Ejector Component Research Articles

Experimental validation of the theoretical ejector model in a low-grade waste heat refrigeration system using R1233zdE as a working fluid

Rising electricity prices and environmental regulations make it increasingly economically justifiable to utilize low-temperature waste heat, generated as a by-product of many technological processes. One potential application is the conversion of heat into cooling capacity using an ejector refrigeration system, to replace conventional electric-consuming cooling systems. Such systems, despite numerous descriptions in the literature, have not found industrial applications up to date. This work presents experimental results on the first commercial prototype cooling system driven by 200 kW waste heat of ultra-low temperature between 60 °C and 70 °C coming from the oil system of air compressors operating under real industrial operating conditions. A refrigeration system configuration based on the use of heat recovery downstream of the ejector and splitting the waste heat recovery heat exchanger into two stages was applied. The low GWP and low-pressure HFO R1233zd(E) refrigerant was used as a working fluid. The high-temperature cooling parameters, equivalent to the glycol temperature of 16 °C/19 °C (outlet/inlet of the evaporator), were examined and the COP of 0,25 was obtained. To obtain such a promising COP value, the critical and subcritical parameters of the ejector were investigated. Based on the experimental results the validation of the ejector theoretical model was performed for low-pressure refrigerant. The ejector component characteristic efficiencies were optimized for the ejector calculation model, and ejector key performance parameters were estimated to a high accuracy. The average relative error in the estimation was 7.1%, 4.5%, and 13.7% for the mass entrainment ratio, pressure ratio and ejector total efficiency, respectively. The resulting accuracy is sufficient from the perspective of refrigeration system design.

Investigation on the influence of geometric parameters on two-phase ejector performance with R290

In this paper, the effect of geometric parameters on a two-phase ejector performance was experimentally studied, and the R290 was used as the working fluid. The four geometric parameters of the ejector were discussed in detail, including the diameter of the nozzle throat (Dt), the nozzle exit position (NXP), the diameter of the mixing section (Dm) and the length of the mixing section (Lm). The experimental results indicated that the pressure lift ratio (rp) of the ejector was sensitive to Dt and NXP. Within the increase of Dt and NXP discussed in this paper, the rp of the ejector varied from 1.13 to 1.33 and 1.32 to 1.07, respectively. In addition, a maximum rp of the ejector could be obtained when Dm was 3 mm to 4 mm under different nozzle throat diameter. When the Dt was 0.7 mm, the entrainment ratio of the ejector varied from 0.402 to 1.406 as the Dm varied from 2 mm to 6 mm. The Lm of the ejector diffuser had little effect on the ejector performance. Moreover, the empirical correlations for the efficiencies of R290 two-phase ejector components were summarized based on the experimental result and ejector model.

Investigation of improvement potential of a double-efficient CO2 cooling and heating system using an ejector with advanced exergy analysis

This paper presents an improvement potential investigation of a double-efficient CO2 cooling and heating system using an ejector, which can operate in cooling or heating mode. For the first time, advanced exergy analysis is employed to offer improvement direction and guidance for the practical application of this novel system. Compared to the conventional exergy analysis, which is widely used in previous work, advanced exergy analysis can supply more information about the interaction among components and the avoidable exergy destruction under the technical constrains. Thus, more practical and accurate conclusions can be drawn. The results reveal that 74.56 % of the total exergy destruction is endogenous in cooling mode, demonstrating the weak interaction among components. The compressor should be given the highest priority for improvement, due to its largest sum of avoidable exergy destruction (17.71 W). The effect of ejector component efficiency is also discussed. As it varies from 0.5 to 0.9, the system exergy efficiency rises from 11.59 % to 14.18 %. Furthermore, the proposed system shows great advantage with 31.31 % less exergy destruction compared to ejector expansion refrigeration cycle. In heating mode, the compressor also deserves to be optimized first. But the expansion valve possesses no effort for improvement due to its negative sum of avoidable exergy destruction (−1.203 W).

