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When there is an air gap between the pancake windings in an HTS superconducting magnet, the central magnetic field is increased. To prove the effectiveness of the air gap for increasing the central magnetic field, an HTS magnet with an outsert and an insert magnet was manufactured and tested. The test results proved that the air gap between the pancake windings of the outsert magnet increased the central magnetic field by 11.0%. The critical current of the outsert magnet with the air gap increased by 73.9%. The uniformity of the magnetic field near the center of the magnet also increased. The measured values were compared with the calculated values. [ABSTRACT FROM AUTHOR]

Abstract: The cooling performance and reliability of a transcritical CO2 cycle can be significantly improved by using a multi-stage compressor with gas injection because the CO2 cycle has a large pressure difference across a compressor. The objective of this study is to investigate the performance and operating characteristics of a two-stage CO2 cycle with gas injection. In this study, the performances of a two-stage CO2 cycle with gas injection (called as “two-stage gas injection cycle”) were measured as the amount of refrigerant charge, first- and second-stage compressor frequencies, and first- and second-stage EEV openings were varied in the cooling mode operation. The cooling COP of the two-stage gas injection cycle was maximally enhanced by 16.5% over that of the two-stage non-injection cycle in the experiments. In addition, when the first- and second-stage EEV openings were increased, the compression ratio decreased and this in turn, improved the cooling COP of the two-stage gas injection cycle. However, when the first-stage EEV opening was increased, the mass flow rate through the evaporator decreased, and this in turn, decreased the cooling capacity of the two-stage gas injection cycle. Therefore, in the two-stage gas injection cycle, an optimum control of both EEV openings is required. [Copyright &y& Elsevier]