Carbon Dioxide Transcritical Cycle Characteristics And System Control

Study at home and abroad have shown that, due to the advantages of its properties in latent heat of vaporization, specific heat, kinematic viscosity and so on, adopting appropriate refrigeration cycle, the carbon dioxide will have a more superior performance compared to the traditional refrigerant in the thermal characteristics.From analysing the thermodynamic properties of trans-critical carbon dioxide cycle, simulating the basic theory cycle, this article studys how the operating parameters impact the coefficient of performance of the cycle. Based the analysising of the characteristics of the cycle, this paper discussed the impacting to COP of every method which can improve the coefficient of performance of the basic theory cycle cycle, such as middle regenerator, expansion valve, two-stage compression, bypassing valve.In this paper, the optimal high-pressures of cycles with expander and two-stage compression have been analysed. The related software has been used to simulate these two cycles in orde to analyse the impacting to the optimal high-pressures of every system operating parameters. According to the simulation data, this paper fited the calculated correlation of hese two cycles. As a result of the actual run-time system, it is difficult to control the high pressure to the point with optimal high-pressures at any time, so in this paper, control precision of the optimal high-pressures of the cycle has been analysed at different operating conditions and different needs for the coefficient of performance of the cycle.By analyzing the existing control methods of the system of carbon dioxide, using reference of control measures of traditional refrigerant system, this paper has proposed a coupled control method for trans-critical carbon dioxide refrigeration system. This control system takes the demand of the optimal high-pressures and cooling capacity of the cycle into account at the same time. It takes the compressor control and electronic expansion valve control associated by adoption data fitting. According to different ambient temperature it adjusts the objective of system control. This control system could realize the synchronization and stability of the system control.It needs to establish the system dynamic simulation model for checkouting the performance of control program and tuning parameters of the control algorithm. In this paper, based a detailed analysis of the dynamic response characteristics of every component to carbon dioxide trans-critical system and a reference of the existing modeling methods of cooling system components, a suitable model has been established for every component of carbon dioxide trans-critical system which will be used for the study on control. Detailed analysis of the inter-relationship between input and output parameters of every component has been down and a calculation process of system dynamic model has been established. Finally, model was verified.The results of this paper will provide a reliable reference for the performance improvement, control strategy research and control program inspection of carbon dioxide trans-critical cycle.