The increasing need for thermal comfort has led to a rapid increase in the use of cooling systems and, consequently, electricity demand for air-conditioning systems in buildings. Heat-driven ejector refrigeration systems appear to be a promising alternative to the traditional compressor-based refrigeration technologies for energy consumption reduction. This paper presents a comprehensive literature review on ejector refrigeration systems and working fluids. It deeply analyzes ejector technology and behavior, refrigerant properties and their influence over ejector performance and all of the ejector refrigeration technologies, with a focus on past, present and future trends. The review is structured in four parts. In the first part, ejector technology is described. In the second part, a detailed description of the refrigerant properties and their influence over ejector performance is presented. In the third part, a review focused on the main jet refrigeration cycles is proposed, and the ejector refrigeration systems are reported and categorized. Finally, an overview over all ejector technologies, the relationship among the working fluids and the ejector performance, with a focus on past, present and future trends, is presented.

https://re.public.polimi.it/bitstream/11311/984261/1/2016_RSER_BesagniMereuInzoli.pdf

Ejector refrigeration: A comprehensive review

This study presents experimental results obtained from a transcritical R744 system using a refrigerant ejector. The results were compared to that of a conventional system with an expansion valve. For the test conditions considered, the cooling capacity and COP simultaneously improved by up to 8% and 7%, respectively. Experiments were analyzed to quantitatively assess the effects on system performance as a result of changes in basic ejector dimensions such as motive nozzle and diffuser sizing. Small angles of 5° yielded best results for the static pressure recovery of the high-speed two-phase flow entering the diffuser. Experiments confirmed that like in a conventional transcritical R744 system with expansion valve, the high-side pressure control integrated into the ejector could be used to maximize the system performance. Numerical simulation results helped identifying this basic trend. Due to difficulties in the ejector throat pressure measurements, a more practical performance metric was introduced in order to quantify overall ejector efficiencies. According to this definition, the prototype ejector was able to recover up to 14.5% of the throttling losses.

Experimental validation of a prototype ejector designed to reduce throttling losses encountered in transcritical R744 system operation

The present paper provides a literature review on two-phase ejectors and their applications in vapor compression refrigeration and heat pump systems. Geometry, operation and modeling of ejector, and effects of various operating and geometric parameters, and refrigerant varieties on the ejector performances as well as performance characteristics of both subcritical and transcritical vapor compression systems with various cycle configurations are well-summarized. Moreover, system optimal operation and control to get maximum performance by using ejector as an expansion device are also discussed. However, a lot of research work still needs to be done for large-scale applications in industry and for the replacement/modification of conventional refrigeration and heat pump machines. Favorable performance improvement along with several advantages in installation, operation and control with ejector stimulates the commercialization of ejector enhanced refrigeration and heat pump systems and hoping this contribution will be useful for any newcomer in this field of technology.

Ejector enhanced vapor compression refrigeration and heat pump systems—A review

This paper aims at providing a literature review on the recent development in ejectors, applications of ejector refrigeration systems and system performance enhancement. The paper presents useful guidelines regarding background and operating principles of ejector. A number of studies are reported and categorized in several topics including, refrigerant selections, mathematical modelling and numerical simulation of ejector system, geometric optimizations, operating conditions optimizations and combinations with other refrigeration systems. Most of the works that have been carried out recently are still limited to computer modelling, more experimental and large-scale work are needed in order to provide better understanding for the real industrial application.

Recent developments in ejector refrigeration technologies

This paper presents a useful knowledge of ejector working principles and the versatility and diversity of its applications in refrigeration technologies. Various ejector refrigeration systems are described with the associated studies, and categorized as conventional ejector refrigeration system, advanced ejector refrigeration systems, combined refrigeration systems and ejector enhanced vapor compression systems. This paper also presents the important elements that affect the optimum performance of the ejector system, and the results of studies that have generally confirmed their energy saving, great potential for large refrigerating temperature scales and performance enhancement.

Wei Lu

Papers

Particular characteristics of transcritical CO2 refrigeration cycle with an ejector