A critical review linking ejector flow phenomena with component- and system-level performance

This paper provides a critical review of ejector technology for chiller applications, combining an understanding of ejector fluid flow fundamentals with cycle applications. An ejector is a passive momentum-transfer device that requires no external mechanical input or moving parts. The progression of studies on ejectors from the early 1940s to the present from analytical and numerical modeling to visualization studies of the ejector itself is discussed. Included is an assessment of the most recent computational models. Suggestions for future research include improved computational modeling of shock phenomena and the effects of two-phase flow in ejectors. Application of ejectors in chillers is also reviewed, with an emphasis on the basic ejector-based chiller cycle and the development of passive systems that require zero mechanical input for operation. Important connections are made between ejector component- and system-level studies that would together lead to improved overall system performance.     

Performance comparison of fixed- and controllable-geometry ejectors in a CO2 refrigeration system

This paper presents a performance comparison of fixed- and controllable-geometry ejectors equipped with convergent and convergent-divergent nozzles installed in a CO₂ refrigeration system. The coefficient of performance (COP) of an ejector-based refrigeration system depends on the control of the mass flow rate through the device. Thus, two different solutions were analysed, i.e., ejectors with fixed and controllable geometries. A set of fixed-geometry ejectors working in parallel provides incremental regulation of the refrigerant flow, whereas a controllable-geometry ejector with a needle provides more flexible regulation of the mass flow rate. To compare the potential of both approaches, the device performance was numerically simulated using a validated homogeneous equilibrium model (HEM) for the same typical transcritical parameters. For the fixed-geometry ejectors, the performances of devices of various sizes were simulated and compared with the corresponding controllable-geometry ejector performances at several needle positions. For both ejector types, the global efficiency as a function of the mass flow rate is presented and discussed. The results show that each fixed-geometry ejector configuration exhibits high efficiency over the entire range of operating conditions. In the case of the controllable-geometry ejectors, the efficiency is even higher for a reduction in the motive nozzle throat area of up to approximately 35%, after which the efficiency gradually decreases.     

Novel ejector model for performance evaluation on both dry and wet vapors ejectors

A novel ejector model is proposed for the performance evaluation on ejectors with both dry and wet vapor working fluids at critical operating mode. A simple linear function is defined in order to approach the real velocity distribution inside the ejector. Mass flow rates of the primary flow and secondary flow are derived by integrating the velocity function at the inlet section of the mixing chamber. By considering the flow characteristics of the critical-mode operating ejector, the developed model contains only one energy conservation equation and is independent of the flow in the mixing chamber and the diffuser. Experimental data from different ejector geometries and various operation conditions reported earlier are used to verify the effectiveness of the new model. Results show that the model has a good performance in predicting the mass flow rates and the entrainment ratio for both dry and wet vapor ejectors.     

低温流体流动可视化研究综述

低温流体在航天、医疗设备、大型超导实验装置以及工业过程等领域的应用正变得越来越多,而可视化是对低温流体的紊流和两相流体动力学等复杂流动现象进行研究的重要手段。对低温流体流动可视化研究使用的一些最新方法和技术进行了介绍,着重对不同低温流体流动可视化技术的原理与应用场合、实验系统的光学部件与设备要求、可视化观察的典型图像结果作了总结。     

An experimental investigation of an ejector for validating numerical simulations

Supersonic ejectors have been used in cooling/refrigeration applications since the early 1900s. Interest in supersonic ejectors has been rekindled by recent efforts to reduce energy consumption; ejector refrigeration systems can be powered by solar energy or by waste heat generated by another process. This paper describes an experimental test bench using R245fa that was assembled and operated at CanmetENERGY in Varennes. The results from this test bench provide a source of reference data that may be used to validate numerical models of ejectors that could be used in refrigeration applications. Limited results from two numerical models are presented for comparison; global results from a 1D model and results from a detailed CFD model that show the flow field inside the ejector.     

CFD analysis of ejector in a combined ejector cooling system

One-dimensional ejector analyses often use coefficients derived from experimental data for a set of operating conditions with limited functionality. In this study, several ejector designs were modelled using finite volume CFD techniques to resolve the flow dynamics in the ejectors. The CFD results were validated with available experimental data. Flow field analyses and predictions of ejector performance outside the experimental range were also carried out. During validation, data from CFD predicted the entrainment ratios with greater accuracy on definite area ratios, although no shock was recorded in the ejector. Predictions outside the experimental range—at operating conditions in a combined ejector–vapour compression system—and flow conditions resulting from ejector geometry variations are discussed. It is found that the maximum entrainment ratio happens in the ejector just before a shock occurs and that the position of the nozzle is an important ejector design parameter.     