Experimental Assessment of the Efficiency of Two-Phase Ejector Components for Isobutane

Two-phase ejectors as well as single phase ejectors can be applied in many branches of industry: refrigeration and heat pump systems, chemical engineering, food processing, and others. Due to the complicated nature of the process of momentum transfer in two-phase ejectors, their design procedure based on the accurate theoretical prediction of the ejector performance is still an open issue. The paper provides its own experimental results of the velocity coefficients of the components of the two-phase ejector, i.e., the motive nozzle, suction chamber, mixing chamber, and diffuser. The results were obtained in the case of isobutane as the working fluid. It was demonstrated that the velocity coefficients may not be treated as constant quantities. Therefore, our own proposed dimensionless relationships describe the velocity coefficients of the components of the ejector that may be applied in the design procedure of the ejector. The two physical parameters, the wet vapour quality and the volumetric entrainment ratio, were selected as the key parameters. In addition, the aspects of the prediction of the critical mass flow rate of the motive nozzles was considered on the basis of the Henry–Fauske model. It was demonstrated that the model accurately predicts the two-phase critical flow under the conditions of a higher range of wet vapour quality.

Energy and exergy simulation analysis and comparative study of solar ejector cooling system using TRNSYS for two climates of Iran

This paper addresses hourly simulation of 3.5 kW Solar Ejector Cooling System (SECS) using R600a and R290 hydrocarbon refrigerants for application in two office buildings in semi-arid and hot-humid climates of Iran. During the period of the study, thermodynamics energy and exergy of the cooling systems when charged with the two refrigerants are fully assessed by simulation at the two study sites. The simulation studies of the entire cooling system indicate that the most irreversible process and hence the prime exergy destruction is related to the solar collector system followed by the ejector component in the cooling cycle. The ejector is a constant-area mixing (CAM) type which is mathematically modeled in Engineering Equation Solver (EES) software. Generator of the cooling cycle is modeled in EES using ε−NTU method and a simulation program is developed on TRNSYS-EES co-simulator for dynamic study of the cooling cycle. For comparison of efficiency of the two refrigerants, working conditions are set to be the same. The systems are equipped with auxiliary heaters to provide constant inlet temperature of 85C∘ for the generator when solar radiation is partially in phase with the building sites. The hourly and monthly simulation of both SECS in June, July, August and September 2019 demonstrate that R290 is more efficient for increasing the overall COP(=0.2844) of the system than R600a (COP=0.2797) of the building office in the semi-arid region where the generator receives most of its thermal energy from solar radiation in July 17, 2019. Although, the same refrigerant is also more efficient than R600a in the hot-humid region system in the same day, but the system compensates shortage of its necessary solar thermal energy mostly from the auxiliary heater.

Energy and advanced exergy analyses of novel ejector-compressor partially coupled refrigeration cycle for buildings with less solar energy

Solar-driven ejection–compression refrigeration is helpful for building space cooling but is based on the precondition of solar heat being infinite and free. This is not valid in many cases, such as multistorey buildings in metropolises with limited space. Even worse, in the carbon-neutral future, space surrounding buildings will be occupied by PV (photovoltaic) panels in priority. Therefore, a potential ejector-partially coupled enhanced compression refrigeration cycle consuming less heat is presented. Models of the new cycle for a multistorey building are established. Then, energy comparison and advanced exergy analysis are conducted. The analysis results first show that the new cycle needs no auxiliary system. Powered by limited low-grade heat, its COPe increased by 20.66% and total annual cost reduced by 7.8%, compared with the traditional ejector–compressor cycle. Advanced exergy analysis also finds that the order of improvement potential is compressor (4739.45 W), evaporator (4329.85 W), and condenser (2843.51 W), according to the sum of avoidable exergy destruction. This is different from the results of conventional exergy analysis. The sensitivity analysis of the ejector components' efficiencies is investigated, which has seldom been reported for refrigeration system with ejector. The results reveal that once the efficiencies of ejector components reach a certain point (0.94), the performance no longer improves. Generally, this work provides a potential ejection–compression cycle, demonstrates system improvement direction through advanced exergy analysis, and reveals good understanding of the system.

