Abstract
In this study, the performance of an ejector refrigeration system using HCFO-1233zd(E) as the working fluid is investigated and presented. A novel improved modeling approach that considers ejector loss coefficients as functions of the ejector pressure lift and area ratio has been used. The resulting mathematical model developed using the first and second laws of thermodynamics and gas dynamics is solved using Engineering Equation Solver. Different ejector geometries with area ratios of 6.44, 7.04, 7.51, 7.73, 8.28, 8.62, 9.13, 9.41 and 10.64 were used in this study. The evaporator temperatures were between 0 °C and 16 °C, the generator temperatures were between 75 °C and 120 °C and the condensing temperatures varied between 20 °C and 40 °C. For the range of parameters used, the optimal coefficient of performance (COP) is in the range 0.11 and 0.88 for evaporator temperatures between 4 °C and 16 °C. At the optimal working conditions, the COP improves with higher area ratios, lower condensing temperatures and requires increased generator temperatures. In the critical mode of operation, both the energetic and exegetic performance of the ejector are shown to decline as generator temperatures increase, evaporator temperatures reduce and as the area ratios decrease. Thermodynamic investigation using the exergy analysis method indicates that most of the exergetic losses come from the ejector (46-56%) followed by the condenser (18-29%), the generator (21-26%), the evaporator (0.8-3%), and the throttle valve (1- 1.6%), with the pump having a very small contribution. Moreover, correlations for the optimal generator and optimal COP were derived and presented. Keywords: Coefficient of performance, Critical mode, Ejector refrigeration system, Ejector loss coefficients, Exergetic performance, Hydroflouroolefins
Highlights
IntroductionAccess to modern energy services remains an important factor as both developed and developing nations strive to achieve increased industrialization, increased economic growth and better standards of living
The current HVAC&R systems rely mainly on the vapor compression cycle powered by electrical energy generated largely from fossil fuels, and they require working fluids, most of which possess significant global warming potential (GWP)
Results for all the considered ejectors have been used in the derivation of correlations for optimal coefficient of performance (COP) and optimal generator temperatures, to present results concisely, only ejectors AA, 3, 4, AC, 1 and EH with area ratios of 6.44, 7.04, 7.51, 8.28, 9.13 and 10.64, respectively, have been used to generate figures for the detailed discussion in the succeeding sections
Summary
Access to modern energy services remains an important factor as both developed and developing nations strive to achieve increased industrialization, increased economic growth and better standards of living. The current HVAC&R systems rely mainly on the vapor compression cycle powered by electrical energy generated largely from fossil fuels, and they require working fluids, most of which possess significant global warming potential (GWP). With these challenges, research efforts in HVAC&R are focused on developing systems that use sustainable, clean and renewable energy resources as well as systems that use working fluids that are not detrimental to the environment. The ejector refrigeration system is one of these systems that has shown potential as a simple, low cost and highly durable system It does not have any moving parts and can be activated by readily available low grade heat sources (Martel and Parakh, 2015). Only the primary flow is choked, and performance reduces with increasing backpressure
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