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Stefan Elbel - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation into the influence of vortex control on transcritical r744 Ejector and cycle performance
Applied Thermal Engineering, 2020Co-Authors: Jingwei Zhu, Stefan ElbelAbstract:Abstract Vortex control over a diphasic convergent-divergent nozzle through adjustable nozzle inlet vortex can improve the performance of transcritical R744 Ejector cooling cycle due to its potential for flow control with less sacrifice of nozzle efficiency and no requirement of geometry change. In this study, the influence of vortex control on transcritical R744 Ejector and cycle performance has been experimentally investigated. Vortex control was applied to Ejectors with different geometric parameters. The results with vortex control were compared with those with series expansion valve control and needle control. Design guidelines for Ejector with vortex control were provided. It was found that the total work recovery efficiency of Ejector with vortex control can be better than series expansion valve control and is close to needle control. Vortex control can be used to improve system performance by adjusting the high-side pressure of the transcritical R744 Ejector cycle. Under off-design conditions, system capacity and COP can be improved by 11.0% and 8.1%, respectively, by applying vortex control.
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trade offs between design complexity and performance impacts for transcritical r744 Ejectors
8th Conference on Ammonia and CO2 Refrigeration Technology. Proceedings: Ohrid North Macedonia Avril 11-13 2019., 2019Co-Authors: Francesco Botticella, Stefan ElbelAbstract:It is well known that the transcritical CO2 cycle has higher intrinsic throttling losses than comparable subcritical cycles. Replacing the expansion valve with a two-phase Ejector greatly improves cycle performance by reducing throttling losses. However, Ejectors have yet to be successfully applied to low-capacity systems (approximately 1 to 5 kW), such as bottle coolers, window air conditioners, beverage dispensers, heat pump water heaters or similar. It is a real challenge to integrate Ejectors into mass produced systems of small capacity in a cost-effective manner due to the relatively complex design of an Ejector in comparison to simpler expansion devices. In addition to presenting system level results obtained with a transcritical CO2 bottle cooler with Ejector, another aim of this paper is to systematically determine the possibilities for cost reduction by identifying performance trade-offs of less complex Ejector designs. In a first step, a simplified diffuser design was investigated in combination with a conventional motive nozzle having converging-diverging design. Resulting system COPs and the impact on Ejector efficiency are reported.
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Review of recent developments in advanced Ejector technology
International Journal of Refrigeration-revue Internationale Du Froid, 2016Co-Authors: Stefan Elbel, Neal LawrenceAbstract:Abstract 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.
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experimental investigation of a two phase Ejector cycle suitable for use with low pressure refrigerants r134a and r1234yf
International Journal of Refrigeration-revue Internationale Du Froid, 2014Co-Authors: Neal Lawrence, Stefan ElbelAbstract:Abstract This paper presents the results of an experimental investigation in which the performance of the low-pressure fluids R134a and R1234yf was compared between a two-phase Ejector cycle and expansion valve cycles. An alternate two-phase Ejector cycle, in which the pressure lift provided by the Ejector was utilized in order to provide multiple evaporation temperatures, was constructed and tested. The experimental results show that Ejectors designed for low-pressure fluids were able to achieve similar but lower work recovery efficiencies compared to CO2 Ejectors. When compared to a two evaporation temperature expansion valve cycle, the Ejector cycle showed maximum COP improvements of 12% with R1234yf and 8% with R134a. When compared to a single evaporation temperature expansion valve cycle, the Ejector cycle showed maximum COP improvements of 6% with R1234yf and 5% with R134a. The effect of evaporator design on Ejector cycle COP improvement was also demonstrated experimentally.
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historical and present developments of Ejector refrigeration systems with emphasis on transcritical carbon dioxide air conditioning applications
International Journal of Refrigeration-revue Internationale Du Froid, 2011Co-Authors: Stefan ElbelAbstract:Abstract This paper gives an overview of historical and present developments on how Ejectors can be utilized to improve the performance of air-conditioning and refrigeration systems. Research on Ejector refrigeration cycles that utilize low-grade energy sources to produce cooling is summarized. Another major class of Ejector refrigeration cycles that is described tries to recover expansion work by means of a two-phase Ejector. This particular approach appears to be very promising for transcritical carbon dioxide (CO 2 , R744) systems with inherently large throttling losses. The paper further presents the latest analytical and experimental results of a comprehensive study carried out to investigate possible performance improvements of transcritical R744 two-phase Ejector systems. Relevant operational parameters were varied and effects on performance resulting from different Ejector geometries were studied as well. Two-phase mixing shock waves inside the Ejector were detected by recoding static wall pressure distributions.
