Experimental Test Rig For The Visualisation Study Of The Transcritical Flow In The Two-Phase R744 Ejectors

Recent studies have provided the significant number of approaches to enhance the performance of a twophase ejector, especially for transcritical CO2 cycles. However, the investigation of the mixing process is still challenging matter due to the highspeed fluid flow coupled with mixing of vapour and partially evaporated liquid stream. On the other hand, these phenomena directly influence the ejector efficiency. The behaviour of the aforementioned processes would be valuable for validation the numerical models as well as a required control of the system operation. Hence, in this work, the laboratory test rig for visualisation of the CO2 ejector mixing processes along suction nozzle, premixing chamber and diffuser was developed and manufactured. The visualisation techniques used for this study include the highspeed camera recordings and PIV measurements. The work consists of installation description, including the measurement approaches, solution predicted by the computational model for the transparent construction of the ejector and visualisation procedures. The selected onand offdesign operating points were described having regard ejector performance factors and its correlation with the output of the visualisation procedure

The Efficient Computational Tools For The Design Process Of The Transcritical Two-Phase Ejectors For Natural-Based Working Fluids

Naturalbased working fluids for refrigeration are becoming a standard commercial solution due to the dynamic research and development in this area as well as law regulations. The stateoftheart ejector technology for R744 systems reached current status due to a significant interest on modelling approaches and effective regulation concepts. The development path of the fast and efficient design tools based on the numerical simulations could be described as a key feature for the R744 commercial technology. In this study, one of the most effective numerical approaches dedicated for the twophase CO2 ejector design and analysis is discussed. Namely, homogeneous equilibrium and relaxation model for high motive pressures and mixture approach for lower motive pressures were reviewed. According to the requirements of the effective design tools, the comparison also included a prediction of the vapour quality at given operating conditions and the corresponding computational costs. Moreover, several research studies on swirling and bypassing solutions as well as commercial applications of multiejector device and reduced order models for regulation systems where aforementioned models were used was described. Conclusions on a potential of the reviewed approaches were formulated having regard possible utilisation for the design process of the ejector based R744 systems

Development of the natural working fluid‐based refrigeration system for domestic scale freeze‐dryer

In this work, the analysis of the refrigeration system designed for the FrostX 10 freeze‐dryer is presented. The main goal of this study was to experimentally investigate the reference R452a freeze‐dryer and prepare recommendations for a machine based on the R290 refrigeration unit. In order to guarantee the temperature requirements and efficient operation of that unit, the analysis of suitable natural refrigerants was performed. Consequently, propane (R290) was selected. In addition, a number of modifications were introduced for the prototype system. System analysis showed that the replacement of the refrigerant in the existing system improves the system energy efficiency by approximately 18%. During the experimental campaign of the basic refrigeration unit, an unstable operation of the evaporator was found. The concept of a new cooling system for a prototype device was presented. The configuration and type of heat exchanger to maximise the performance of the ice trap of the freeze‐dryer were proposed.Development of the natural working fluid‐based refrigeration system for domestic scale freeze‐dryeracceptedVersio

Thermal analysis of 8.5 MVA disk-type power transformer cooled by biodegradable ester oil working in ONAN mode by using advanced EMAG–CFD–CFD coupling

