Modelling, numerical and thermodynamic analysis of radial turbine used in micro organic rankine cycle

This thesis investigated Organic Rankine Cycle (ORC) systems used for on-site power generation. The study focused on the design and analysis of radyal turbines used in ORC systems. Factors such as rotor inlet angle, rotational speed, working fluid and inlet temperature were investigated to understand their effects on turbine efficiency. It was found that increasing the rotor inlet angle resulted in an increase in rotor inlet speeds. However, beyond an angle of approximately 78 degrees, a decrease in turbine inlet velocities was observed. Furthermore, while increasing the turbine speed almost tripled the speed, the rotor inlet angle changed by only 3%. Surprisingly, this change in speed resulted in a significant 12% increase in turbine efficiency. It was also found that at low speeds larger rotor inlet and outlet radii were required, while increasing speed resulted in a reduction in rotor dimensions. Increasing the speed from 40 000 to 120 000 rpm resulted in an average reduction in rotor radii of approximately 66.7%. In addition, increasing the turbine inlet temperature from 90 °C to 180 °C resulted in an approximate 18.1% increase in the turbine inlet radius. The effect of turbine speed on power generation was found to be less significant compared to changes in expansion ratio. For example, increasing the speed from 40 000 to 120 000 rpm at an expansion ratio of 8 resulted in an approximate 2% increase in thermal efficiency. However, at 80 000 rpm, increasing the expansion ratio from 2 to 11 resulted in a remarkable 141% increase in thermal efficiency. In the ORC system, the performance varied depending on the working fluid used (R245fa, R123, R365mfc, R1234yf, R1233zd(E) and R1234ze(E)). The highest power output was obtained with R1233zd(E), while the lowest power output was obtained with R123. Three-dimensional numerical analyses were performed to investigate the turbine flow velocity, pressure changes and turbulence. Turbulence and pressure changes were identified as significant factors affecting turbine efficiency.