In ejector refrigeration systems, the performance of the ejector is critical to the performance, capability, size and cost of the whole system. Construction of mathematical models has been used as an effective method for analyzing the performance of the ejector as well as the whole refrigeration system. These models can also be used to guide system operation, interpret experimental results and assist in system design and optimization. The overall objective of this paper is to provide a review of various researches of the mathematical model on the hydrodynamic and thermodynamic character within the ejector. The paper first briefly describes ejector including fundamental principle, flowing and mixing mechanism and the method of model establishment. Then various models consisting of ideal assumptions, governing equations, auxiliary conditions, solution methods and main results are presented. The models can be classified into two main categories: (i) steady thermodynamic models which can be further subdivided into single-phase flow model and two-phase flow model and (ii) dynamic models which are also subdivided according to the flowing phases considered. It has been shown that the dynamic models have higher prediction precision and give more information compared with the steady thermodynamic models. In addition, the simplified empirical and semi-empirical models based on measured data are briefly discussed. This review is useful for understanding the evolution process and the current status of the mathematical models on ejector and highlighting the key aspects of model improvement such as the mixing mechanism, the capture of the shock wave, etc.

Progress of mathematical modeling on ejectors

Ejector efficiencies for the primary nozzle, suction, mixing and diffuser were determined for the first time, according to their definitions, using an axi-symmetric CFD model. Water was considered as working fluid and the operating conditions were selected in a range that would be suitable for an air-conditioner powered by solar thermal energy. Ejector performance was estimated for different nozzle throat to constant section area ratios. The results indicated the existence of an optimal ratio, depending on operating conditions. Ejector efficiencies were calculated for different operating conditions. It was found that while nozzle efficiency can be considered as constant, the efficiencies related to the suction, mixing and diffuser sections of the ejector depend on operating conditions.

http://iiiwe.com/file/resume/leilajavadi.pdf

Numerical assessment of steam ejector efficiencies using CFD

A number of factors influence the performance of an ejector. In this work, three geometrical factors – the area ratio between the nozzle and constant area section ( r A ), nozzle exit position (NXP) and constant area section length ( L m ) – were considered. The theoretical analysis was carried out by a CFD model of a steam ejector using FLUENT. The results indicated the existence of an optimal area ratio, depending on operating conditions. Therefore, a new feature, a spindle in the primary nozzle is suggested to fine tune the primary flow rate depending on operating conditions. The location of NXP influenced both entrainment ratio ( λ ) and critical back pressure ( p c,crit ), showing an optimum at 60 mm from the inlet plane of the ejector mixing section. L m had little influence on λ ; however, longer constant area sections resulted in higher p c,crit . For an optimal design, a value of L m  = 155 mm was identified.

Influence of geometrical factors on steam ejector performance – A numerical assessment

Design aspects of ejectors: Effects of suction chamber geometry

Ejectors used in refrigeration systems as entrainment and compression components or expanders, alone or in combination with other equipment devices, have gained renewed interest from the scientific community as a means of low temperature heat recovery and more efficient energy use. This paper summarizes the main findings and trends, in the area of heat-driven ejectors and ejector-based machines, using low boiling point working fluids, which were reported in the literature for a number of promising applications. An overall view of such systems is provided by discussing the ejector physics principles, as well as a review of the main developments in ejectors over the last few years. Recent achievements on thermally activated ejectors for single-phase compressible fluids are the main focus in this part of the review. Aspects related to their design, operation, theoretical and experimental approaches employed, analysis of the complex interacting phenomena taking place within the device, and performance are highlighted. Conventional and improved ejector refrigeration cycles are discussed. Some cycles of interest employing ejectors alone or boosted combinations are presented and their potential applications are indicated.

https://www.mdpi.com/2411-5134/4/1/16/pdf

Current Advances in Ejector Modeling, Experimentation and Applications for Refrigeration and Heat Pumps. Part 1: Single-Phase Ejectors

Hydrodynamic aspects of ejectors

In the present work, computational fluid dynamics (CFD) studies on single phase turbulent confined jets were carried out. The CFD model was validated by comparison with a number of parameters available from the previous literature. An attempt is made to study the jet expansion and hydrodynamics in presence of confinement. This has been studied in two ways: (i) effect of enclosure size and (ii) effect of presence of draft tube. The effect of enclosure size was investigated over a wide range and compared with the previous literature. It was observed that with an increase in the draft tube diameter, the entrainment rate of the surrounding fluid into the draft tube increases while the average turbulent kinetic energy in the jet flow in draft tube decreases. Thus the size of the draft tube plays an important role in determining the level of entrainment and the extent of mixing between the jet fluid and the surrounding fluid.

M.T. Kandakure

Papers

Hydrodynamic aspects of ejectors

Characteristics of turbulent confined jets