Power transformers are the first devices used to transfer the electrical energy produced in power plants to the grid to supply the industrial and individual receivers with electricity. The heat generation in windings and core, being an effect of the power losses, is usually dissipated in large units by using mineral oils, which are harmful to the environment. Nowadays, the industry and global society seek environmentally-friendly alternatives. One of the most promising substitute for their high biodegradability, safety in operation, and favourable thermo-physical properties are natural ester oils. For this reason, a numerical study of 8.5 MVA disk-type power transformer cooled using conventional mineral oil and a commercially used rapeseed ester oil is presented in this paper. Moreover, due to different thermal behaviour of the considered oils, the comparison was made for the unit working in different seasons of hot and moderate climate zones (Argentina and Poland). In the numerical approach, electromagnetic (EMAG) and computational fluid dynamics (CFD) models were used for a detailed study of the selected device. In particular, a novel and very efficient EMAG–CFD–CFD coupling procedure was developed to assess the cooling of the large power transformer. Such a coupled computational procedure allowed for the detailed investigation of the power loss, oil flow characteristics, and temperatures with a satisfying computational effort. The results showed that the average windings temperatures are higher by 2–9 K when the ester oil is used, dependent on the ambient conditions. The hotspot temperature in the low voltage windings increased by up to 9 K and up to 18 K in the high voltage windings using ester oil. According to the results, the oil duct construction requires modification in the high voltage region for transformers cooled using mineral oil in cold climate conditions.Fil: Stebel, Michal. Silesian University Of Technology; PoloniaFil: Kubiczek, Krzysztof. Silesian University Of Technology; PoloniaFil: Rios Rodriguez, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; ArgentinaFil: Palacz, Michal. Silesian University Of Technology; PoloniaFil: Garelli, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; ArgentinaFil: Melka, Bartlomiej. Silesian University Of Technology; PoloniaFil: Haida, Michal. Silesian University Of Technology; PoloniaFil: Bodys, Jakub. Silesian University Of Technology; PoloniaFil: Nowak, Andrzej J.. Silesian University Of Technology; PoloniaFil: Lasek, Pawel. Silesian University Of Technology; PoloniaFil: Stepien, Mariusz. Silesian University Of Technology; PoloniaFil: Pessolani, Francisco. Tadeo Czerweny S.a.; ArgentinaFil: Amadei, Mauro. Tadeo Czerweny S.a.; ArgentinaFil: Granata, Daniel. Tadeo Czerweny S.a.; ArgentinaFil: Storti, Mario Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; ArgentinaFil: Smolka, Jacek. Silesian University Of Technology; Poloni

Design and simulations of Refrigerated Sea Water Chillers with CO2 ejector pumps for marine applications in hot climates

According to provided literature review, many investigations concerned improvement possibilities of carbon-dioxide refrigeration units. Basis for further development of this technology are located in environmentally friendly working fluid, law regulations and large possibilities of further performance improvement of these systems. Several applications including large units operating for cooling and heating purposes of supermarkets and food industry, transport industry as well as whole district heating systems were successfully implemented to the market. Thermodynamic character of carbon-dioxide required many performance improvement based on various system configurations and control strategies, especially in hot climates as Mediterranean. However, mentioned applications are characterised by no limits of available space for system equipment. Whereas, these limitations is one of the major challenges in the case of marine industry and fishing vessels. Matter of performance in higher temperatures of operation and limited space at fishing vessel was main challenges of the thesis. Meanwhile, conditions of higher ambient temperatures are related with higher power consumption for the same cooling capacity. Such a situation is mostly related with necessity of additional compressors unit. Proposal of system modification according to mentioned factors was stated as a main goal of the project. On the basis of measurement data delivered by Kuldeteknisk AS, mathematical model of baseline installation was developed. Several crucial factors as heat exchanger capacity, system power consumption and ejector operation had to be taken into consideration. Proposed alternative system layouts were analysed on the basis of roper sets of operating conditions characteristic for high ambient conditions. Series of simulations for various climate zones were performed in order to evaluate systems performance. Having regard that an additional compressor increases the space requirement, analysis of modifications in the light of limited space and reduction of power demand were performed. Obtained results allowed for performance comparison of baseline installation working at Norwegian coast with modified systems in warm climates. Finally, up to 70\% of performance improvement was obtained in the case of most advanced installation working in warm east-Asian waters. Provided results showed that proper design of the system should ensure no necessity of an additional compressor in warmer climates with maintaining of the same cooling capacity. Hence, the described system could be implemented to the other markets bringing ecological and advanced solutions suitable for more demanding operation conditions

Non-equilibrium approach for the simulation of CO2 expansion in two-phase ejector driven by subcritical motive pressure

A non-equilibrium approach was proposed for highly accurate modelling of the expansion process during two-phase flow in the convergent-divergent motive nozzle of an R744 ejector. Comprehensive mapping of the coefficients used in the source terms of the additional transport equation of the vapour quality was provided on the basis of four ejector geometries. The calibration range contained motive pressures from 50 bar to 70 bar, where the prediction quality of the homogeneous equilibrium (HEM) and relaxation (HRM) models, was unsatisfactory. The calibrated model was validated on the basis of experimental mass flow rate data collected from 150 operating points. The mapping results were utilised for final model derivation in the form of an approximation function for R744 expansion. The validation process resulted in satisfactory relative error below 10% for the vast majority of the cases. Moreover, 70% of the simulated cases were considered with a mass flow rate discrepancy below 7.5% in the inaccuracy. Finally, the selected cases were compared and discussed with the HEM approach on the basis of field results. © 2020 Elsevier Ltd and IIRacceptedVersio

