Evaluation of CO2-doped blends in single-stage with IHX and parallel compression refrigeration architectures

Abstract

CO2 is the standard for medium to large-sized commercial applications, as it combines security and low environmental impact. However, it requires the use of advanced and complex cycles. Recently, CO2-doping (the addition of a small quantity of another fluid) has attracted scientific attention, as when CO2 is mixed with fluids with higher critical temperatures, the optimum operation moves to subcritical, providing COP increments in relation to pure-CO2 operation. This work, from a theoretical perspective, evaluates CO2-doping with the fluids R-152a, R-1234yf, R-1234ze(E) and R-1233zd(E) considering the two most used CO2 cycles: the base cycle with an internal heat exchanger (IHX) and the cycle with parallel compression (PC), fractionation taking place. The work analyses the COP improvements for an evaporating level of -10 °C and from 10 to 40 °C of environment temperature. Predicted maximum COP increments reach up to 5.8% for the IHX cycle and 10.0% for the PC cycle.