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

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

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

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

Long-term safety and efficacy of benralizumab in patients with severe, uncontrolled asthma: 1-year results from the BORA phase 3 extension trial

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