Photo-thermal Characteristics Analysis For Concentrating Radiation Thermal Decomposition Process Based On Ferrite

Solar energy utilization is one of the most promising routes to solve fossil fuel shortage, environmental pollution and greenhouse effect in 21 s t century because of its abundance and environment friendly. Solar thermochemical technique is used concentrated solar radiation as high temperature heat source to drive chemical reaction. During the process, the solar energy is converted into fuels with the assistance of thermochemical reaction, which is largely employed in hydrogen production and greenhouse gas emission reduction fields. The energy conversion process, which combines solar energy and thermochemical reaction, not only improves the energy grade, but also stores the solar energy as secondary fuel. Solar thermochemical technique can solve the unstable and un-continuous problem in solar energy utilization field and effectively improve the overall system efficiency. Among the redox materials used in solar thermochemical hydrogen production, MFe₂O₄（M=Ni, Co, Cu, Zn, etc） redox pair is a promising candidate for solar thermo-chemical hydrogen production since its relatively low dissociation temperature, good redox performance and high hydrogen yield.Based on the background of solar thermo-chemical hydrogen production utilization as well as the requirement of applied technology development of high effective and low cost solar energy utilization, this dissertation will research on the photo-heat characteristic during the solar thermal dissociation process of Ni Fe₂O₄ with the assistance of numerical and experimental methods. The main researches of this dissertation include the following aspects:Chemical co-precipitation method is employed to synthesize ferrite particle(Ni Fe₂O₄, Cu Fe₂O₄, Mn_0.9Cu_0.1Fe₂O₄) that is suitable for mediumhigh temperature solar hydrogen production. XRD, SEM, FTIR, etc. are employed to analyze their purity, particle geometry and porosity, etc. The mass loss curve and dissociation temperature of Ni Fe₂O₄ and Cu Fe₂O₄ particles are obtained with the help of thermogravimetric analyzer at different heating rate. Flynn-Wall-Ozawa method is employed to calculate the thermal dissociation kinetics parameters（activation energy, preexponential factor, and kinetic mechanism） of Ni Fe₂O₄ and Cu Fe₂O₄ based on the mass loss curve.In order to obtain the radiative properties of materials, a spectral transmittance-reflection measuring system is built and the measuring relative error and measuring uncertainty are also analyzed with the experimental results of a standard sample that measured by China Institute of Metrology. Spectral transmittance of ferrite particles is experimentally measured through KBr pellet method in wavelength range 0.5-2.1 μm. Mie theory and K-K equation are employed to calculate the complex refractive index with inverse problem model based on the experimental results. Besides, the relationship between absorption coefficient of ferrite particle and temperature are also investigated by Planck mean absorption factor method.A multi-layer and multi-dishes concentrating model is developed based on a solar concentrating system, and the revised designing parameters and the flux distribution on the focal plane are also acquired. Energy dispersing phenomena at the focal plane of the system which is caused by the supporting bolt moving of each small concentrator is also investigated with the help of numerical simulation and theoretical analysis method. A solar reactor heat transfer model is developed by adopting Monte Carlo and Finite Element combined method based on the complex physical field during the thermal dissociation process of Ni Fe₂O₄. Effects of particle diameter, mass flow rate, velocity and temperature of protection gas on temperature, fluid field and reaction conversion rate are numerically investigated based on the model. The heat transfer performance of a cavity solar reactor is experimentally studied based on a solar thermochemical experimental system, and the effect of direct normal irradiation and mass flow rate of protection gas on temperature field inside reactor is also obtained.Exergy theory and UDF technique are employed to numerically investigate the exergy（physical exergy and chemical exergy） distribution inside the solar reactor based on the results of solar reactor model at different operating parameters（particle diameter, mass flow rate, velocity and temperature of protection gas）. Besides, second law of thermodynamic is employed to acquire the overall cycle efficiency and solar-to-fuel efficiency based on an ideal Ni Fe₂O₄ and Cu Fe₂O₄ redox pair solar thermochemical recycled process. The above results are helpful for optimizing the geometry of solar reactor and the experimental operating parameters.