Preliminary Design And Numerical Investigation On Off-design Performance Of A Radial Inflow Turbine Using Organic Working Fluids

As a kind of speed expander,radial inflow turbines are widely used in organic Rankine cycle power generation systems for has the advantages of compact structure,small flow rate and high efficiency.Its operating characteristics have a crucial impact on system performance.The research on radial inflow turbine is of great significance for improving the performance of organic Rankine cycle system.This paper compiled a one-dimensional design calculation program for radial inflow turbines,and constructed the simulation model for the turbine,against the background of geothermal energy utilization.The performance of the turbine with R245 fa and R245fa/R134 a under design and off-design conditions was numerically simulated by computational flow dynamics method,which provides a theoretical reference for the performance prediction and off-design operation of radial inflow turbines.The main work content and related conclusions of the thesis are as follows:1)One-dimensional design and three-dimensional modeling of radial inflow turbine.Taking the inlet temperature,inlet and outlet pressure and working fluid mass flow as the initial design parameters,the power output and isentropic efficiency of the turbine as performance indicators,and combining the flow loss model,the one-dimensional design calculation program for radial inflow turbine aerodynamic structure is compiled by using MATLAB software.Determining the geometric parameters of the main components such as volute,nozzle and rotor.Then the geometric model and simulation model of radial inflow turbine are constructed according to the design results.2)The off-design performance of the radial inflow turbine with pure working fluid.The aerodynamic characteristic of the turbine are simulated and analyzed when R245 fa is selected as working fluid.The effects of inlet temperature,inlet and outlet pressure,impeller speed and expansion ratio on turbine performance are studied.The results show that the flow state of working fluid is good,and the power output and isentropic efficiency are 224.32 k W and 84.56% respectively.The orthogonal simulation experiment and range analysis show that among the main operating parameters,the inlet pressure has the greatest influence on the power output of the turbine and the inlet pressure has the greatest influence on the turbine power output,while the temperature has the least effect.For isentropic efficiency,the influence of impeller rotational speeds is the greatest and outlet pressure is the smallest.3)Simulation and analysis the effect of mixture ratio on the performance of the radial inflow turbine.The results show that under design conditions,when the mass fraction ratio of R245 fa to R134 a is 7:3,the isentropic efficiency of the turbine is the highest.Turbine power output and isentropic efficiency are 9.37% and 2.47% higher than pure working fluid R245 fa,respectively.4)The off-design performance of the radial inflow turbine with optimal mixing ratio.Within the simulated temperature range,turbine isentropic efficiency only varies by 1.70% at the design rotational speed,which is more adaptable to the change of inlet temperature than pure working fluid.The optimum operating speed of the turbine is 95-115% of the design value,and the isentropic efficiency of turbine average decreases by 11.33% at lower rotational speed.The optimum expansion ratio of centripetal turbine is 3.33 at design rotational speed,and the optimum expansion ratio increases with the increase of rotational speed.When the expansion ratio is higher than the optimal value,the change of inlet temperature has no significant effect on the turbine isentropic efficiency.