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Journal ArticleDOI

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

06 Mar 2019-Vol. 4, Iss: 1, pp 15
TL;DR: A review of the main developments in ejectors over the last few years can be found in this article, where the main findings and trends in the area of heat-driven ejectors and ejector-based machines using low boiling point working fluids are summarized.
Abstract: 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.
Citations
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01 Jan 2014
TL;DR: In this paper, an analysis of the performance of the ERS using dry and isentropic fluids has been carried out, and the results show that the dry fluids have generally better performance than the wet fluids.
Abstract: Refrigeration systems, air-conditioning units and heat pumps have been recognized as indispensable machines in human life, and are used for e.g. food storage, provision of thermal comfort. These machines are dominated by the vapor compression refrigeration system and consume a large percentage of world-wide electricity output. Moreover, CO2 emissions related to the heating and cooling processes contribute significantly to the total amount of CO2 emission from energy use. The ejector refrigeration system (ERS) has been considered as a quite interesting system that can be driven by sustainable and renewable thermal energy, like solar energy, and low-grade waste heat, consequently, reducing the electricity use. The system has some other remarkable merits, such as being simple and reliable, having low initial and running cost with long lifetime, and providing the possibility of using environmentally-friendly refrigerants, which make it very attractive. The ERS has received extensive attention theoretically and experimentally.This thesis describes in-depth investigations of vapor ejectors in the ERS to discover more details. An ejector model is proposed to determine the system performance and obtain the required area ratio of the ejector by introducing three ejector efficiencies. Based on this ejector model, the characteristics of the vapor ejector and the ERS are investigated from different perspectives.The working fluid significantly influences the ejector behavior and system performance as well as the ejector design. No perfect working fluid that satisfies all the criteria of the ERS can be found. The performance of nine refrigerants has been parametrically compared in the ERS. Based on the slope of the vapor saturation curve in a T-s diagram, the working fluids can be divided into three categories: wet, dry and isentropic. A wet fluid has a negative slope of the vapor saturation curve in the T-s diagram. An isentropic expansion process from a saturated vapor state will make the state after the expansion to fall inside the liquid-vapor area of the T-s diagram which will result in droplet formation. Generally, an isentropic expansion for a dry fluid will not occur inside the liquid-vapor area, and consequently no droplets will form. An isentropic fluid has a vertical slope of the vapor saturation curve in the T-s diagram and an isentropic expansion process will hence follow the vapor saturation curve in the T-s diagram, ideally without any droplet formation. However, when the saturation condition is close to the critical point, it is possible that the isentropic expansion process of a dry fluid and an isentropic fluid occurs inside the liquid-vapor area of the T-s diagram, resulting in formation of droplets. In order to avoid droplet formation during the expansion, a minimum required superheat of the primary flow has been introduced before the nozzle inlet. Results show that the dry fluids have generally better performance than the wet fluids and the isentropic fluid. Hence the thesis mostly focuses on the features of vapor ejectors and the ERS using dry fluids.Exergy analysis has been proven to be very useful to identify the location, magnitude, and sources of exergy destruction and exergy loss, and to determine the possibilities of system performance improvement. This method is applied to the ejector and the ERS. The ejector parameters are closely interacting. The operating condition and the ejector area ratio have a great impact on the ejector overall efficiency and system COP. The ejector efficiencies are sensitive to the operating conditions, and they significantly influence the system performance. A so-called advanced exergy analysis is adopted to quantify the interactions among the ERS components and to evaluate the realistic potential of improvement. The results indicate that, at the studied operating condition, the ejector should have the highest priority to be improved, followed by the condenser, and then the generator.Thermoeconomics, which combines the thermodynamic analysis and economic principles, is applied to reveal new terms of interest of the ERS. The economic costs of the brine side fluids (fluids that supply heat to the generator and evaporator and remove heat from the condenser) play very essential roles in the thermoeconomic optimization of the ERS. Depending on different economic conditions, the system improvement from a thermodynamic point of view could be quite different from the thermoeconomic optimization. The ERS is economically sound when using free heat sources and heat sink.An ejector test bench has been built to test the entrainment ratio of different ejectors. Although the experiments do not achieve the desired results, they could still be discussed. The insignificant effect of the superheat of the secondary flow found in the theoretical study is validated. The assumption of neglecting the velocities at the ejector inlets and outlet are confirmed. The quantification of the ejector efficiencies shows that they largely depend on the operating conditions and the ejector dimensions.

