Evaluation and analysis on the coupling performance of a high-speed turboexpander compressor

•The TEC overall efficiency could be used to evaluate the TEC overall performance.•ηTEC is more suitable to reflect the TEC’s coupling performance than ηT.•The TEC overall efficiency could reach 67.2%.•22.3% of the energy output by the expander was recycled.•For a TEC, the expander efficiency should be fully utilized first. A high-speed turboexpander compressor (TEC) for small reverse Brayton air refrigerator is tested and analyzed in the present work. A TEC consists of an expander and a compressor, which are coupled together and interact with each other directly. Meanwhile, the expander and compressor have different effects on the refrigerator. The TEC overall efficiency, which contains effects of the expander's expansion, the compressor's pre-compression, and the pressure drop between them, was proved. It unifies influences of both compression and expansion processes on the COP of refrigerator and could be used to evaluate the TEC overall performance. Then, the coupling parameters were analyzed, which shows that for a TEC, the expander efficiency should be fully utilized first, followed by the compressor pressure ratio. Experiments were carried out to test the TEC coupling performances. The results indicated that, the TEC overall efficiency could reach 67.2%, and meanwhile 22.3% of the energy output was recycled.