| Solar energy has the advantages of clean,non-pollution,renewable and so on.It is of great significance for the sustainable development of human society to exploit and utilize solar energy reasonably and efficiently.The direct radiation density of the sun is low,people usually use solar energy in the way of gathering light first and then using it.It can be divided into four types:trough,tower,dish and linear Fresnel.Among them,linear Fresnel reflector has been favored because of its low cost,low wind resistance,simple structure and high land use efficiency.The linear Fresnel reflector?LFR?is mainly composed of a mirror field and a receiver.As the key part of the receiver,the secondary reflector?SR?plays an important role in improving the photo-thermal performance of the concentrator.Compound parabolic concentrator?CPC?is a common choice in the SR.It has excellent performance as a fixed concentrator,but it lacks flexibility when used as a SR in LFR.The high performance SR is not limited by the size of the primary reflector and can cover the whole reflector field.It has the ability to be intercepted by the vacuum tube to the maximum extent for every beam of light gathered by the primary reflector.In this paper,the optical model and physical model of linear Fresnel reflector are established based on the study of SR.On the basis of this,the optical properties of two kinds of common CPC are analyzed and optimized.An optical adaptive modeling method for constructing SR is proposed and compared with CPC.The details of the study are as follows:Firstly,based on Monte Carlo ray tracing method,the optical model of linear Fresnel reflector is established.The optical model includes primary reflector tracking inclination,solar shape and solar radiation model,photon initialization,the reflection of photons in the PR and the SR,the transmission and absorption of photons,the definition of photon statistics and the definition of optical performance evaluation parameters,and the calculation method of shadow and block length in PR field are analyzed and expounded in detail.The correctness of the optical model is verified by the comparison between the self-developed optical model and the SolTrace commercial optics software under the same conditions.Based on the self-developed optical model,the physical model of the linear Fresnel reflector is established.The physical model includes the minimum no-shadowed and no-blocked distance between the reflector fields,the focal length of the primary reflector,which includes the calculation method of width of the focused beam of the main reflector.The relationship between the maximum beam width and the incident angle is studied when the solar incidence angle starts from 45°.It is obtained that the maximum beam width decreases with the increase of the solar incidence angle when the focal length of the primary reflector varies in a large range.It is proved that it is reasonable to use the global minimum beam width to determine the focal length of the primary reflector when the transverse incident angle of the ray is 45°.The focal length of the mirror is calculated when the reflector is a cylindrical or a parabolic,and the cross-section shape of the reflector and the Local Concentration Ratio?LCR?of the vacuum tube surface are compared.The results show that there is no obvious difference in the error range of±10-5 between the two reflectors.Based on the optical model and physical model,the optical properties of CPC and optimal CPC are analyzed and compared.The distribution of light in CPC is analyzed.It is concluded that the reason why light is not intercepted by vacuum tube and CPC is missed is due to the existence of gap in CPC.The relationship between gap and convergence rate in CPC is analyzed.It is concluded that by increasing the rotation angle of the involute in CPC,a larger opening width?50mm?can be obtained with a small range reduction in aggregation convergence rate?4%?.The relationship between the convergence rate of CPC and the truncation ratio is analyzed.It is found that when the truncation ratio is 0.7,the CPC has the best convergence rate under the arbitrary rotation angle of the involute.Among them,when the rotation angle is 45°,the circular CPC reaches the optimum convergence rate of 95.8%.When the rotation angle of parabolic CPC is 50°,the optimum convergence rate is 95.4%.The relationship between the convergence rate of SR and LFR optical efficiency and truncation ratio is analyzed at different transverse incidence angles.It is found that the convergence rate of CPC is positively correlated with the transverse incidence angle.When the truncation ratio is 0.7,the convergence rate and optical efficiency reach the maximum,and at this point,the convergence rate and optical efficiency are maximum.The average efficiency of LFR with optimal CPC is 83.5%and that with parabolic CPC is 83.1%.An optical modeling method for constructing SR is proposed,and the SR is constructed based on optical model and physical model.The method takes into account both geometric and optical characteristics of linear Fresnel concentrator.The method can cover the whole reflector field and can vary flexibly according to the different configuration of the reflector field,which is not restricted by the special line shape,and can be changed flexibly according to the different configuration of the reflector field,the method can cover the whole reflector field.The ability to maximize the redirection of reflected light to the vacuum tube.The optical properties of the optical adaptive SR and the optimal CPC are compared and analyzed from different transverse incident angles,different longitudinal incident angles,tracking errors and vacuum tube sizes.The results show that the performance of the optical adaptive secondary reflector is better than that of CPC.The optical performance of LFR with an optical adaptive SR is analyzed,including the effect of the slope error of the primary reflector,the time and location factors on the optical efficiency of the LFR and the surface LCR of the vacuum tube.The distribution and variation of optical loss in LFR are analyzed in terms of transverse and longitudinal incident angles. |
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