Advanced exergy analysis of a CO2 two-phase ejector

Ejector is meaningful and valuable to improve the transcritical CO2 refrigeration system. To study in-depth on the exergy destruction is significant for the performance enhancement of CO2 ejector. This paper presents a comprehensive investigation on the exergetic performance of CO2 two-phase ejector using conventional and advanced exergy analysis method to explore the interactions among ejector components and their improvement potential. The effects of primary flow pressure, suction flow temperature and area ratio (motive nozzle throat area to mixing chamber area) on the ejector exergy destruction are discussed. The results indicate the largest exergy destruction in the ejector is caused by the mixing chamber, followed by the motive nozzle, diffuser and suction chamber. Based on the avoidable exergy destruction rate and exergy destruction proportion, the order of optimization potential for ejector components is motive nozzle, diffuser, mixing chamber and suction chamber. However, the sum of avoidable exergy destruction of mixing chamber is the largest, which has the highest priority for improvement of overall ejector performance. The exogenous exergy destructions of the mixing chamber and diffuser are largely caused by the motive nozzle, and the exergy destructions would be increased with the improvement of motive nozzle performance. There exists an optimal primary flow pressure 9.5 MPa to minimize the exergy destruction of the each component of the ejector. To reduce the suction flow temperature and the ejector area ratio can decrease the avoidable exergy destruction of the components. Moreover, the variation of operating parameter has no effect on the optimization sequence of the overall ejector and its components. This work would provide a helpful way to guide the optimization on the ejector efficiency.

An improved 1-D thermodynamic modeling of small two-phase ejector for performance prediction and design

• An improved 1-D thermodynamic modeling of small two-phase ejector is presented. • The performances of the presented modeling are predicted. • The effects of the operating conditions and geometry parameters are analyzed. • The research results can provide theoretical direction about the ejector design. In this paper, an improved thermodynamic model for the design of a small two-phase ejector is proposed by using the constant-pressure mixing modeling method. Particularly, the mixing process modeling is associated with the area variation of the mixing section, where a corresponding area ratio of the mixing section entrance to exit is introduced. Meanwhile, the mixing pressure is determined by solving model equations under given operating conditions. Furthermore, the effects of the mixing area ratio, operating conditions, ejector components efficiencies on the ejector performance and geometry parameters are analyzed by the proposed model. The results show that the entrainment ratios increase from 0.47 to 1.14 as mixing area ratios range from 1.0 to 1.2 under the given conditions. The mixing area ratio has significant influences on the ejector performance at lower pressure lift ratio, higher primary fluid temperature and lower secondary fluid temperature. It can be concluded that the entrainment ratio, mixing pressure and mixing velocity of ejector could be improved with the mixing area ratio increasing. And it is further confirmed that the constant-pressure mixing ejector provides better performance than the constant-area mixing ejector under design operating conditions. The research results can provide theoretical guidance about the ejector design and performance predictions.

R744 ejector simulation based on homogeneous equilibrium model and its application in trans-critical refrigeration system

The operational efficiency of the trans-critical R744 refrigeration system was analyzed from the perspectives of both the refrigeration system and the ejector components based on the refrigeration system thermodynamic and the ejector models. Considering the basic principle of the ejector and the homogeneous equilibrium model (HEM), the computational fluid dynamics software FLUENT was adopted to perform CFD simulations on the design of the R744 two-phase flow ejector. Further, the operational efficiency of a trans-critical R744 refrigeration system was analyzed from the perspectives of both the refrigeration system and the ejector components employing the refrigeration system thermodynamic and the ejector models. It was found that in the trans-critical mode, the power consumption of the R744 parallel compression trans-critical refrigeration system (EPR) with an ejector was always lower than that of the traditional R744 parallel compression trans-critical refrigeration system (BPR), and the maximum power consumption was reduced by 22.8%.

