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Three-dimensional invisible finned-tube is a kind of high-efficiency enhanced tube which is widely used at present. In order to study and analyze advantages and disadvantages of heat transfer and flow performance of the three-dimensional invisible finned-tube, other enhanced tube heat exchangers are introduced and compared through experiments. After analysis and research, it is found that the total heat transfer coefficient K is not the only indexes for evaluating the performance of the heat exchanger, and the resistance is also one of the indexes. According to the evaluation standard of the comprehensive performance of the heat exchanger, the comprehensive performance factor η of the tube side and shell side of the three-dimensional invisible finned-tube heat exchanger is better than that of the other enhanced tube heat exchanger, and the enhanced tube standard is reached under certain conditions, which shows that the three-dimensional invisible finned-tube heat exchanger has excellent performance. The analysis results in this paper have certain guiding significance for engineering design and application of three-dimensional invisible finned-tube heat exchanger.

A single cylinder rotary compressor was applied in the refrigerant injection air-source heat pump to improve the heating performance in cold regions. In this study, the performance of an R410A single cylinder rotary compressor vapor injection (SCRCVI) system was measured and analyzed by varying the compressor frequency f and injection pressure Pinj at the ambient temperature Tod=–10°C.The experimental results indicated that an optimum injection pressure to gain the maximum COPh (coefficient of performance) existed in the SCRCVI cycle. However, the maximum COPh of the SCRCVI system decreased as the increase of the frequency, and the maximum COPh was even lower than that of the CSVC system at high compressor frequency. Therefore, in view of the energy saving and emission reduction, the SCRCVI system should be switched to single stage compression system when the heating capacity demand could be satisfied at high compressor frequency f. Compared to the conventional single-stage vapor compression (CSVC) system, refrigerant injection could enhance the heating capacities and COPh by 28.2% and 7.91%, respectively. The average total mass flow rate of the SCRCVI system was 24.68% higher than that of the CSVC system. As the SCRCVI system worked at the optimum injection pressure, the variation trends of the different system parameters were investigated in detail. These trends were reliably used to optimize the refrigerant injection system design and the control strategy. The parameter of (Pinj–Ps) could be adopted as the signals to control the opening of the upper stage electronic expansion valve EEV1.

Applying the refrigerant injection technology to air-source heat pump had been proved to be an effective access to acquire a better performance in the cold regions. In this paper, the test-bed of R410A single-cylinder rotary compressor vapor injection (SCRCVI) system with flash tank was built and measured by changing the compressor frequency f and injection pressure Pinj under various ambient temperatures. The experimental results indicated that the effect of refrigerant injection became stronger as the ambient temperature decreased. So the SCRCVI showed a superior heating performance at lower ambient temperature, and the conventional single-stage vapor compression (CSVC) system would exhibit higher COPh, while the ambient temperature was beyond the critical value. Compared with the CSVC system, the Qh and COPh were improved by 9.1 ~ 29.5 and 5.35 ~ 7.89%, respectively, under the ambient temperature Tod = − 10 °C. The injection pressure ratio Rp under different operating conditions was varied in the range between 0.2 and 0.22. Specifically, the trend in variation of Rp was reliably used to optimize the refrigerant injection system design and the control strategy.