Research On Rolling Piston Expander And Scroll Compressor In CO₂ Transcritical Cycle

For the deterioration of ozone depletion and greenhouse effect, research on the application of natural working fluid CO2 has been became hotspot all over the world. Developing high efficiency equipments and improving the cycle performance become the key problem to promote the CO2 transcritical cycle into practice. In the dissertation, the investigation has been done with focus on CO2 rolling piston expander and scroll compressor by combining with theoretical analysis, computer simulation and experimental research.Dynamic analysis on the main moving parts of CO2 rolling piston expander is given in this dissertation. According to the mass and energy conservation principles, reasonable thermodynamics model for the rolling piston expander working process is established with suction chamber and exhaust chamber as control volume, which includes equations of friction loss, leakage loss, flow loss and expander's efficiency. With the help of EULER numerical method, the equations are solved discretely, which brings out the leakage rates through all leaking passages at different rotational angles and the rules of the thermodynamics parameters inside chambers, which can provide theoretical basis for the performance improvement and optimal design of the expander.Application of elastic mechanics theory and finite element method, finite element analysis on distortion of moving parts in the CO2 rolling piston expander under the condition of the largest pressure difference is carried out. The distortion values for the sliding vane, rolling piston and eccentric shaft under pressure difference are gained, which can provide references for the design and theoretical analysis of expander.Based on the CO2 transcritical cycle water-water heat pump system with expander and the data acquisition system, the P-V diagram test system for the expander has been set up and attained more accurate inside pressure of the expander. By adjusting the main working parameters of the system, the operating characteristic and P-V diagram of the expander are obtained and analyzed at different rotational speed. And the three kinds of probable expansion processes inside the expander are verified. At the same time, the reasonable explanation is presented that the expansion ratio at the practical operating condition is the intrinsic reason to result in the three kinds of expansion process inside of the expander. It is shown from the system performance analysis of CO2 transcritical cycle with expander that the efficiency, recovery work and coefficient of performance of the system are optimal when the expander is running near the designed rotational speed.According to related Chinese Standard and the characteristics of CO2 transcritical cycle, CO2 scroll compressor is designed and the top wrap is modified by prefect meshing profile. The tangential, radial and axial gas forces at any rotational angle of orbiting scroll are calculated and the detailed dynamic calculation and analysis for the Oldham-coupling ring, orbiting scroll and crankshaft are also presented. Considering the inreversible factors of leakage, friction, flow and heat transfer, the mathematical model for the working process of the compressor is established. The solution and analysis results for the model can instruct optimal design and provide for the future research work of CO2 scroll compressor.