Performance analysis of a water ejector using Computational Fluid Dynamics (CFD) simulations and mathematical modeling

A quasi-one-dimensional (1D) mathematical model coupled with Computational Fluid Dynamics (CFD) simulations of a water ejector is presented. Using data from CFD simulations, the mathematical model was used to calculate the friction loss coefficients of the ejector components, to predict its maximum efficiency point and to delimit its envelope of operation. The CFD approach was validated with experimental data and employed the finite element method to test the main turbulence models found in the literature (k-ε, k-ω and k-ω SST) for incompressible-flow ejectors. A set of operational conditions (OP) was tested and results show that the k-ω SST turbulence model is the most suitable to capture the ejector flow characteristics in all OP. In addition, for higher entrainment ratio (M) values, it was observed a possible correlation between how well the boundary layer can be solved and how the model is able to capture the ejector efficiency curve. Moreover, for lower M values, another possible correlation may be stated between how the turbulence model is able to capture the velocity profile.

Computational fluid-dynamics modelling of supersonic ejectors: Screening of modelling approaches, comprehensive validation and assessment of ejector component efficiencies

The efficiency of ejector-based systems (the “system-scale”) relies on the behaviour of the ejector (the “component-scale”), related to the flow phenomena within the component itself (the “local-scale”). As a consequence of this multi-scale connection, the precise prediction of the “local-scale” is of fundamental importance to sustain the design of commercially viable ejector-based systems. Although it is widely accepted that computational fluid-dynamics can achieve the prediction of the “local-scale” (CFD) modelling approaches, a broad agreement regarding the performances of numerical methods is not reached: different authors applied different methods, and a complete validation is missing so far. This paper contributes to the current discussion and closes the knowledge gap by assessing the performances of a CFD approach for single-phase supersonic ejectors. To this end, a comprehensive validation has been conducted, encompassing a wide range of ejector designs, boundary conditions and working fluids; besides, a screening of modelling approaches is conducted, encompassing a wide range of mesh criteria, geometrical modelling (2-Dimensional and 3-Dimensional approaches), solvers (density-based and pressure-based) and turbulence models (k-ε RNG and k-ω SST). The extensive comparison with experimental data allowed assessing and determining the influence of mesh criteria, geometrical modelling, solvers and turbulence models. In particular, k-ω SST has shown the best agreement with the experimental measurements concerning both global and local flow quantities, with an average entrainment ratio error of 14% and a maximum of 20%, under on-design operating mode. Finally, the simulation outcomes have been further post-processed to derive ejector component efficiencies, to contribute to the present discussion regarding closures in lumped parameter ejector modelling approaches. In conclusion, 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.

Performance evaluation of a modified R290 dual-evaporator refrigeration cycle using two-phase ejector as expansion device

This paper presents a modified dual-evaporator ejector expansion refrigeration cycle (MDEEC) in which a two-phase ejector is used as the expansion device to recover the expansion work. Based on constant-pressure mixing theory, a thermodynamic model is developed to investigate the effects of various parameters on the system performance. Also a comparative study of the modified cycle with a conventional one (CDVCC) and a previous ejector cycle (COSEC) is conducted in terms of energy and exergy analysis. The results show that COP of the modified cycle is improved by about 10% and the exergy destruction of expansion device is reduced by more than 90% compared with the COSEC. At the operating condition of Tc = 45 °C and Te2 = 5 °C, the COP and exergy efficiency of the MDEEC can reach 6.515 and 0.3184, respectively, which are 42.6% and 36.7% higher than those of the CDVCC. It is also revealed the performance improvements become more significant at higher condensing temperatures or lower evaporating temperatures. Finally, the effects of the ejector components efficiency and the performance under off-design conditions are discussed.

Numerical optimization of a novel gas-gas ejector for fuelling of hydrogen vehicles

This paper focuses on the potential replacement of expansion valves in the fuelling process of hydrogen vehicle by use of ejectors. The main advantage of the ejectors is to exploit the kinetic energy of a high-pressure primary flow to entrain a lower pressure secondary flow resulting in an improved and efficient fuelling process.First, a one-dimensional thermodynamic model was developed to characterise the ejector's performances such as its entrainment ratio and compression ratio. Then, the ejector's components efficiencies of the one-dimensional model were extracted from CFD simulations with the use of a genetic algorithm. Three regression models were compared to express the efficiencies as a function of the boundary conditions (pressure inlets) and the ejector's geometry (aspect ratio). Finally, the one-dimensional model was used to optimize the performance of the ejector for fuelling of hydrogen vehicles by using a simple transient simulation model of the vehicle tank. The new ejector fuelling procedure was compared with the traditional use of expansion valves. The results show that a reduction of the high-pressure hydrogen demand is possible using the optimized ejector, leading to reduced energy consumption, as well as fuelling time.

