid has a great effect on the overall performance of PV/T system.Therefore,we present a thorough investigation on the correlation between solar absorption and the materials,size and geometries of nanoparticles though using the finite-difference time-domain(FDTD)method.Results show that solar absorption power for per unit volume of carbon,graphite and CuO has optimal diameter about 60nm,100nm,160nm respectively,but 20nm,20nm,120nm and 160nm for Sic、Si3N4、TiO2 and ZnO nanoparticles.Fe3O4 have the ability of full-spectrum absorption and have good spectral complementary absorption characteristics.Its optimal absorption diameter from the unit volume is 200nm.The optimal geometry for SiC is cone,but it is cube fo Si3N4、TiO2 and ZnO.Their absorbed power is respectively 2.5、2.4、1.03 and 1.01 higher than that of corresponding sphere nanoparticles with same volume.For Fe3O4 with cone geometry,it has the best light absorption with a value of 4.18×10-12W when the vertex angle is about 103°.Then a new type of composite nanoparticle is proposed,exhibiting an improved solar absorption by nearly 67%compared with the corresponding core-shell structure.Finally,the forces exerted on non-homogeneous or non-spherical nanoparticles under illumination are analyzed,and photophoretic lift force is proposed.The calculation expression of this type of photophoretic force is given by analogy with Magnus lift force and is qualitatively verified. |
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