| Energy is the lifeblood of the national economy. Energy and human survival environment and people’s lives have close relations.Energy plays a pivotal role in the economic and social sustainable development. In order to achieve the goal of low-carbon energy and low-carbon economy, we must vigorously develop renewable energy, develop and utilize new energy, the utilization of solar energy is a very important aspect. Solar thermal power generation technology due to achieve large-scale solar energy use, got rapid development in recent years. Organic Rankine cycle is one of the most promising use of technology in middle-fow temperature thermoelectric conversion field. Compared with the steam Rankine circulation, in the utilization of middle-low temperature heat source, organic Rankine cycle can make the expander get higher efficiency, and shows the advantages of better thermodynamic performance. Organic Rankine cycle technology has been successfully used in the industrial waste heat recycling, combustion of biomass energy, geothermal energy, solar thermal power generation, etc. The technology on higher than100kW power has reached a maturity worth considering. Solar heat collection technology can achieve the development of middle-low temperature heat source. Combined with organic Rankine cycle, solar organic Rankine cycle thermal power generation technology is a kind of new energy utilization technologies. Solar organic Rankine cycle has great potential to meet thermoelectric demand of residents from10kW level to100kW. It has a big advantage in high concentrated solar power, is easier to implement energy collection and storage.As a core component of the ORC system, expander has a vital role in the overall system performance. To date, two main types of expanders are applied in ORC which can be classified into two types:First one is the velocity type, such as axial turbines and radial-flow turbines; the other is positive displacement type, such as scroll expanders, screw expanders, piston expanders and rotary vane expanders. The author has carried on the experiment and numerical simulation research on a small-scale radial-axial flow turbine used in organic Rankine circulation mainly in the following three aspects of research:(1) Few existing studies have focused on the overall performance and internal flow field of small-scale turbine under off-design conditions in an organic Rankine cycle system (ORC). The small-scale turbine of an ORC system is often used in the variable rotation rate operating condition of renewable energy and waste heat utilization. The3D flow field of a small-scale, radial-axial flow turbine impeller was simulated with CFX software and verified by experimental data and design data, which uses R123as work fluid. The variations of the thermal efficiency and the impeller’s isentropic efficiency with the rotating rate change were provided. The leaving-velocity loss of the turbine is the main cause of the lower thermal efficiency at a low rotation rate. A revised equation for calculating the power output of a small-scale turbine under the off-design condition, which considers the change in the kinetic energy between the inlet and outlet of the turbine, was also proposed. The flow direction of the working fluid should also be considered when calculating the leaving-velocity loss at the outlet of the turbine. The isentropic efficiency of the turbine was evidently low at less than20000rpm, whereas the kinetic energy difference between the inlet and outlet of the turbine’s impeller was close to0at60000rpm.(2) Currently the research on performance of small-scale turbine used in organic Rankine circulatory system drived by different organic working medium is rare, the understanding about performance of different organic substance in the same small radial-axial high speed single stage turbine is lacking.In the process of renewable energy and waste heat utilization, we need to choose a suitable working medium for small turbine used in organic Rankine circulation system according to the heat source temperature. At first, the author combined the experiment data and design data, then finished three dimensional flow field numerical simulation in turbine impeller by CFX software, the result showed that this method can predict the performance of the turbine.Then compared the performance of the turbine drived by R11,R123and R141b under different heat source temperature.(3) Thermal efficiency of Organic Rankine Cycle system depends largely on the performance of the turbine, the engine shaft power is not only determined by the inlet temperature, inlet pressure, rotation speed, enthalpy drop, etc in the turbine process but also the nozzle angle of attack.Theoretical and experimental support in studying small-scale turbine performance in different angle of attack especially driven by different organic working medium is rare. This paper first selected three kinds of organic working medium that is suitable for solar ORC system, then presented a quantitative study on the working performance of a small-scale radial-axial turbine used in ORC system in attack angle from35to75degrees when it is drived by organic working medium Rll,R123,R141b respectively. A fluid dynamics model is built and validated. The simulation results show that when the turbine running at60,000rpm, the best attack angle of R11was-78degrees,maximum thermal efficiency of system was11.31%, The best attack angle of R123was-70degrees, maximum thermal efficiency of system was10.93%, The best attack angle of R141b may be less than-79degrees according to the trend, established maximum thermal efficiency of system was9.14%. The main factors influencing the system thermal efficiency are ΔH and ΔEk. |
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