A performance evaluation of the ejector refrigeration system based on thermo-economic criteria through multi-objective approach

This work investigates an exhaust heat-driven ejector refrigeration system with the thermo-economic considerations. The system is thermally modelled and is optimized considering the performance coefficient and the total annual cost as two objectives using heat transfer search algorithm. Generator temperature, evaporator temperature and condenser temperature are considered as design variables. A 2-D shock circle model is used to simulate the ejector component with R245fa refrigerant. The results of multi-objective optimization are discussed using the Pareto frontier obtained between both conflicting objective functions. The effect of varying the nozzle throat diameter and the ecological function on the thermo-economic objectives is presented and discussed. The sensitivity analysis of the objective functions to the decision variables is investigated. Further, the exergo-economic results at the optimal point are also presented and discussed. The results reveal that the ejector and the generator are the leading contributors to the exergy destruction and hence to the total annual cost. The coefficient of performance and total annual cost at the best optimal point are 0.3 and 25,903 $/year, respectively. The optimized product unit cost of the system is 53.8 $/GJ with 10.5% exergy efficiency.

Effects of component geometries and inflow conditions on ejector operational mode

The ejector system is a useful device for creating high altitude conditions for ground tests of supersonic engines. The ejector performance can be immediately changed by varying the ejector operational mode. The ejector nozzle pressure ratio is well known to have a significant effect of the operational mode of an ejector. However, the effects of the mixing duct length and other geometric design parameters on the ejector mode change have not been clearly determined. In this study, the effects of ejector component geometries and inflow conditions on ejector operational mode are investigated by numerical analysis. By changing the inflow conditions and geometric parameters, twelve test cases are studied. Using the numerical test results, the flow pattern and suction pressure performance of the ejector with a fixed secondary mass flow rate are compared. In the numerical test results, a high primary nozzle stagnation pressure induces a highly underexpanded flow, resulting in the critical operational mode. For the critical operational mode, the mixing duct must be sufficiently long to accommodate the shock train and the choking zone. Primary nozzles with wide angles also induce widely expanded nozzle flows and result in the critical operational mode.

Investigation of the Liquid–Vapor Separator Efficiency on the Performance of the Ejector Used as an Expansion Device in the Vapor-Compression Refrigeration Cycle

Abstract Ejector expansion refrigeration cycle with reference to the constant pressure mixing theory is investigated to display the effects of the liquid–vapor separator efficiency on the performance, entrainment ratio, and area ratio at various operation conditions. Reversible ejector assumption is used for the highest theoretical performance limit, whereas efficiency of the liquid–vapor separator and all ejector components is added to the model to calculate more realistic performance improvement potentials. R1234yf and R1234ze(E) having low global warming potential values are used in the analyses. Zero-dimensional thermodynamic models are constructed applying the conservation equations between the inlets and outlets of the refrigeration cycle and ejector components. Percentage performance decrease is higher when the mixing section and the separator efficiency is added to the model at higher condenser temperatures compared with the lower evaporator temperatures according to the investigated operation ranges. Vapor and liquid separation efficiency affects not only the performance but also the design of the ejector although it is an external component since it has influence on the area ratio and entrainment ratio. Finally, the difference between the percentage performance improvement of the reversible ejector cycle and the realistic ejector cycle including the separator and ejector components efficiencies is as high as 35% at the highest investigated condenser temperature for R1234yf.

