Research On S-CO₂ Brayton Cycle System Design Optimization Technology

With the advantages of high cycle efficiency,compact structure of system equipment,and clean working fluid,the supercritical carbon dioxide（S-CO₂）Brayton cycle has been considered to be one of the new energy conversion methods that can replace the traditional steam power cycle.And it has gradually become a new generation research hotspots in the field of energy applications.However,the current design and analysis of the S-CO₂ Brayton cycle system and its equipment are relatively independent,and related optimization design is relatively scarce.Therefore,this article has carried out research on the design optimization technology around the S-CO₂ Brayton cycle system and equipment.First,the parameter design and analysis model of the S-CO₂ Brayton cycle system was built and verified,and the preliminary thermal design and evaluation were carried out for the S-CO₂ Brayton energy conversion system with an electric power demand of 1MWe（The maximum and low cycle temperatures are 550℃,32℃,respectively,and the maximum and low pressures are 20MPa,7.69MPa respectively）.At the same time,the influence of the shunt coefficient on the performance of the recompression Brayton cycle system is analyzed,and the system cycle parameters are optimized on this basis.Secondly,the preliminary thermal design and analysis of the key equipment in the proposed 1 MWe recompression Brayton cycle were conducte.Among them,the thesis built and verified the one-dimensional thermal design and analysis model of S-CO₂ turbomachinery,carried out preliminary thermal design of the coaxially arranged turbomachinery,and analyzed the influence of the main geometric structure parameter changes on the performance of the turbomachinery;In addition,the design and analysis models of the S-CO₂ printed circuit board heat exchanger also were built and verified in the paper,and the flow heat transfer model suitable for the semi-circular direct flow channel was used to complete the preliminary designs of the high,low temperature regenerator and precooler in the recompression Brayton cycle.Finally,based on the preliminary thermal design results of the above-mentioned equipment,the paper carried out the corresponding optimization technology research.Among them,with the goal of improving isentropic efficiency,the structure of S-CO₂ turbomachinery was optimized by using the simulated annealing optimization algorithm;at the same time,the influence characteristics of the maximum design working fluid flow rate on the main external dimensions of the heat exchange equipment and the internal working fluid pressure drop are analyzed.The optimal design flow rates of the high-temperature heat exchanger,low-temperature heat exchanger,and precooler were determined respectively,and the design optimization of heat exchange equipment was realized.