Armin Hafner - One of the best experts on this subject based on the ideXlab platform.
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performance mapping of the r744 Ejectors for refrigeration and air conditioning supermarket application a hybrid reduced order model
Energy, 2018Co-Authors: Michal Haida, Jacek Smolka, Ziemowit Ostrowski, Michal Palacz, Kenneth Bank Madsen, Sven Forsterling, Andrzej J Nowak, Armin Hafner, Krzysztof BanasiakAbstract:Abstract The continuous derivation of the ambient temperature and cooling demand in CO2 refrigeration and air-conditioning systems equipped with multi-Ejector modules for supermarkets requires the analysis of the fixed Ejector utilisation in a very wide range of the operational envelope. Therefore, performance mapping of the four R744 Ejectors installed in the multi-Ejector pack was performed. The investigations of a single Ejector's work were performed based on the proposed hybrid reduced-order model to predict the performance of each Ejector under arbitrary operating conditions. The proposed model was validated and generated by use of the experimental data together with the computational fluid dynamic model results. The Ejector efficiency mapping indicated the area of the best Ejector performance in the range from approximately 50 bar–100 bar. The mass entrainment ratio of all four Ejectors was presented for different ambient temperatures and the pressure lift. An area of the mass entrainment ratio greater than 0.3 was obtained by each Ejector at ambient temperature above approximately 15 °C for pressure lift below 10 bar. The approximation functions of the Ejector pressure lift in terms of the ambient temperature for air-conditioning operating conditions to reach the best efficiency of each Ejector are proposed.
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full scale multi Ejector module for a carbon dioxide supermarket refrigeration system numerical study of performance evaluation
Energy Conversion and Management, 2017Co-Authors: Jakub Bodys, Michal Haida, Jacek Smolka, Michal Palacz, Andrzej J Nowak, Krzysztof Banasiak, Armin HafnerAbstract:Abstract The performance of fixed Ejectors installed in a multi-Ejector module in a carbon dioxide refrigeration system is discussed in this paper. To analyse the module operation, three-dimensional Ejector models including the inlet and outlet collecting ducts were considered. The tests were performed for three of four vapour Ejectors of different sizes that compose the multi-Ejector pack. The testing modes included the serial and parallel operation of the fixed units in operating conditions that are characteristic for the supermarket refrigeration unit working at high ambient temperatures. All numerical simulations were performed using the validated Homogeneous Equilibrium Model implemented on the EjectorPL computational tool for typical transcritical parameters at the motive nozzle port. The detailed analysis was executed separately for the Ejectors and the ducts of the module collectors. The results discussion concerned the crucial parameters for such an installation like the pressure and vapour quality distribution. Negligible influence of the motive nozzle collector and a crucial influence of the outlet collector shape was indicated. The global performance analysis showed that the multi-Ejector pack provides high and stable performance of all installed Ejectors over the entire range of the considered operating conditions for supermarket application. Areas of the possible pressure loss reduction and the uniformity growth in the vapour quality distribution were presented. Finally, according to the multi-Ejector pack ducts analysis, the potential areas for module shape optimisation were indicated as well.
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shape optimisation of a two phase Ejector for co2 refrigeration systems
International Journal of Refrigeration-revue Internationale Du Froid, 2017Co-Authors: Michal Palacz, Jacek Smolka, Andrzej J Nowak, Krzysztof Banasiak, Armin HafnerAbstract: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.
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performance of fixed geometry Ejectors with a swirl motion installed in a multi Ejector module of a co2 refrigeration system
Energy, 2016Co-Authors: Jakub Bodys, Michal Haida, Jacek Smolka, Michal Palacz, Andrzej J Nowak, Krzysztof Banasiak, Armin HafnerAbstract:This paper provides a performance comparison of fixed Ejectors with and without swirl flow at the inlet of the motive and suction nozzles installed in a CO2 supermarket refrigeration system. The Coefficient of Performance (COP) of the multi-Ejector-based refrigeration system is dependent on the design of this device. The literature suggests that one of the possible Ejector efficiency improvements can be performed using a swirl generator at the inlet of the motive nozzle. Therefore, a swirl generator was simulated for different size CO2 Ejectors under typical operating conditions in a supermarket and for a range of rotational speeds. To compare the potential of both solutions, the device performance was numerically simulated using a validated Homogeneous Equilibrium Model (HEM) model for the same transcritical parameters. A global efficiency was presented and discussed for both fixed Ejector types.
