| For the past few years,the direct absorption solar collector(DASC)is a cost-efficient approach to absorb the solar energy,which has received extensive attention from many researchers.Many factors would affect the performance of DASCs,including solar radiation,volume fraction,mass flow rate and optical thickness.Among them,the optical properties of nanofluids has decisive effect on the performance of DASCs.We thought up a creative idea for using nonspherical nanoparticles with the influence of mass flow rate.In this paper,a research model for the study of the nanorods particle size,shape,and the angle of the light incidence,the concentration of the nanofluid,and also considering the infl uence with a variety of flow rate is constructed as the nanofluids optical properties model.The experimental research on nanofluids practical optical characteristics is adopt to study optical properties of nanofluidsAccording to the radiation intensity of each band of solar spectrum,nine kinds of commonly used nanoparticles were selected to analyze the effect of optical constants on extinction.The results show that gold nanoparticles are suitable for the performance analysis of direct absorption solar collector based on nanorod fluid.There are two plasmon resonance peaks of gold nanoparticles,the longitudinal plasmon resonance peak is located at 1020nm,and the extinction factor is 20.1.A2D-Monte Carlo method coupling with discrete-dipole approximation(DDA)was proposed to investigate the effect of length-radius ratio,effective radius and incident light angle of Au nanorods(Au NRs)on the optical characteristics and analyse solar weighted absorption coefficient of DASCs.Results indicated that flow characteristics and morphological changes are suggested to signally improve the absorption characteristics of Au nanorod-fluids.The transmittance of Au/water nanorod-fluids(WB-Au NRFs)under specific flow guidance was 19.8%less than that with a disordered state at full spectrum.With appropriate flow regulation,the solarweighted absorption coefficient can reach 61.1%,while that of disordered state was only 52.1%.Meanwhile,a linear relationship between transmittance and the length-radius ratio,as well as the effective radius,was observed by theoretical study.Based on the simulation results,the factors affecting the photothermal characteristics of Au/water nanorod-fluids were further analyzed.The effects of light intensity,flow rate and concentration on the photothermal characteristics of nanorod fluid were analyzed.The higher the intensity of light,the higher the final temperature of the Au/water nanorod-fluids can reach,and the more rapidly the temperature change.The outlet temperature of the nanofluid increased with the increase of illumination intensity,especially for the 0.5mL/min flow rate control,600W/m~2irradiation,the outlet temperature of the nanofluid increased by 18.5%.The photothermal properties of nanofluids are closely related to the variation of the temperature of nanofluids with the time of solar radiation.The optical properties of nanofluids depend largely on their concentration.The addition of gold nanorods significantly improves the heat absorption performance of deionize d water.The temperature of the nanofluid rises faster than that of the deionized water during the irradiation time.When the flow rate of 0.3ppm gold nanorods is controlled at 0.75mL/min,the photothermal conversion efficiency can reach 52.3%,which is 16 2%higher than that without flow rate control.It is of great significance to add nanorod particles into direct absorption solar collector and control them by flow rate. |
