Energy and exergy analysis of a novel multi-pressure levels ejector absorption-recompression refrigeration system: Parametric study and optimization

Abstract

The world is facing a cooling crunch, and investing in the efficiency enhancement of cooling systems is the most straightforward strategy to mitigate greenhouse gas (GHG) emissions and reduce costs. To this end, this study primarily sought to enhance the efficiency of an absorption refrigeration cycle (ARC) and diminish energy consumption. For this, a vapor compression refrigeration cycle and an ejector-ARC were combined, using a turbo-expander to improve system efficiency. The ejector would be exploited to raise the absorber pressure and reduce pump power, the turbo-expander was employed in place of the expansion valve, and the compressor was partially used to supply generator heat. The proposed system has four pressure levels. The condenser and generator were assumed to be an integrated unit whose heat loss would be used to heat the generator. The effects of several parameters, e.g., generator temperature and pressure, compressor pressure ratio, and ejector parameters, on the coefficient of performance (COP) and exergetic efficiency (ECOP), were explored. The multi-objective optimization showed that the proposed system had much higher performance than the ARC, with up to 191.2% and 54.7% higher COP and ECOP, respectively. Furthermore, the maximum COP occurred at a generator pressure and temperature lower than the ARC. Thus, the proposed design could handle the high activation temperature and pressure challenges of ARCs with an NH3-H2O working fluid. It was also observed that COP was a function of the ejector mixing tube diameter and had a maximum level. The ejector reduced the circulation ratio and increased the absorber pressure above the evaporator pressure, reducing pump power.