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performance comparison of fixed and controllable geometry Ejectors in a co2 refrigeration system
International Journal of Refrigeration-revue Internationale Du Froid, 2016Co-Authors: Jacek Smolka, Michal Palacz, Andrzej J Nowak, Jakub Bodys, Zbigniew Bulinski, Krzysztof Banasiak, Armin HafnerAbstract: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.
K Chunnanond - One of the best experts on this subject based on the ideXlab platform.
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performance prediction of steam Ejector using computational fluid dynamics part 2 flow structure of a steam Ejector influenced by operating pressures and geometries
International Journal of Thermal Sciences, 2007Co-Authors: Thanarath Sriveerakul, Satha Aphornratana, K ChunnanondAbstract:The aim of this study is to reveal the complication of the flow and the mixing process of a steam Ejector used in a jet refrigeration cycle by using the simulation software package (FLUENT). In Part 1 of this work, the CFD results of the steam Ejector's performance were validated with the experimental values. After the validation is satisfied, this paper is able to analyze the flow phenomena inside the steam Ejector when its operating conditions and geometries were varied. Using the applications provided by the CFD software, the flow structure of the modeled Ejectors could be created graphically, and the phenomena inside the flow passage were explored. The CFD method was evaluated as an efficient tool to represent the flow inside a steam Ejector.
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Ejectors applications in refrigeration technology
Renewable & Sustainable Energy Reviews, 2004Co-Authors: K Chunnanond, Satha AphornratanaAbstract:This paper provides a literature review on Ejectors and their applications in refrigeration. A number of studies are grouped and discussed in several topics, i.e. background and theory of Ejector and jet refrigeration cycle, performance characteristics, working fluid and improvement of jet refrigerator. Moreover, other applications of an Ejector in other types of refrigeration system are also described.
Satha Aphornratana - One of the best experts on this subject based on the ideXlab platform.
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comparison of traditional and crmc Ejector performance used in a steam Ejector refrigeration
Energy Procedia, 2017Co-Authors: Borirak Kitrattana, Tongchana Thongtip, Satha Aphornratana, Natthawut RuangtrakoonAbstract:Abstract In this paper, performance of a steam Ejector designed based on the constant rate of momentum change (CRMC) and traditional Ejector were tested in an attempt to compare its performance. Three different Ejectors were designed and constructed; traditional Ejector with throat diameter of 19 mm, traditional Ejector with throat diameter of 13.4 mm, and CRMC Ejector with throat diameter of 13.4 mm. They were designed to be easily equipped with the 1kW experimental Ejector refrigerator. The boiler saturation pressure was varied from 130°C to 140°. The evaporator saturation temperature were fixed at 7.5°C. The result show that at the same operating condition and the same Ejector area ratio (the area ratio of nozzle throat to Ejector throat), CRMC Ejector provided higher entrainment ratio than the traditional Ejectors while the critical condenser pressure remain the same.
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performance prediction of steam Ejector using computational fluid dynamics part 2 flow structure of a steam Ejector influenced by operating pressures and geometries
International Journal of Thermal Sciences, 2007Co-Authors: Thanarath Sriveerakul, Satha Aphornratana, K ChunnanondAbstract:The aim of this study is to reveal the complication of the flow and the mixing process of a steam Ejector used in a jet refrigeration cycle by using the simulation software package (FLUENT). In Part 1 of this work, the CFD results of the steam Ejector's performance were validated with the experimental values. After the validation is satisfied, this paper is able to analyze the flow phenomena inside the steam Ejector when its operating conditions and geometries were varied. Using the applications provided by the CFD software, the flow structure of the modeled Ejectors could be created graphically, and the phenomena inside the flow passage were explored. The CFD method was evaluated as an efficient tool to represent the flow inside a steam Ejector.
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Ejectors applications in refrigeration technology
Renewable & Sustainable Energy Reviews, 2004Co-Authors: K Chunnanond, Satha AphornratanaAbstract:This paper provides a literature review on Ejectors and their applications in refrigeration. A number of studies are grouped and discussed in several topics, i.e. background and theory of Ejector and jet refrigeration cycle, performance characteristics, working fluid and improvement of jet refrigerator. Moreover, other applications of an Ejector in other types of refrigeration system are also described.
Krzysztof Banasiak - One of the best experts on this subject based on the ideXlab platform.
