| Traditionally,solar thermal utilization represents the majority of global installed capacity of solar energy.As an important part of thermal utilization,solar collectors determine the effectiveness and efficiency of solar energy utilization directly.The direct absorption collector has a unique function in the utilization of solar energy,and can rely on the direct absorption of sunlight by the liquid inside the collector to achieve the photo-thermal conversion.Therefore,it is considered to have higher efficiency than traditional surface absorption collectors,and the optical and thermo-physical properties of the liquid medium have become an important basis for liquid selection.The plasmon resonance effect excited by the surface of noble metal nanoparticles can effectively enhance the photo-thermal conversion performance of the fluid working fluid,and is widely used in the field of solar thermal utilization.In addition,the photo-thermal conversion performance of the fluid can be further enhanced by adjusting the structure of plasmon nanoparticles.This thesis is concentrated on Ag-based plasmon nanoparticles,by changing the nanoparticle structure,size and particle concentration in the target wavelength range,the optical absorption and photothermal conversion characteristics of nanofluids can be adjusted.The main contents are summarized as:?1?By using chemical synthesis methods,the Ag@SiO2 core-shell structure and Au-Ag composite structure?core-shell and dual?plasmon nanofluids were prepared.The absorbance and spectral transmittance of nanofluids of different mass concentration were measured by a spectrophotometer.In the wavelength range of visible light,the optical absorption performance of nanofluids was enhanced with the increase of mass concentration,and there existed a significant plasmon absorption peak.The solar absorption fraction of the nanofluid in the wavelength range of 300-900 nm was analyzed,and it was found that the solar absorption fraction of the working fluid increased with the increase of the incident optical path.?2?Photo-thermal conversion experiments with respect to nanofluids were performed,it was found that the temperature of the fluid increased with the increase of irradiation time.For Ag@SiO2 nanofluids,as the mass concentration of nanoparticles increased,the photothermal conversion performance was enhanced initially and then decreased.There exited an optimal concentration with respect to the best photothermal conversion performance of nanofluids.After the photo-thermal conversion experiment,the temperature of Ag@SiO2 nanofluid at 125 ppm concentration increased from room temperature to 71.1?.It was 9.6?higher than that of deionized water,and the collection efficiency also increased by 18.9%.As for Au-Ag composite structure nanofluids,after the photo-thermal test,the maximum temperature was 15?higher than that of water,and the collection efficiency was increased by 56.9%.?3?The optical absorption properties of the core-shell structure and the Janus structure Au-Ag nanofluid were compared.Owing to the multi-excited plasmon mode of the Janus structure,its optical absorption in the 600-700 nm spectral range was superior to the core-shell structure nanofluids.Comparing the results of the photo-thermal conversion experiments of these two structures of nanofluids,it was found that the temperature rise curves of two structures of Au-Ag nanofluids differed a little.The change of Au-Ag nanostructure were analyzed after the photo-thermal test.The core-shell structured nanofluids have no obvious difference compared with that before the photo-thermal experiment,while the thermal stability of linked ligands with Janus structure decreased during the experiment,resulting in the degradation of photo-thermal conversion performance.?4?Based on Maxwell's electromagnetic wave theory,the finite-difference time-domain method was used to develop the physical model of its dispersion system for Ag@SiO2 and Au@Ag nanofluids.By changing the size of the nanostructure shell layer,core diameter and the dielectric constant of the environmental medium,the effect of the absorption properties of Ag@SiO2 and Au@Ag nanofluids was further investigated.For the nanofluid with core-shell structures,adjust the thickness of the shell,its absorption of incident light increased with the thickness of the shell,and the absorption peak appeared red-shifted.Adjusting the diameter of the nanocore,bule-shift of the plasmon resonance peak of nanofluids was observed as the nanocore size increased.Besides,the optical absorption performance degradation occurred when the environmental permittivity of the nanoparticles was increased. |
PDF Full Text Request