Dynamic simulation of an improved transcritical CO₂ ejector expansion refrigeration cycle

This paper presents a dynamic model of a transcritical CO₂ ejector expansion refrigeration cycle with two-stage evaporation (EERC-TE), which is deemed to further improve the performance of a basic transcritical CO₂ ejector expansion refrigeration cycle (EERC). The adjustments of compressor speed, the expansion valve opening, the throat area of ejector nozzle and the chilled water flow rate of evaporators are conducted as the disturbances to investigate the system transient responses. The presented results show the predictions have a good agreement with the experimental data. The change of compressor speed causes larger response of system parameters than that of the other disturbances. The expansion valve opening can result in obvious variation of the evaporator pressure and the pressure lift ratio of ejector, while the throat area of ejector nozzle leads to outstanding change of the gas cooler pressure and the ejector entrainment ratio. Moreover, these responses are compared with that of EERC and they show the similar change trends. Based on the transient results, the combination adjustment methods are proposed to improve the system performance, and the enhancement of COP of EERC-TE is more distinct and it is 2.58 times than that of EERC under the conditions of this study. In the basis of the transient simulations, flexible and diverse adjustment methods can be applied to improve the system performance and guide the system control.