In this paper, the effects of the two-stage compression with intercooling, ejector expansion, and internal heat exchanger on the transcritical CO_2 refrigeration cycle for air conditioning operation are considered in two moods. The results of the simulation show that in mobile air conditioner where the gas cooler are Air-to-CO_2 heat exchangers, two-stage compression along with ejector-expansion can improve the COP about 27% in compression to the conventional CO_2 refrigeration cycle. In addition, the effect of an internal heat exchanger on the ejector-expansion CO_2 cycle in high ambient temperatures is investigated. The analysis also shows that when Water-to-CO_2 coolers are available; first, the COP could extremely increase; second, using two-stage compression will not have a sensible influence on the COP improvement. Finally, the results also reveal that the operating pressure of the compressor discharge should be somewhat more than the optimum pressure to prevent extreme downfall in the system performance due to the temperature changes.
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