Piezoelectrically actuated flextensional micromachined ultrasound droplet ejectors

This paper reports a variation on the design of the flextensional transducer for use in ejecting liquids. The transducer is constructed by depositing a piezoelectric thin film to a thin, edge-clamped, circular annular plate. By placing a fluid behind one face of a vibrating compound plate that has an orifice at its center, we achieve continuous or drop-on-demand ejection of the fluid. We present results of ejection of water and isopropanol. The ejector is harmless to sensitive fluids and can be used to eject fuels as well as chemical and biological samples. Micromachined two-dimensional array piezoelectrically actuated flextensional droplet ejectors were realized using planar silicon micromachining techniques. Typical resonant frequency of the micromachined device ranges from 400 kHz to 4.5 MHz. The ejection of water through a 5-μm diameter orifice at 3.5 MHz was demonstrated by using the developed micromachined two-dimensional array ejectors     

Review of recent developments in advanced ejector technology

Previous reviews on ejectors for expansion work recovery have provided detailed discussions of operating characteristics and control of ejector cycles, zero-dimensional ejector modeling, ejector geometry effects, and alternate ejector cycles. However, important advances in the field of ejector technology have occurred since previous reviews were written. Several focuses of recent ejector research are the development of multi-dimensional CFD ejector models, investigation of alternate ejector cycles and uses of the work recovered by the ejector, implementation of effective control strategies for ejector cycles, and application of ejectors in real systems. The objective of this paper is to present a review of developments in the use of ejectors for expansion work recovery in vapor-compression systems focusing on the past several years. Although the first commercial applications are being introduced to the market, it is suggested that future works continue in these areas in order to make ejectors more suitable for additional applications.     

Diode-laser-based near-resonantly enhanced flow visualization in shock tunnels

Two new near-resonantly enhanced flow visualization techniques suitable for hypersonic low-density flows in shock or arc tunnels have been developed using seeded lithium (Li) metal as the refractivity-enhancing species. Two semiconductor lasers, single-longitudinal-mode and multimode, are compared with respect to their suitability as light sources for the technique. Transient wake-flow structures around a cylinder and a model of a planetary entry vehicle are visualized to demonstrate the capabilities of this comparatively inexpensive and simple visualization system. The images show flow features which are undetectable with conventional schlieren, shadowgraph, or interferometry techniques. Furthermore, the effect of density inhomogeneities along the line-of-sight outside the region of interest can be reduced by enhancing the refractivity only in selected parts of the flowfield.     

水蒸汽喷射泵系统实用设计软件的开发

本文在Turboc环境下开发了多级蒸汽喷射泵系统的设计软件，该软件包括了压缩比优化分配、单级喷射泵结构尺寸设计和冷凝器的结构尺寸设计等内容，使设计人员能够根据具体的工艺条件，快速地完成多级喷射泵系统的设计，对于提高多级喷射泵系统的工作稳定性、节省能源具有实际意义。     

基于Java3D的空间关联规则可视化原理与实现

空间数据挖掘可视化是空间数据挖掘研究的一个重要方面。可视化技术充分利用了图形和图像的表达能力以及人对于色彩和空间的敏锐的感知能力,使人机有机地融合在一起。本文在简述空间关联规则可视化基本需求的基础上,提出了空间关联规则可视化的一般方法,并进行用Java3D技术开发空间关联规则可视化工具的应用研究。重点在于分析利用Java3D技术进行空间关联规则可视化的基本原理和方法,并给出核心部分流程。最后将该技术应用于两个具体实例中,并给出实现的空间关联规则可视化界面。     

On the design of deep-hole drills with non-traditional ejectors

This work deals with the development of design criteria for deep-hole drills with non-traditional ejectors of circular and plain type. An analytical method for design on non-traditional ejectors with circular jet was developed. The experimental investigation of the developed method was found suitable for the design of single lip non-traditional ejector gundrills of bigger diameter. For smaller diameter drills the results were not satisfactory. For smaller diameter size gundrills the equations analytically developed were modified to suit the experimental results. Further investigation of these modified equations found them to be appropriate. In the case of plain type ejectors, the design methods were developed based on experimental results since this type of ejector does not lend itself easily to theoretical analysis.     

Numerical investigation of a two-phase CO2 ejector

Using an ejector as an additional component in a vapor compression refrigeration system is a promising way to increase the system efficiency. The efficiency increase of the refrigeration system depends strongly on the ejector. Using CFD simulations, it is possible to obtain a better understanding of two-phase CO₂ ejectors in order to design more efficient ejectors. In this work, a numerical model based on a homogeneous equilibrium approach, which is implemented in OpenFOAM, is used to simulate the CO₂ ejector. The numerical investigation of an ejector operated with and without a suction mass flow is presented and the numerical results are compared to experimental data published in previous works to validate the simulations. If the ejector is operated without a suction flow, no mixing losses occur and the friction losses are one of the main losses affecting the flow. Thus, this operating condition is suitable to validate if the friction losses are determined correctly by the numerical model. Afterwards, an ejector which is operated with a suction flow is simulated in order to validate the accurate prediction of the mixing losses by the numerical model. In the presented data range, the numerical model predicts the driving mass flux within an error margin of 10%. The pressure recovery of the ejector operated without a suction flow is determined with an error of 10%. This error increases to 20% when the ejector is operated with a suction flow.     

