| Electrical Energy Storage (EES) technology is the research focus of energy research field. Among all the EES technologies, Compressed Air Energy Storage (CAES) has the merits of wide power range, long life time, unlimited storage time and lower impact on the environment and has become an important research area of current EES technology.CAES system could be divided into two subsystems:the energy storage subsystem and the energy release subsystem. As a key component of energy release subsystem, the operating characteristics of multistage expander directly influence the power output and efficiency of energy storage systems. According to the structure difference, multistage expander could be divided into positive-displacement expander and dynamic expander. Among the former, single valve reciprocating expander, with the merits of simple structure, high pressure ratio and easy controlling, is especially suitable for micro-scale CAES systems. Therefore, this dissertation takes single valve reciprocating expander as the energy release unit of micro-scale supercritical CAES system. Through the methods of theoretical analysis and experimental research, the thermodynamic characteristics of single valve reciprocating expander are discussed, the internal flow fields of expanders are studied and the impacts of different structural and operational parameters on the expander system performance are analyzed. The following aspects are studied in this paper:1. According to the theoretical cycle of single valve reciprocating expander as well as the requirements of micro-scale supercritical CAES systems, thermodynamic design and simulation are conducted, the properties within the cylinder as functions of crank angle and the impacts of different structural and operational parameters on the overall system performance are analyzed, based on which the volume ratio of interstage buffer tanks is optimized.2. CFD numerical computation of the flow field within the cylinders are conducted, the properties as functions of crank angle are studied and the flow fields under different crank angles are obtained, which laid solid theoretical foundation for future flow fields optimization.3. The design method of the air supply system of single valve reciprocating expander is studied, the inlet motion control method is proposed and the air supply system is designed. The design method of expander flywheel is also revised in this paper and the revised design method could compute the flywheel moment more accurately and efficiently. 4. Experimental platform of the single valve reciprocating expander is constructed, the actual operational characteristics are tested and the performance indexes as functions of rotational speed are discussed. Meanwhile, the experimental results are compared with the theoretical results, which provide references for further theoretical and experimental research. |
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