Research On The Asymmetric Composite Plane Concentrating System With The Absorber As A Flat Plate

The limited and non-uniformly distribution of conventional energy and the shortage of energy supply are becoming increasingly prominent.Renewable energy has attracted extensive attention,such as solar energy.In order to overcome solar radiation low density,the compound parabolic concentrator(CPC)is widely used because of its simple structure and high efficiency of concentrating light.Traditional CPC are mainly restricted by angle of tilt and the difficulty of fabrication technique,and that is difficult to achieve scale application.Therefore,the surface shapes of asymmetrical compound parabolic concentrator(PACPC)and asymmetrical compound plane concentrator(PACPC-P)were constructed according to the surface shape of traditional CPC.And the optical characteristics of PACPC and PACPC-P are theoretically studied by means of numerical simulation and experiment.The main tasks are summarized in the following:(1)The structure model of surface for PACPC has been established combining the principle of generalized egde ray with differential equation theory.And adopting the calculation method of radiant energy employed acquires the theory of solar direct-scattering radiation which matches with the surface structure of PACPC.The ability of PACPC to converge rays was not only influenced by the acceptance half-angle but also the surface structure.Optical efficiency of the surface structure model of PACPC is proportional to reflectivity.Radiation energy captured by PACPC distributes unevenly under rays of different incident angle.The uniformity of energy flow becomes better with the increasing of the angle of incident ray,and the position of peak focal spot of radiant energy on the absorber moves from the right end to the left end.(2)The variation of PACPC's lighting characteristics with time is acquired via the separation theory of solar direct-scattering radiation and the data of local typical meteorological year's total radiation.The improvement ratio of lighting quantity for the PACPC system shows “M” with month compared with flat system.It is obvious that the improvement ratio of lighting quantity of monthly average on either equinox is up to 24.1%.Both lighting quantity of PACPC and reflectivity have a linearrelationship(3)The surface structure of asymmetrical compound plane concentrator(PACPC-P)is obtained in term of the PACPC's surface structure combining theory of the equal acceptance half-angle,the secant method and the calculation program.Their relationship about the number of reflector and equal acceptance half-angle of the surface structure is theoretically analyzed.The results illustrate that both equal acceptance half-angle of reflector and optical efficiency of concentrator increase as the increase of the number of planes.The optical efficiency of the PACPC-P varies more quickly with the increasing number of the plane when the light incident angle is close to the equal acceptance half-angle of the surface structure,but it is less than PACPC.For the PACPC-P absorber,The distribution uniformity of surface energy tends to be better with the increase of the light incident angle,and its distribution is especially uneven at both ends of the absorber.(4)The north reflector of PACPC-P has been traced by ray to verify experimentally.It is found that the reflection of the plane surface is consistent with the theory,and its error maximum to 4%.The heat system of plane collector,PACPC and PACPC-P are established and integrating thermal characteristics are verified,the results show that both the performance of PACPC and PACPC-P are superior to that of the flat plate heat collector system in the process of collecting solar radiation within7 hours.The temperature difference of the working medium at noon reach respectively 11.5? and 6.2?,but the temperature of working medium in the PACPC-P is slightly lower than that of in the PACPC.