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performance mapping of the r744 Ejectors for refrigeration and air conditioning supermarket application a hybrid reduced order model
Energy, 2018Co-Authors: Michal Haida, Jacek Smolka, Ziemowit Ostrowski, Michal Palacz, Kenneth Bank Madsen, Sven Forsterling, Andrzej J Nowak, Armin Hafner, Krzysztof BanasiakAbstract:Abstract The continuous derivation of the ambient temperature and cooling demand in CO2 refrigeration and air-conditioning systems equipped with multi-Ejector modules for supermarkets requires the analysis of the fixed Ejector utilisation in a very wide range of the operational envelope. Therefore, performance mapping of the four R744 Ejectors installed in the multi-Ejector pack was performed. The investigations of a single Ejector's work were performed based on the proposed hybrid reduced-order model to predict the performance of each Ejector under arbitrary operating conditions. The proposed model was validated and generated by use of the experimental data together with the computational fluid dynamic model results. The Ejector efficiency mapping indicated the area of the best Ejector performance in the range from approximately 50 bar–100 bar. The mass entrainment ratio of all four Ejectors was presented for different ambient temperatures and the pressure lift. An area of the mass entrainment ratio greater than 0.3 was obtained by each Ejector at ambient temperature above approximately 15 °C for pressure lift below 10 bar. The approximation functions of the Ejector pressure lift in terms of the ambient temperature for air-conditioning operating conditions to reach the best efficiency of each Ejector are proposed.
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full scale multi Ejector module for a carbon dioxide supermarket refrigeration system numerical study of performance evaluation
Energy Conversion and Management, 2017Co-Authors: Jakub Bodys, Michal Haida, Jacek Smolka, Michal Palacz, Andrzej J Nowak, Krzysztof Banasiak, Armin HafnerAbstract:Abstract The performance of fixed Ejectors installed in a multi-Ejector module in a carbon dioxide refrigeration system is discussed in this paper. To analyse the module operation, three-dimensional Ejector models including the inlet and outlet collecting ducts were considered. The tests were performed for three of four vapour Ejectors of different sizes that compose the multi-Ejector pack. The testing modes included the serial and parallel operation of the fixed units in operating conditions that are characteristic for the supermarket refrigeration unit working at high ambient temperatures. All numerical simulations were performed using the validated Homogeneous Equilibrium Model implemented on the EjectorPL computational tool for typical transcritical parameters at the motive nozzle port. The detailed analysis was executed separately for the Ejectors and the ducts of the module collectors. The results discussion concerned the crucial parameters for such an installation like the pressure and vapour quality distribution. Negligible influence of the motive nozzle collector and a crucial influence of the outlet collector shape was indicated. The global performance analysis showed that the multi-Ejector pack provides high and stable performance of all installed Ejectors over the entire range of the considered operating conditions for supermarket application. Areas of the possible pressure loss reduction and the uniformity growth in the vapour quality distribution were presented. Finally, according to the multi-Ejector pack ducts analysis, the potential areas for module shape optimisation were indicated as well.
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shape optimisation of a two phase Ejector for co2 refrigeration systems
International Journal of Refrigeration-revue Internationale Du Froid, 2017Co-Authors: Michal Palacz, Jacek Smolka, Andrzej J Nowak, Krzysztof Banasiak, Armin HafnerAbstract: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.
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performance of fixed geometry Ejectors with a swirl motion installed in a multi Ejector module of a co2 refrigeration system
Energy, 2016Co-Authors: Jakub Bodys, Michal Haida, Jacek Smolka, Michal Palacz, Andrzej J Nowak, Krzysztof Banasiak, Armin HafnerAbstract:This paper provides a performance comparison of fixed Ejectors with and without swirl flow at the inlet of the motive and suction nozzles installed in a CO2 supermarket refrigeration system. The Coefficient of Performance (COP) of the multi-Ejector-based refrigeration system is dependent on the design of this device. The literature suggests that one of the possible Ejector efficiency improvements can be performed using a swirl generator at the inlet of the motive nozzle. Therefore, a swirl generator was simulated for different size CO2 Ejectors under typical operating conditions in a supermarket and for a range of rotational speeds. To compare the potential of both solutions, the device performance was numerically simulated using a validated Homogeneous Equilibrium Model (HEM) model for the same transcritical parameters. A global efficiency was presented and discussed for both fixed Ejector types.
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performance comparison of fixed and controllable geometry Ejectors in a co2 refrigeration system
International Journal of Refrigeration-revue Internationale Du Froid, 2016Co-Authors: Jacek Smolka, Michal Palacz, Andrzej J Nowak, Jakub Bodys, Zbigniew Bulinski, Krzysztof Banasiak, Armin HafnerAbstract: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.