Numerical evaluation of ejector-assisted mechanical compression systems for refrigeration applications

• A hybrid and two cascade systems, designed and compared for refrigeration purposes.
• Conjugate effects of the thermal and mechanical compression components interactions on the system performance.
• Existence of an optimum intermediate condition for cascade cycles.
• Effect of the main operating parameters on system performance.

A study of the conjugate effects of ejector performance characteristics, the activation pressure–temperature conditions at the generator and the interaction with the compressor on refrigeration systems was performed. Besides the conventional compression cycle which was used as a reference, three more configurations were selected for this study: a hybrid ejector–compressor booster and two cascade compressor–ejector cycles. The modelling methodology developed to handle such systems was based on the principles of thermodynamics and fluid dynamics and included two separate sub-cycles in constant interaction: a loop driven mechanically by a compressor, coupled with a thermally activated ejector loop. This cycle model was combined with a validated ejector model and manufacturer's compressor performance maps. A performance analysis and a parametric optimization were performed to select promising cycles. For given working conditions, substantial improvement in COP of the selected cycles over the conventional mechanical compression cycle was found.