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

Smołka, Jacek; Palacz, Michał; Bodys, Jakub; Banasiak, Krzysztof; Fic, A.; Buliński, Zbigniew; Nowak, Andrzej J.; Hafner, Armin

doi:10.1016/j.ijrefrig.2016.01.025

Cited by 55 publications

(20 citation statements)

References 19 publications

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“…Figure 4 shows the variation in ejector efficiency with swirl RPM. In addition, the adjustable ejector configuration was found to enhance the system COP up to 30% compared to the fix-geometry ejector [97]. This was attributed to the fact that the adjustable ejector can provide a flexible control over the mass flow rate, which is the key to performance improvement.…”

Section: Expansion Devicementioning

confidence: 99%

“…For the later one, the nozzle throat area varies with the compressor speed and CO 2 mass flow rate, so that a correlation for the optimum nozzle throat area can be derived for a gas cooler pressure based on the dynamic system response. In addition, the adjustable ejector configuration was found to enhance the system COP up to 30% compared to the fix-geometry ejector [97]. This was attributed to the fact that the adjustable ejector can provide a flexible control over the mass flow rate, which is the key to performance improvement.…”

Section: Expansion Devicementioning

confidence: 99%

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Recent Advances in Transcritical CO2 (R744) Heat Pump System: A Review

et al. 2019

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Heat pump (HP) is one of the most energy efficient tools for address heating and possibly cooling needs in buildings. Growing environmental concerns over conventional HP refrigerants, chlorofluorocarbons (CFCs), and hydrofluorocarbons (HFCs) have forced legislators and researchers to look for alternatives. As such, carbon dioxide (R744/CO2) has come to light due to its low global warming potential (GWP) and zero ozone depleting characteristics. Even though CO2 is environmentally benign, the performance of CO2 HP has been of concern since its inception. To improve the performance of CO2 HP, research has been playing a pivotal role in developing functional designs of heat exchangers, expansion devices, and compressors to suit the CO2 transcritical cycle. Different CO2 HP cycles coupled with auxiliary components, hybrid systems, and refrigerant mixtures along with advanced control strategies have been applied and tested. This paper presents a complete overview of the most recent developments of transcritical CO2 HPs, their components, and applications.

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Section: Expansion Devicementioning

confidence: 99%

Section: Expansion Devicementioning

confidence: 99%

Recent Advances in Transcritical CO2 (R744) Heat Pump System: A Review

et al. 2019

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“…Studies on implementation of the ejectors with converging-diverging nozzles in refrigeration, airconditioning and heat pumps demonstrated significant improvement of the energy efficiency of the discussed systems [1][2][3]. As a result, a growing interest in studying an operation and design of the ejector in mentioned systems can be observed [4][5][6]. The accurate prediction of a critical mass flow rate of the flow through the ejector motive nozzle is crucial for an appropriate design of the ejector [7].…”

Section: Introductionmentioning

confidence: 99%

Application of a fast transonic trajectory determination approach in 1-D modelling of steady-state two-phase carbon dioxide flow

2019

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An original generalised procedure of determination of the transonic trajectory has been proposed. The procedure is much faster than the commonly used Newton Critical Point approach. The approach was applied in modelling of a carbon dioxide transonic two-phase flow through the converging-diverging nozzle by means of the Homogeneous Equilibrium Model and Delayed Equilibrium Model (DEM). The simulations concern flows that were experimentally and theoretically investigated in the literature. DEM was prev ously used only in choked water flow simulations. Its application in CO2 flow modelling and the supersonic trajectory part determination is a novel contribution. The adjusted for CO2 version of the closurelaw was proposed. The investigation revealed that the applied Darcy friction factor determination approach has a significant influence on the results. Moreover, the models are unable of producing physically acceptable solutions until theLockhartMartinelli approach is utilised. It was shown that the Friedel approach might be considered more proper for CO2 flows.

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“…Nevertheless, in this study, an air conditioning cycle was used for the experimental tests with a relatively low compressor power of approximately 10 kW. Evaluation of a controllable ejector performance for various loads characteristic of large refrigeration units such as in supermarkets was presented by (Smolka et al 2016). A full numerical comparison of a controllable and fixed geometric efficiency was based on the same baseline models characterised by high efficiency as in the work of (Palacz et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Performance improvement of the R744 two-phase ejector with an implemented suction nozzle bypass

Bodys

Smołka

Banasiak

et al. 2018

International Journal of Refrigeration

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In this study, the concept of an R744 ejector with a bypass duct of a suction nozzle was presented. The design of the geometry and bypass positioning in a mixing section, and the idea of regulation, as well as integration, with a suction nozzle duct was described. A preliminary numerical analysis of the proposed bypass geometry was also presented. The computational platform ejectorPL integrated with an extensively validated mathematical model of transcritical R744 two-phase flow was used. Motive nozzle inlet and suction nozzle inlet conditions reflecting gas cooler and evaporator conditions characteristic of large systems, such as supermarket refrigeration units, were examined. Three different separation pressures in liquid receivers were assumed for two bypass geometries and six bypass inlet positions. The bypass positioning as a function of a mixer length was presented. Uniquely positive results were obtained for the lowest pressure conditions. Namely, the increment of the suction mass flow rate was substantial and equal to 36.9% for the bypass angle of 19°. Hence, the bypass implementation resulted in distinct potential of an efficiency improvement-from 22.2% to 30.4%. A higher pressure lift case did not result in any improvement of the ejector work. The influence of the bypass geometry on the overall ejector efficiency was preliminarily characterised. Finally, the pressure distribution in the bypass type ejector was described.

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

Cited by 55 publications

References 19 publications

Recent Advances in Transcritical CO2 (R744) Heat Pump System: A Review

Recent Advances in Transcritical CO2 (R744) Heat Pump System: A Review

Application of a fast transonic trajectory determination approach in 1-D modelling of steady-state two-phase carbon dioxide flow

Performance improvement of the R744 two-phase ejector with an implemented suction nozzle bypass

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