Exergetic Efficiency of the Ejector Operating Across Ambient Temperature in a Combined Power and Ejector-refrigeration Cycle

orc2019 Tracking Number 15

Exergy analysis became a standard method for efficiency assessment and optimization of thermodynamic systems and their components. An extensive literature review reveals that exergetic efficiency is often open to individual interpretations which leads to several coefficients of exergy efficiency such as the input-output efficiency, the consumed-produced efficiency and fuel-product efficiency [1]. Serious shortcomings of the aforementioned efficiency definitions while applying to the expansion and compression processes operating across or below ambient temperature were revealed by Sorin and Khennich [2]. They have also recently presented a definition of the coefficient of exergy efficiency for components based on the concept of transiting exergy, i.e. the part of the exergy that has been unaffected within an analysed process. The transiting exergy concept provides unique definitions of the exergy produced and exergy consumed in a process operating across or below ambient temperature and the exergetic efficiency as a result of the ratio between these values. The main objective of this research is to determine the exergetic efficiency of the components of a combined power and ejector-refrigeration cycle with focus on the single-phase ejector operating across ambient temperature and its effects on the overall exergetic efficiency of the system. The system is a combination of Organic Rankine Cycle and ejector-based refrigeration. A fraction of fluid entering the turbine is withdrawn and enters the ejector as its primary flow. The remaining flow in the turbine expands further and is mixed with the outlet of the ejector (the latter is the sum of primary flow and the entrained stream coming from the evaporator) [3]. In this research, the effects of operating conditions of the ejector, i.e. the pressure and mass flow rate of the primary flow, the pressure of the evaporator and the pressure of condenser (back pressure) on the exergetic efficiencies of the ejector and the overall system have been investigated. The link between the efficiency of the overall system and the exergetic (transiting) efficiency of the ejector is established. [1] D. Marmolejo-Correa and T. Gundersen, “A comparison of exergy efficiency definitions with focus on low temperature processes,” Energy, vol. 44, no. 1, pp. 477–489, 2012. [2] M. Sorin and M. Khennich, “Exergy Flows Inside Expansion and Compression Devices Operating below and across Ambient Temperature,” in Energy Systems and Environment, vol. 2, InTech, 2018, p. 64. [3] A. Habibzadeh, M. M. Rashidi, and N. Galanis, “Analysis of a combined power and ejector-refrigeration cycle using low temperature heat,” Energy Convers. Manag., vol. 65, pp. 381–391, 2013.