Thermodynamic Analysis of a Modified Ejector-Expansion Refrigeration Cycle with Hot Vapor Bypass

In this study, a modified ejector-expansion refrigeration cycle (MERC) is proposed for applications in small refrigeration units. A vapor bypass circuit is introduced into the standard ejector expansion refrigeration cycle (ERC) for increasing the ejector pressure lift ratio, thereby lowering the compressor pressure ratio in the MERC. A mathematical model has been established to evaluate the performances of MERC. Analysis results indicate that since a two phase vapor-liquid stream is used to drive the ejector in the MERC, a larger ejector pressure lift ratio can be achieved. Thus, the compressor pressure ratio decreases by 21.1% and the discharge temperature reduces from 93.6°C to 82.1°C at the evaporating temperature of -55°C when the vapor quality of two phase vapor-liquid stream increases from 0 to 0.2. In addition, the results show that the higher ejector component efficiencies are effective to reduce the compressor pressure ratio and the discharge temperature. Actually, the discharge temperature reduces from 91.4°C to 82.1°C with the ejector component efficiencies increasing from 0.75 to 0.85 at the two phase stream vapor quality of 0.2. Overall, the proposed cycle is found to be feasible in lower evaporating temperature cases.

1-D model for finding geometry of a single phase ejector

This paper presents a novel 1-D mathematical model to determine complete dimensions of an ejector component of Ejector Refrigeration System (ERS). The concepts of Prandtl's mixing length, Prandtl-Meyer expansion wave, Kelvin-Helmholtz instability and Baroclinic effect are introduced in the model to precisely determine the various diameters, mixing length, nozzle exit position etc. for the given conditions of the primary & secondary fluid, cooling capacity and critical condenser pressure. The area ratios obtained using the mathematical model are compared with the experimental/numerical results available in open literature for the same operating conditions and are found to be in good agreement. Moreover, ejector geometry determined from the proposed model is analyzed using CFD for the same input conditions. Average deviation in the entrainment ratio obtained using CFD and that given to the model is found to be less than 2.48% and thus model is validated again. The experimental test rig of ejector refrigeration system is also fabricated and the performance is evaluated while operating at critical condenser pressure. The deviation in the ejector geometry used in the experiment is found to be less than 7% in comparison to the ejector dimensions calculated by the numerical model for the same input conditions.

Evaluating performances of 1-D models to predict variable area supersonic gas ejector performances

The application of supersonic gas ejector with variable area nozzle can be found in different industries. However, due to different types of variable area nozzle, performance prediction is mainly focused on costly numerical simulations. In this paper, one-dimensional models for performance prediction of variable area gas ejector with specially designed nozzle, were compared. Additionally, operational lines and corresponding modes were analyzed. Two different variable area ejectors were experimentally tested. The first ejector used natural gas as motive fluid, whereas in the second one motive gas was the composition of alkane. Six distinct correlations of ejector component efficiencies were evaluated. Sum of absolute relative errors and coefficient of determination were used as goodness of fit criteria. The results showed that best model has coefficient of determination 0.76 and 0.63 in the case of natural and R2 gas as motive fluids, respectively. In order to improve prediction performances of entrainment ratio, the mixture of experts machine learning technique was used. Moreover, the results of obtained conditional probabilities of models are visualized in space spanned by area and pressure ratios. The presented analysis showed that one model is not generally better than others and can be improved by using an ensemble of models.

Assessment and prediction of component efficiencies in supersonic ejector with friction losses

In this paper, the influences of friction losses on ejector efficiencies are investigated by the computational fluid dynamics (CFD) technique. Roughness values factor is introduced to analyze ejector performance by considering the components efficiencies. Efficiencies of each component are assessed with different levels of roughness. Validation is given through comparisons between the calculated and experimental values obtained from the ejector refrigerant platform with diverse levels of surface roughness. Results indicate that the efficiency of the ejector decreases with the increase of roughness values and friction losses in constant-area section and diffuser have the most significant impact on ejector performance. By analyzing the relationship between efficiencies and roughness values, an efficiency correlation is built with a coefficient of determination over 0.9654. It is shown that proposed correlations for ejector component efficiencies can be utilized more accurately in system design of ejector based refrigerant system considering the friction losses.