Optimal heat rejection pressure for transcritical CO₂ refrigeration cycle with an expander

ABSTRACT

Heat rejection pressure plays an important role in designing a transcritical CO₂ refrigeration system, and it has an optimal value to maximize the system’s coefficient of performance (COP). With a thermodynamic simulation model, the optimal heat rejection pressure is studied in the paper for an expander cycle, as well as conventional throttle valve cycle. The effects of compressor efficiency, expander efficiency, gas cooler outlet temperature, and evaporation temperature on the optimal heat rejection pressure are analyzed. It is the first time for a transcritical CO₂ expander cycle that the optimal heat rejection pressure is correlated with the gas cooler outlet temperature and the evaporation temperature at given compressor efficiency and expander efficiency. The average deviation from the correlation to simulation results is less than 1.0%. The correlation provides a guideline to system development and performance optimization of a transcritical CO₂ expander cycle.

KEYWORDS:

• Expander
• optimal heat rejection pressure
• simulation
• transcritical CO₂ cycle

Funding

The authors acknowledge the support by the National Natural Science Foundation of China under Grant 50676064 and the Tianjin Natural Science Foundation of China under Grant 10JCYBJC08300.

Additional information

Funding

The authors acknowledge the support by the National Natural Science Foundation of China under Grant 50676064 and the Tianjin Natural Science Foundation of China under Grant 10JCYBJC08300.