Research On Scroll Expanders With Different Scroll Profiles

Utilizing organic Rankine cycle(ORC) to recover the engine exhaust heat is one of the effective technological approaches to realize energy conservation, emission reduction and environmental protection. Simulation research on the scroll expander in the waste heat recovery system was performed in this dissertation.Firstly, introduction of the meshing theory for scroll profiles was made, and the basic principle of scroll profiles was illustrated. Three kinds of scroll profiles were formed, including segment involute, square involute and circle involute. The effect of the involute curves on the geometrical parameters and performances of the scroll expander was analyzed.Secondly, based on the ORC system in our research group, three kinds of scroll profiles with variable wall thickness were formed on the premise of the same space and the geometric models were built respectively.Thirdly, CFD method integrated with dynamic mesh technique was employed to investigate the 3-D unsteady working process of the scroll expander. R123 was used as the working fluid, RNG k ?? model was employed to solve the Navier-Stokes equations. PISO algorithm was employed to solve the pressure and velocity coupling problem. The pressure, velocity and temperature distribution in the scroll expander with different crank angles were obtained and the discharge process was analyzed.Finally, as the working process of the scroll expander is unsteady, the parameters like mass flow rate, output torque and output power change over time. The working processes of three variable wall thickness scroll expanders were simulated and the influence of the scroll profile type and working conditions on the performance of the scroll expander was analyzed. Simulation results indicated that for the scroll expander used in our research group, the involute of circle with variable radii had better performances compared with the conventional scroll profile. When occupied the same space, the involute of circle with variable radii wraps had an increase of the output torque, output power and efficiency, while the hybrid wraps presented a reduction of performances. Under the premise of the same inlet and outlet conditions, the output torque decreased with the rotation speed, the output power and the efficiency first increased with the rotation speed and then decreased. When the rotation speed and the inlet superheat were fixed, the output torque and output power increased with the inlet pressure, and the efficiency had a slow growth.