Experimental study on the performance of an auto-cascade refrigeration system integrating fractional condensation and flash separation

In auto-cascade refrigeration systems, low vapor-liquid separation efficiency reduces the refrigerant flow rate within the evaporator, diminishing the cooling capacity. This paper presents an innovative approach integrating fractional condensation and flash separation to enhance the refrigerant flow rate in the evaporator and the evaporation pressure. This study experimentally investigates the steady-state operation and on-off performance of the modified system. The energy efficiency comparison is conducted under varying cabinet temperatures and ambient temperatures. The effect mechanism of flash pressure is analyzed in detail. Results indicate that coupled separation boosts the refrigerant flow rate and the concentration of high boiling point compositions in the evaporator. Within a range of cabinet temperature variations, the refrigeration capacity and energy efficiency are enhanced by 5.25 %–11.36 % and 5.29 %–9.88 %. The energy consumption within 24 h decreases by 2.38 %–19.99 %. Under varying ambient temperatures, the cooling capacity and energy efficiency exhibit average growth rates of 8.21 % and 7.28 %. The energy consumption within 24 h is saved by 5.91 %–2.22 %. The decrease in flash pressure reduces the refrigerant flow rate but increases the concentration of low-boiling point compositions in the evaporator. The increase in throttling effect of the mixed refrigerant contributes to an enhancement in refrigeration capacity and COP, with values rising from 132.77 W to 146.74 W and from 0.341 to 0.381. Compared with the conventional system, the refrigeration capacity and COP are improved by 22.02 % and 14.58 %. The optimization of the separation process of the novel system provides an experimental foundation for improving the performance of auto-cascade refrigeration systems.