Conference Year
2021
Keywords
ejector performance map, transcritical CO2 cycle, component selection analysis, system modeling
Abstract
Awareness about the climate impact of air conditioning systems has given impetus in developing environment-friendly solutions. The transcritical CO2 cycle with an ejector as a work recovery device has been reported as one of the green solutions in the literature. However, commercial applicability of these systems is limited so far despite their offered potential. One of the major impediments for limited commercial usage is unavailability of a systematic approach for system design that can help system designers in finding the optimum component combination for their application. For materializing system design approach, it is imperative to develop a system model that can accurately predict performance for wide range of operating conditions while considering different possible component combinations. In this paper, an ejector system model is developed using individual component models of ejector, evaporator, and compressor. The ejector is being modeled using the ejector performance maps, a recently developed methodology for representing ejector performance of a fixed-geometry ejector. The ejector performance maps are accurate, yet they can predict ejector performance for wide range of operation. The evaporator is modeled using geometric parameters, and the refrigerant and the air-side operating conditions, whereas other heat exchangers are modeled using thermodynamic state analysis. The compressor is modeled using semi-empirical correlations by curve-fitting ten-coefficient polynomial using compressor speed and pressure ratio as characterizing variables. The system analysis considers a total of eight component combinations for transcritical CO2 ejector cycle and helps in finding the combination that gives the optimum performance. The results are encouraging as the system analysis using ejector performance maps can help in designing new improved systems. The methodology can also be tested for designing ejector air conditioning systems using other refrigerants.