| Organic Rankine Cycle(ORC) power generation technology plays an increasing prominent advantages in the recovery and utilization of low grade heat energy. A turboexpander which has excellent performances is the foundation to ensure the safety and efficiency of the whole cycle system operation. A radial-inflow turbine is set as the system turboexpander, and design method for a radial-inflow Organic turbine is studied, internal flow characteristics is analyzed and off-design features are investigated. These researches play academic significances to the development of ORC technology.In the first part, equations of state to calculate the properties of organic working fluid are discussed. Setting R245 fa as working fluid and SW equation as standard reference equation, deviations of specific volume, sound speed, internal energy, enthalpy and entropy calculated by state equation of ideal gas and PR equation are compared with the results calculated by SW equation. Utilizing the CFD software ——FLUENT, method of adding organic working fluids to the material database is investigated, and numerical simulation is conducted on an ORC 2-D nozzle, influences of compressibility factor, density, sound speed, absolute speed and March number distributions along the blade surface and aerodynamic parameters of mass flow rate and nozzle outlet angle with different equations are analyzed. Results show that: no matter in the terms of calculating thermodynamic parameters or simulating the aerodynamic parameters, deviations of the results calculated by ideal-gas equation are far away from that calculated by PR equation, so organic working fluid can’t be set as an ideal gas. On the other hand, there is a small deviation between the calculated results of PR equation and SW equation, besides, high accuracy, simple structure and widely application scope of PR equation make it as the equation of calculating thermodynamic parameters in the terms of organic working fluid turbine design and inflow characteristics research.On the basis of the study of working fluids properties, setting the optimized parameters of a 120 kW Organic Rankine Cycle as designed goal, an organic radial-inflow turbine is designed and its inflow characteristics are analyzed. Geometry sizes of the turbine nozzle and blade flow passages are determined by 1-D thermodynamic calculation. TC-4P airfoil and island airfoil are 3-D modeled to be the nozzle airfoil, and turbine blades are 3-D modeled by ANSYS Bladegen. Numerical simulation of the whole turbine is conducted by ANSYS CFX, the consistency between the results of 1-D thermodynamic design and 3-D numerical simulation verifies the accuracy of turbine design method. The simulation results show that, compared with island airfoil, the degree of pressure drop along the nozzle surface is gentler, the range of total pressure loss is smaller and efficiencies at off-design conditions are higher. When the number of rotor blades is set as 15, efficiency of the turbine is highest and flow separation area is relatively small, so TC-4P airfoil and 15 are respectively set as the nozzle airfoil and optimized rotor blade number of this 120 kW ORC radial-inflow.A method to calculate the radial-inflow turbine performance parameters is proposed, and the parameters are computed by MATLAB programing, and the consistency with CFD 3-D numerical results verify the affectivity and reliability of this calculation method. Setting the optimal efficiency as goal, the optimal regulation modes when inlet pressure, mass flow rate and outlet pressure varies are investigated. Results show that, when inlet pressure varies, turbine efficiency will be higher with speed regulation method. The adjustment range is broader and turbine efficiency is higher with nozzle angle regulation method when mass flow rate varies. When outlet pressure varies, nozzle outlet area adaptive regulation method can keep a relatively high turbine efficiency, speed regulation method will demonstrate its superiority only when outlet pressure exceeds a certain value. |
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