Design and simulations of refrigerated sea water chillers with CO2 ejector pumps for marine applications in hot climates

Various system configurations have been developed to improve the R744 systems under hot ambient conditions. However, stationary land applications are characterised by negligible limits on space for system equipment, unlike the marine industry, i.e. on-board fishing vessels. The baseline CO2 refrigeration system for fishing vessels was developed by a cooperating industrial company, namely the Refrigerated Sea Water Chillers operation on the Norwegian coast, which confirmed the successful application of this approach. In this study, modified layouts are evaluated for operation in warmer climates without the need for an additional compressor unit, thus maintaining the compactness of the unit. Flash gas valve-, parallel compression- and multi-ejector systems were numerically investigated including ejectors section and flooded evaporator. Sea water temperatures as occurring in Mediterranean and East-Asian waters were investigated. Both the optimal high-pressure as well as the pressure level in an intermediate pressure receiver were controlled to achieve low energy consumptions. Finally, an up to 70% performance improvement was obtained in the case of the most advanced installation working in warm East-Asian waters. The obtained results showed that the proper design of the system should ensure no necessity for an additional compressor in warmer climates while still maintaining the designed cooling capacity.acceptedVersio

Parallel Work of CO2 Ejectors Installed in a Multi-Ejector Module of Refrigeration System

A performance analysis on of fixed ejectors installed in a multi-ejector module in a CO2 refrigeration system is presented in this study. The serial and the parallel work of four fixed-geometry units that compose the multi-ejector pack was carried out. The executed numerical simulations were performed with the use of validated Homogeneous Equilibrium Model (HEM). The computational tool ejectorPL for typical transcritical parameters at the motive nozzle were used in all the tests. A wide range of the operating conditions for supermarket applications in three different European climate zones were taken into consideration. The obtained results present the high and stable performance of all the ejectors in the multi-ejector pack. © Published under licence by IOP Publishing Ltd

Non-equilibrium approach in simulations of the R744 flow through the motive nozzle of the two-phase ejector

The ejector technology for R744 systems was continuously improved over the last two decades in the area of control and design processes. The latter should be related with a significant interest on modelling approaches including numerical simulations. However, some limitations of the existing approaches are still present, while the application range of the ejectors is still increasing regarding mobile and domestic applications. Namely, a quality of the flow prediction in the transcritical two-phase ejector varies depending on the operating conditions and correlated phenomena. The accurate and time efficient computational approach including the operating range of low condensing pressures is presented with the aim of more effective ejector design. The mixture approach developed on the basis of the Homogeneous Equilibrium Model is described regarding prediction of the motive and suction mass flow rate which are crucial for proper control procedures of the ejector-based refrigeration cycle. Additional equation for the vapour quality transport and re-formulated property definitions are utilised for proper control of the evaporation process in the motive nozzle of the ejector. Coefficients in source terms of the quality equation were mapped regarding high accuracy of the motive mass flow rate prediction. Hence, the calibration procedure of the coefficients, resulting in an approximation function as well as mapping of the suction nozzle accuracy regarding turbulence modelling and cavitation phenomena are introduced in this study. Finally, a comparison with the baseline homogeneous equilibrium model is given on the basis of the mass flow rate prediction and field parameters. Keywords: Carbon Dioxide, Transcritical Ejector, Phase change modelling, Expansion modellin

Design and simulations of refrigerated sea water chillers with CO2 ejector pumps for marine applications in hot climates

Various system configurations have been developed to improve the R744 systems under hot ambient conditions. However, stationary land applications are characterised by negligible limits on space for system equipment, unlike the marine industry, i.e. on-board fishing vessels. The baseline CO2 refrigeration system for fishing vessels was developed by a cooperating industrial company, namely the Refrigerated Sea Water Chillers operation on the Norwegian coast, which confirmed the successful application of this approach. In this study, modified layouts are evaluated for operation in warmer climates without the need for an additional compressor unit, thus maintaining the compactness of the unit. Flash gas valve-, parallel compression- and multi-ejector systems were numerically investigated including ejectors section and flooded evaporator. Sea water temperatures as occurring in Mediterranean and East-Asian waters were investigated. Both the optimal high-pressure as well as the pressure level in an intermediate pressure receiver were controlled to achieve low energy consumptions. Finally, an up to 70% performance improvement was obtained in the case of the most advanced installation working in warm East-Asian waters. The obtained results showed that the proper design of the system should ensure no necessity for an additional compressor in warmer climates while still maintaining the designed cooling capacity