Coupled design and optimization of the turboexpander-compressor for full-range high efficiency in reverse brayton cycles.

As an environmentally benign natural refrigerant, air has emerged as a promising alternative for sustainable refrigeration systems, where the expander-compressor performance represents the critical limiting factor. This paper proposes a coupled design method for compressors and expanders in air refrigeration cycles, featuring identical pressure ratios, flow similarity, and high-efficiency operation across all working conditions. The imperialist competitive algorithm was implemented with annual system efficiency as the objective function to optimize the turboexpander-compressor. Experimental validation confirms the accuracy of the one-dimensional loss model and computational fluid dynamics simulation, demonstrating the feasibility of the proposed methodology. Under summer conditions of Beijing (2023), the designed system achieves an average turboexpandercompressor system efficiency of 2.759. Results indicate that the ratio of pressure ratio between the compressor and expander remains within 0.9–1.05, satisfying the identical pressure ratio design requirement. The system maintains high efficiency even under peak cooling demand, effectively mitigating performance degradation in high-load scenarios.