旋转式压缩机气流噪声研究综述和展望

回顾了旋转式压缩机气流噪声理论与应用的国内外研究现状。对气流噪声研究情况进行分类评述：储液器内气流噪声研究，涉及到计算方法和试验设计分析；排气阀的研究，包括流固耦合分析模型和可视化试验；消声器的研究，包括声学理论分析、试验技术和降噪改进方法；压缩机腔体内气流噪声研究，主要集中在声源识别，简化的集总参数模型和基于CFD的声学分析等3个方面。最后讨论了目前研究存在的一些问题和今后的研究方向。     

Irregular flows

Irregular flows were examined by means of flow visualization methods and hot-wire techniques. When the Reynolds number is small the flow is steady and regular. As the Reynolds number increases, however, the flow becomes irregular. It seems that at large Reynolds numbers the flow generally consists of many structures which fluctuate irregularly. As yet the mechanism by which irregularities occur is not clear.     

A 1-D analysis of ejector performanceAnalyse unidimensionnelle de la performance d'un éjecteur

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, η_p, η_s, φ_p and φ_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.     

Hybrid method combining orthogonal projection Fourier transform profilometry and laser speckle imaging for 3D visualization of flow profile

This paper reports a straightforward technique for three-dimensional (3D) visualization of a flow profile by a hybrid algorithm combining Fourier transform orthogonal fringe projection and laser speckle imaging techniques. The use of orthogonal projection aims to suppress the zero order allowing surface reconstruction with high spatial resolution and accuracy while analyzing the intensity fluctuations of diffuse backscattered laser light providing 2D flow information. Once both are achieved, 3D flow visualization can be displayed. The method is experimentally validated first with a plastic tube filled with scattering liquid (milk) running at various controlled flow rates and then with the tube embedded under scattering layers (chicken breast) of varying thickness. The system includes a single, common camera, a commercial projector (profilometry channel), a laser light source (flow channel), and a computer station. In addition, orthogonal projection processing was combined with Hilbert transform, increasing the visualization and resolution of the measured flow profile.     

An experimental study and 1-D analysis of an ejector with a movable primary nozzle that operates with R236fa

The nozzle exit position is an important structural parameter of an ejector. Research shows that movable primary nozzle enhances performance of ejectors. The present work experimentally studied the critical entrainment ratios of an ejector at different nozzle positions, finding that the critical entrainment ratio first increases with the nozzle exit position and then remains constant. A 1-D model proposed to explain this phenomenon found that in a certain range, the critical entrainment ratio is determined by choking of the secondary flow in the converging cone. When the nozzle moves upstream, the mixed flow reaches sound speed at the constant area section, and the critical entrainment ratio remains unchanged.     

Shape optimisation of a two-phase ejector for CO2 refrigeration systems

The shape optimisation of four CO₂ ejectors is presented in this study. The considered ejectors were originally designed for a multi-ejector supermarket CO₂ refrigeration system. The objective function was formulated to consider the multiple operating regimes, where the goal of the optimisation was to maximise the device efficiency. Six geometrical parameters were considered in the optimisation procedure. The applied optimisation scheme was a combination of a genetic algorithm coupled with the effective and validated CFD tool, ejectorPL. The optimisation results showed that the ejector efficiency improved by 6%. The shape modification trends were similar for all of the considered ejectors. All of the shape modifications resulted in a smoother expansion inside the motive nozzle, less intense turbulence inside the mixing section and a more uniform velocity field inside the mixing section. The obtained results showed that the presented methodology can be effectively used for ejector design for numerous applications.     

Application of glyph-based techniques for multivariate engineering visualization

This article presents a review of glyph-based techniques for engineering visualization as well as practical application for the multivariate visualization process. Two glyph techniques, Chernoff faces and star glyphs, uncommonly used in engineering practice, are described, applied to the selected data set, run through the chosen optimization methods and user evaluated. As an example of how these techniques function, a set of data for the optimization of a heat exchanger with a microchannel coil is adopted for visualization. The results acquired by the chosen visualization techniques are related to the results of optimization carried out by the response surface method and compared with the results of user evaluation. Based on the data set from engineering research and practice, the advantages and disadvantages of these techniques for engineering visualization are identified and discussed.