Abstract
Trans-critical CO2 vapor compression (VC) refrigeration cycles require a high compression ratio, which is associated with high expansion losses. To recover these expansion losses, a pressure exchange process between the low- and high-pressure sides of the VC cycle is proposed and examined in this study. The proposed pressure exchange system is an open type constant volume process where the high- and low-pressure flows mix inside the system. This prototype is inspired by the pressure exchangers used in reverse-osmosis (RO) desalination systems. In this system, a 2D model was generated and modeled using the computational fluid dynamics (CFD) technique. The numerical model ignored any losses due to leakage or hydraulic friction and the process is considered adiabatic. For the modeling, it was assumed that the inlet conditions for the two pressure exchanger flows are similar to the flow conditions at the evaporator and gas cooler outlets in a VC cycle. Two parameters are examined to test the validity of the system and understand their effect on the performance, including the inlet flow rate represented by the inlet velocity and the process time represented by the speed of rotation. A total of nine cases were simulated and analyzed in this study.
Highlights
Global warming and its detrimental effects on the planet have forced action among scientists, politicians, and the general public
The influence of the pressure and temperature boundary conditions are not considered in this study, while the focus is on understanding the system behavior under different rotational speed and flow rate conditions
A computational fluid dynamics (CFD) model of a pressure exchange device was generated to investigate the concept of recovering momentum energy for carbon dioxide inside a trans-critical refrigeration cycle
Summary
Global warming and its detrimental effects on the planet have forced action among scientists, politicians, and the general public. The major challenges associated with using CO2 as a refrigerant are its low critical temperature and high operating pressure. This leads to lower system performance at warmer ambient conditions and higher expansion losses, respectively. The refrigerant from the medium-temperature compressors enters a gas cooler/condenser and rejects heat to the surroundings. The refrigerant exiting the gas cooler/condenser is expanded through a high-pressure expansion valve before entering a flash tank for phase separation. After absorbing heat from the low-temperature loads, the low-temperature refrigerant is superheated by passing through the flash tank before being compressed in the low-temperature compressors. The low-temperature compression outlet mixes with medium-temperature refrigerant before both streams are compressed in the medium-temperature compressors
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
