Preliminary Study On The Computer-aided Construction Of Thermodynamic Cycle

To achieve the goal of carbon peak and carbon neutral,it is necessary to increase the proportion of renewable energy consumption.As the core of energy conversion system,thermodynamic cycles have been studied for a long time.Due to the volatile and decentralized natures of renewable energy,multi-energy complementary technology is often required.This increases the complexity of energy systems,which requires the integration of multiple forms of thermodynamic cycles.As a representative of supercritical cycle,the supercritical CO₂（S-CO₂）Brayton cycle has great application potential combined with high-temperature thermal energy.Subcritical cycles have good applicability to low and medium temperature energy sources.However,the research on the cooperative optimization of the structures and parameters of the two types of cycles is still insufficient.The free-superstructure method is used to design the S-CO₂ Brayton cycle and the cooperative optimization of parameters and structure can be realized.To simplify the cycle,the heat transfer part of the Brayton cycle is separated.The cycle is converted into a coded form that the computer can recognize,and the complex cycle is built by the combination of elementary cycles.A two-layer algorithm based on genetic algorithm is designed and the accuracy of the algorithm is verified.Then three cases are studied and the specific works increase by 47.97k J/kg,46.50k J/kg and 42.59k J/kg,respectively.Based on two elementary cycles,all constructible cycle structures are compared and the best basic configuration is found to be the Brayton cycle with reheating and inter-cooling.Finally,the heat transfer network is designed based on pinch point technology,and the complete thermodynamic system is obtained.Based on the generic-structure method,the forms of subcritical cycles are explored.To optimize the cycle more comprehensively,the databases of structure and working fluid are established.By analyzing the characteristics of the subcritical region,the corresponding construction rules are formulated.The thermodynamic cycles of the four-process,five-process and six-process are constructed by the combination of thermodynamic processes,and 10 feasible structures are screened out storage in the structure database.30 different working fluids are selected and the relevant physical parameters are called through REFPROP 9.1.The working fluid database is formed by these working fluids and parameters.By genetic algorithm,the cooperative optimization of subcritical cycle structure,working fluid and parameter is realized,and the influence of temperature on cycle efficiency is analyzed.Compared with the traditional Rankine cycle,the efficiency of the new cycle can be improved by 9.96%,which shows that this method has a good ability of cycle construction and optimization.Through the design of supercritical cycle and subcritical cycle,it is shown that the computer-aided construction method can play an important role in the design of the thermodynamic cycle.It can reduce the dependence on designer’s experience,shorten the design period and realize the collaborative optimization of cycles,which is of great significance to the future development of energy system.