115 citations

Journal ArticleDOI
TL;DR: In this paper, two 1-D ejector mathematical models are used to predict the performance of a solar ejector cooling system with fixed and variable geometry ejectors, and the results showed that the ejector with fixed-geometry was very sensitive to the variations of the operational conditions and could practically be functional only under specific conditions.
Abstract: In the present, study two 1-D ejector mathematical models are used to predict the performance of a solar ejector cooling system with fixed and variable geometry ejectors. Thes models are implemented using MATLAB and EES Software. The effect of the mixing efficiencies on the performance of the system was investigated, and two empirical correlations were obtained using experimental data for an ejector cooling cycle with R141b as a refrigerant. The results obtained with varying efficiencies were found to be significantly more accurate than those obtained with previous models, which assumed a constant efficiency. The results showed that the ejector with fixed-geometry was very sensitive to the variations of the operational conditions and could practically be functional only under specific conditions. It was also found that the solar ejector cooling system with a variable area ejector has higher coefficient of performance under a vast range of operational conditions. The new system could be easily implemented in residential building air conditioning systems with solar energy as the driving source of heat. The refrigerant R134a was found to give the best performance considering operational, safety, and environmental factors. The economic analysis revealed that the new system is profoundly better than the conventional systems in terms of payback period and net present value.

49 citations

Journal ArticleDOI
TL;DR: This paper thoroughly assesses the performance of a CFD model for single-phase ejector simulations and poses precise guidelines to be applied in future research activities and to support the design of ejector-based systems.

41 citations

Journal ArticleDOI
01 Dec 2020-Energy
TL;DR: In this paper, a modified nucleation model was proposed to predict the non-equilibrium condensation phenomenon in a steam ejector of a solar-driven refrigeration system, which can accurately predict the ejector performance.

38 citations

01 Jan 2010
TL;DR: In this paper, the authors examined the interaction of diffracted shock wave pattern and the resulting vortex loop emitted from a shock tube of various geometries, with an ejector having a round bell-shaped inlet.
Abstract: The following cold-flow study examines the interaction of the diffracted shock wave pattern and the resulting vortex loop emitted from a shock tube of various geometries, with an ejector having a round bell-shaped inlet. The focus of the study is to examine the performance of the ejector when using different jet geometries (primary flow) to entrain secondary flow through the ejector. These include two circular nozzles with internal diameters of 15 mm and 30 mm, two elliptical nozzles with minor to major axis ratios of a/b = 0.4 and 0.6 with b = 30 mm, a square nozzle with side lengths of 30 mm, and two exotic nozzles resembling a pair of lips with axis ratios of a/b = 0.2 and 0.5 with b = 30 mm. Shock tube driver pressures of P4 = 4, 8, and 12 bar were studied, with the pressure of the shock tube driven section P1 being atmospheric. High-speed schlieren photography using the Shimadzu Hypervision camera along with detailed pressure measurements along the ejector and the impulse created by the ejector were conducted.

28 citations

References
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Journal ArticleDOI
TL;DR: In this paper, two new two-equation eddy-viscosity turbulence models are presented, which combine different elements of existing models that are considered superior to their alternatives.
Abstract: Two new two-equation eddy-viscosity turbulence models will be presented. They combine different elements of existing models that are considered superior to their alternatives. The first model, referred to as the baseline (BSL) model, utilizes the original k-ω model of Wilcox in the inner region of the boundary layer and switches to the standard k-e model in the outer region and in free shear flows. It has a performance similar to the Wilcox model, but avoids that model's strong freestream sensitivity

15,459 citations

Journal ArticleDOI
TL;DR: In this paper, a 1D analysis for the prediction of ejector performance at critical-mode operation is carried out, where constant pressure mixing is assumed to occur inside the constant-area section of the ejector and the entrained flow at choking condition is analyzed.
Abstract: A 1-D analysis for the prediction of ejector performance at critical-mode operation is carried out in the present study. Constant-pressure mixing is assumed to occur inside the constant-area section of the ejector and the entrained flow at choking condition is analyzed. We also carried out an experiment using 11 ejectors and R141b as the working fluid to verify the analytical results. The test results are used to determine the coefficients, h p, h s, f p and f m defined in the 1-D model by matching the test data with the analytical results. It is shown that the1-D analysis using the empirical coefficients can accurately predict the performance of the ejectors. q 1999 Elsevier Science Ltd and IIR. All rights reserved.

854 citations


"Current Advances in Ejector Modelin..." refers background or methods in this paper

  • ...Others in some cases [70] consider the positioning of the primary nozzle relative to the inlet of the mixing chamber throat, especially in the case of constant area ejectors (Figure 3a)....

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  • ...[70] results for R141b with remarkable success (less than 3....

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  • ...[70] R141b X CPM —Loss coefficients calibrated with experimental data....

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  • ...[70] further proposed a 1D ejector performance analysis based on the CPM principle at choking conditions....

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  • ...[70], which were more accurate than those obtained by sophisticated 1D models for the entrainment ratio in similar conditions....

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Journal ArticleDOI
TL;DR: In this paper, a review of the fundamental characteristics of the shock train and pseudo-shock is presented, and some simple predictions are made to simulate these very complicated phenomena, and control methods of the pseudo-shocks are also described.

478 citations

Journal ArticleDOI

413 citations


"Current Advances in Ejector Modelin..." refers methods in this paper

  • ...The authors attributed this drawback firstly to the ejector inefficiency, designed for single-phase conditions and then to the non-equilibrium effects which were underestimated by the Henry and Fauske [155], approach introduced in their improved model....

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