Performance research on a novel adjustable transcritical CO2 heat pump system with vortex tube expansion

In the transcritical CO2heat pump cycle, the Maurer model using vortex tube expansion instead of conventional throttle valves can reduce the throttling loss and improve the system performance, but the Maurer model has a deficiency in adjustability. By improving the Maurer model, this paper proposes a novel adjustable transcritical CO2heat pump system with vortex tube expansion. A theoretical model is established to simulate and analyse the performance characteristics of the novel system, and the performance is compared with that of the conventional system with expansion valve throttling and the Maurer model. The research shows the results as follows: 1) The novel system can automatically control the heating capacity of the system and the discharge temperature of the compressor. When the evaporation temperature changes, the novel system can control the discharge temperature of the adjusting compressor by varying the opening of the electronic flowrate control valve, and can also control the cold mass fraction and the hot exit temperature of the vortex tube by changing the frequency of the adjusting compressor, thereby adjusting the heating capacity of the system. The novel system brings a high heating capacity and improves performance while ensuring that the hot exit temperature of the vortex tube and the discharge temperature of the compressor do not exceed the warning value of 120 ℃. 2) The performance of the novel system is better than that of the conventional system and the Maurer model. The novel system can obtain a higher heating capacity and better performance by maintaining the hot exit temperature of the vortex tube and the discharge temperature of the adjusting compressor at a high level. When the evaporation temperature varies from -10 ℃ to 10 ℃ throughout the year, the COP and heating capacity of the novel system increase by 13.1% and 16.7% respectively compared with those of the conventional system, and increase by 2.7% and 6.1% respectively compared with those of the Maurer model. The improvement effect of the novel system on system performance will be more significant as the range of evaporation temperature variation expands.