Optical-Thermal Design And Analysis On Compact Space High-Temperature Solar Reciever

High-temperature solar receivers are key equipment for converting concentrated solar energy into high-temperature thermal energy.It has wide application demand in the field of ground solar power generation,thermochemistry and other high-temperature solar energy utilization technologies.In the technical fields of space solar thermal applications,it is required that the solar receiver is lightweight,compact,efficient,reliable and has high energy storage density.And,the thermal conversion temperature exceeds 1200 K,which brings many challenges to solar high-temperature thermal conversion technology.In addition to materials and process technology,insufficient research on the mechanism and characteristic of solar high-temperature thermal conversion technology based on optical windows and high-porosity foam materials,and lack of experimental data are the key issues that restrict the fine design and material selection of such high-temperature solar receiver.According to the development needs of high-temperature thermal conversion technology of space solar energy,this paper aims at the characteristics of solar and thermal radiation transport as well as energy conversion of the overall structure of solar receivers and key components such as spectrally selective solar windows,high-porosity foam absorber,high-temperature solid-liquid phase change thermal storage units,etc.The energy conversion characteristics are studied,and the principle prototype is developed and tested.Firstly,a transient thermal field infrared thermal image measurement method is proposed to measure the energy flux distribution of the concentrated spot in order to meet the test requirements of the incident characteristics of concentrated sunlight in the experimental research of high-temperature solar thermal conversion.Based on the infrared thermal image data of the transient change of the target surface,combined with the particle swarm optimization algorithm of the three-dimensional heat transfer inverse problem,the energy flux distribution of the incident sunlight was identified and obtained.Furthermore,a test method for identifying the distribution characteristics of the focused beam direction is proposed by combining the infrared thermal image data of the moving target with the Backward Monte Carlo simulation.The test method was verified by taking the xenon lamp simulator in our laboratory as the object.Aiming at the characteristics of the optical window being heated by the hightemperature absorber and the pressure of the heat transfer fluid at the same time,a window structure design idea of separation of thermal and mechanical loads is proposed,and an intermediate gas-cooled double-layer window structure scheme is constructed.The coupled multi-spectral radiation heat transfer model and MC-FVM calculation method of the optical window are established,and the optical-thermal coupling transport analysis calculation program of the window structure is developed.Considering the temperature distribution in the receiver cavity and the spectral selectivity of the quartz window,the effect of the structural parameters of the intermediate gas-cooled double-layer window on its operating temperature and solar-to-thermal conversion performance under the irradiation of the parabolic dish concentrator was analyzed.Furthermore,the transmission process of the concentrated lights by the optical windows with different surface shapes is studied.The transmission characteristics and energy loss mechanism of three typical quadric surfaces,ellipsoid,paraboloid and hyperboloid,and non-uniform rational B-spline free-surface optical windows to concentrated sunlight are analyzed.With the goal of maximizing the optical efficiency,based on the optical path analysis and genetic algorithm,the curved surface shape and contour parameters of the solar optical window were optimized.For the thermal conversion structure composed of the optical window and the high-porosity foam absorbor,the incident direction and spectral distribution of the external concentrated sunlight,the spectrally selective radiation-conduction heat transfer effect of the window,the solar and thermal radiation transfer in the absorbor,the thermal conduction of the foam skeleton and the local thermal non-equilibrium convective heat transfer with the fluid flow,the MC method combined with the finite volume method is used to establish an analytical model of the coupling process of energy transfer and conversion in this type of high-temperature solar thermal conversion structure.The high-temperature heat transfer characteristics of the structure subject to concentrating light of the dish were studied,and the effects of the energy loss path,the parameters of the heat transfer structure and the fluid flow parameters were analyzed.Furthermore,an improved high-temperature heat transfer structure composed of annular double-layer quartz window/foam absorber in the intermediate gas-cooled inner layer is proposed,and its high-temperature heat transfer characteristics and influencing factors are numerically simulated.On this basis,the principle prototype of the window/columnar foam absorber/outer flow channel combined high-temperature solar receiver was developed,and based on the xenon lamp solar simulator,respectively for the single-layer window and the intermediate gas-cooled inner layer annular double-layer window.The two heat transfer structures were experimentally tested for conversion performance.It is proved that the high-temperature solar receiver using the intermediate gas-cooled inner layer annular double-layer window has higher solar-to-thermal conversion efficiency and lower pressure-bearing window temperature.Aiming at the technical requirements of space solar dynamic power,a thermal storage high-temperature solar receiver structure scheme is proposed,which is composed of an optical window and an integrated unit tube for solar absorption/phase change thermal storage/foam enhanced heat transfer.The MC method is used to simulate the solar and thermal radiation transport,and the enthalpy method is used to solve the solid-liquid phase transition process,and the periodicity of incident sunlight transport and absorption,high-temperature conduction and phase transition of the thermal storage layer,and high-temperature coupled heat transfer between the foam and the He-Xe is realized.The dynamic high temperature heat transfer characteristics and influencing factors of the integrated thermal storage/enhanced heat exchange tubular unit using Na F phase change material,nickel foam and He-Xe gas flow were analyzed by numerical simulation.On this basis,combined with the periodic sunshine conditions of the space flight orbit,the design of the thermal storage high-temperature solar receiver was carried out,and the orbital periodic energy conversion,storage and transmission characteristics of the solar receiver under the incident light of the dish concentrator were investigated.Numerical simulation analysis was carried out.The above research has provided a numerical simulation method for the coupled solar and thermal radiative transfer and energy conversion process in the solar receiver for the development of lightweight,high-efficiency,and compact space high-temperature solar receiver technology with a thermal conversion temperature above 1200 K,solved the problem of measuring the focused light characteristics of the xenon lamp solar simulator,and revealed the control mechanism of the high-temperature solar-to-thermal conversion efficiency,the characteristics of energy conversion,light and heat transfer and the effect of design parameters of several typical high-temperature thermal converter structures are obtained.It provides theoretical basis and key technical support for the development and application of space solar high-temperature thermal conversion technology.