Abstract: Few studies have focused on the overall performance and internal flow field of small-scale turbine under off-design conditions in an organic Rankine cycle (ORC) system. The small-scale turbine of an ORC system is often used at variable rotation rates for renewable energy and waste heat utilization. The 3D flow field of a small-scale, radial-axial flow turbine impeller is simulated with CFX software and verified by experimental data and design data, which uses R123 as work fluid. The variations of thermal efficiency and isentropic efficiency of impeller with the rotating rate are provided. The leaving-velocity loss of the turbine is the main cause of 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, is also proposed. The flow direction of working fluid should be considered when calculating the leaving-velocity loss at the outlet of the turbine. The isentropic efficiency of the turbine is evidently low at less than 20000 r·min^-1, whereas the kinetic energy difference between the inlet and outlet of the turbine impeller is close to 0 at 60000 r·min^-1.

Key words: organic Rankine cycle, turbine, R123, flow, numerical simulation, renewable energy

摘要： 目前针对有机朗肯循环(ORC)系统小型涡轮在变工况下运行性能的研究很少,对运行性能随涡轮转速的变化机制缺乏了解.而在可再生能源及余热利用过程中,ORC系统小型涡轮常处于变转速工况.把实验数据和设计数据相结合,针对采用R123为工质的小型径-轴流式高转速涡轮,采用CFX软件对涡轮叶轮三维流场进行了数值模拟.给出了热效率和叶轮等熵效率随转速的变化趋势,指出余速损失是低转速下热效率降低的主要原因.提出了修正后的涡轮能量公式,在低转速工况下对涡轮的做功性能分析时不能忽略涡轮进出口的动能变化,在计算涡轮出口的余速损失时,必须考虑工质流动速度的方向特性.

关键词: 有机朗肯循环, 涡轮, R123, 流动, 数值模拟, 再生能源