Design of a miniature low-grade heat-driven ORC system and performance evaluation of its partial admission radial turbine

The low-grade heat from petrochemical industry, automobile exhaust, geothermal resource and other fields is so vast that it's a good direction to endeavor to utilize it considering the environmental and economic value. Compared to the Rankine Cycle with water as its working substance, it is effective to utilize Organic Rankine Cycle (ORC) to utilize low-temperature heat. We plan to develop commercial products with ORC system to use low-temperature heat under 350°, certainly, experimental verifications should be carried out firstly. In this paper, an experimental miniature ORC system with R11 as its working substance was proposed firstly and the thermodynamic analysis was conducted. The results of thermodynamic parameters showed that this system could utilize the low-temperature heat and obtained efficient power output. Later, the turbine of the system was designed as a partial admission (Σ=0.267) high rotational speed (n=60000 rpm) radial turbine based on the system thermodynamic parameters, and the aerodynamic analysis of the radial turbine was fulfilled to ensure its safety and efficiency. Finally, we constructed a test bench based on the above analysis to validate the proposed ORC system and designed turbine. At the operating condition, the simulated parameters, such as axial force of rotor, power generated and thermal efficiency of the radial turbine, were analyzed. In addition, the unsteady aerodynamic blade forces and frequencies of unsteady disturbances and excitation force factors were obtained by spectrum analysis. The detailed flow structures in the channel were observed and analyzed corresponding to the performance parameters variations. The results revealed that the partial admission greatly influenced the parameters distributions and the energy losses of radial turbine mainly occurred in the vicinity of the hub frontier. All the performance and design optimization show the proposed system is capable for experimental study and could produce more exhaustive experimental results.