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.

A review on versatile ejector applications in refrigeration systems

Particular characteristics of transcritical CO2 refrigeration cycle with an ejector

The heat and mass transfer in an unsaturated wet cylindrical porous bed packed with quartz particles was investigated theoretically for relatively low convective drying rates. Local thermodynamic equilibrium was assumed in the mathematical model describing the multi-phase flow in the unsaturated porous media using the energy and mass conservation equations to describe the heat and mass transfer during the drying. The drying model included convection and capillary transport of the free water, diffusion of bound water, and convection and diffusion of the gas. The numerical results indicated that the drying process could be divided into three periods, the temperature rise period, the constant drying rate period and the decreasing drying rate period. The numerical results agreed well with the experimental data verifying that the mathematical model can evaluate the drying performance of porous media for low drying rates. The effects of drying conditions such as the ambient temperature, the relative humidity, and the velocity of the drying air, on the drying process were evaluated by numerical solution.

Numerical and experimental investigation of convective drying in unsaturated porous media with bound water

A model on heat and mass transfer in unsaturated porous media with solid/liquid phase change was developed with extending the three-variable model previously proposed. The movement of air phase and its effect on the motion of water is considered. The model has been checked with comparison of the experimental results of the temperature distribution for two dimensional freezing process. The evolution of air pressure, water and ice saturation were predicted by solving the governing equations. The ice segregation and moisture movement toward the front of freezing were numerically simulated.

Tao Lu

Papers

Particular characteristics of transcritical CO2 refrigeration cycle with an ejector

Numerical and experimental investigation of convective drying in unsaturated porous media with bound water

Heat and mass transfer in unsaturated porous media with solid–liquid change