Experiments And Simulations On Performance Of High-temperature Solar Particle Receiver

Solar energy has attracted an increasingly attention as a clean renewable energy due to the growing demand of energy and pressure of environment. Concentrating Solar Power (CSP) can provide a stable and high quality electrical output because of the heat storage ability. Therefore, it is considered to be the most promising to replace the basic electrical load in the futher. The CSP Dish system has the highest concentration ratio and efficiency. However, the systematic stabilty and lifetime are seriously affected by the hotspots and non-heat-storage unit in the normal CSP Dish system. Developing an immuning to the hotspots and carrying the heat storage receiver for CSP dish system is the key to solve these problems.In this thesis, the prospects, applications and developments of solar energy at home and abroad are firstly introduced. The particle heat-collecting method is very helpful to avoid the damage from hotspots and the tight sealing in the HTHP. Besides, this method is able to store heat directly, which will be a good choice for solar high temperature heat-collecting. The lifetime and efficiency of CSP system mainly depond on the receiver, which is the most critical component to convert the solar energy to thermal energy. Two types of particle receiver system were built and the solar simulator system was built, the radiation flux measurement method was studied, the particle physical performance was measured, and the experimental method of particle heat-collecting was presented, which lay a foundation for the next discussions.Based on the Monte-Carlo ray tracing method, two receiver optical models were built by coupling the parallel rays source model and the receiver without cone cover, and coupling the high concentrating rays source model and the receiver with cone cover. The optical simulation results indicated the optical efficiencies were-84% and-87%, the maximum irradiance reached 44.7 kW/m2 and 232.3 kW/m2 for the receiver without and with cone cover, respectively. The optical model results were the inputs of the thermal models. Two coupled optical and thermal models, including the steady one for the receiver without cone cover and dynamic one for the receiver with cone cover, were built by analyzing the convection, conduction and radiation heat transfer in the receiver, which were demonstrated by the experimental results.For the receiver without cone cover, it fits the concentrator system with a big focus spot radius. The particle temperature increase in a single pass increased from 200℃ to 300℃ and the thermal efficiency dropped from 63% to 59% when the radiation power on the aperture rose up from 1050 W to 1550 W. The model forcasted the temperature increase would continuously go up to 1150℃ and the thermal efficiency decreased to ～34% when the radiation power increased to 13000 W. The heat loss analysis indicated the radiation heat transfer between the receiver inner wall and glass cover, and the heat losses from glass cover reduced the receiver efficiency.The way to enhance the receiver efficiency is reducing the radiative angle factor from receiver inner wall to glass cover, coating a FIR reflective film on the back of glass cover, or coating a selective absorbing film on the particle surface.For the receiver with cone cover, it fits a concentrator system with a small focus spot radius. The particles at the outlet were heated to ～650℃ and the thermal efficiency was 60.5% when the radiation power was 5079 W. The heat loss analysis indicated that the way to enhance the receiver efficiency was increasing the insulation materials between the steel surface and the electromagnet, which would make the receiver efficiency go up to more than 70%. When the receiver with cone cover and thicker insulation was combined with a 3 m two-stage dish concentrator, the simulation results showed the optical efficiency and thermal efficiency would reach 84.8% and 76.9%, respectively, and the particle temperature at the outlet would reach 673℃. And then, a 3 m dish heat collection and storage particle system was designed.The temperature distribution investigation is important to enhance the receiver efficiency and avoid the hotspots. A novel TLBE radaiton boundary condition treatment was proposed to overcome the heat flux jump on the interface. A 3D TLBE-MC optical and thermal model was built by coupling the TLBE method and Monte-Carlo method, which was demonstrated by the experimental results. The model indicated the particle would rise up 1400℃ fastly when the particles flew into the receiver and then decreased gradually to 700℃ because the heat transfer between the particles and the cone cover.In conclusion, the aim of this thesis is to develope the solar dish high-temperature heat-collecting with heat storage system. A stable particle mass flow and long residence time high-temperature particle heat-collecting was proposed. The particle outlet temperature reached 650℃ and the receiver thermal efficiecny was kept above 60%. A more than 70% thermal efficiency was obtained if the receiver was improved. Based on the optical and thermal coupled model, the optical losses and the heat losses were analyzed, and the methods to improve the reciever performance were discussed. A 1st-order calculation accuracy boundary conditon treatment for the radiation boudary in the TLBE was proposed. A 3D TLBE-MC model was built by coupling the TLBE method and the Mento Carlo method. The temprature distribution, heat transfer process and air velocity distribution in the receiver were investigated, which provided a base for the high-temperature heat utilization.