Shape optimisation of a two-phase ejector for CO 2 refrigeration systems

Palacz, Michał; Smołka, Jacek; Nowak, Andrzej J.; Banasiak, Krzysztof; Hafner, Armin

doi:10.1016/j.ijrefrig.2016.10.013

Cited by 69 publications

(26 citation statements)

References 30 publications

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“…HEM considers liquid and vapor phases are in a homogeneous equilibrium whereas HRM uses the empirical correlation of the relaxation time. Lucas et al [89] and Palacz et al [90] employed HEM to predict the two-phase flow inside an ejector. The HEM accuracy decreases with a decline in a motive nozzle temperature and increases in deviation from the saturation line, which demands a more complex HRM mode.…”

Section: Expansion Devicementioning

confidence: 99%

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%

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

et al. 2019

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“…However, until relevant data based on the experimental tests focused on the local flow field visualisation will be available such a verification process is not possible. Nevertheless, the employed approach of the turbulence modelling was successfully validated in the study of R744 ejector optimisation (Palacz et al 2017) and multi-ejector block simulations (Bodys et al 2017). For this reason, the realisable k-ε model was utilised in this study as well.…”

Section: Mathematical Modelmentioning

confidence: 99%

“…According to the substantial developments of R744 ejectors, one of the most advanced numerical analysis investigations was delivered by (Palacz et al 2017), where full optimisation of ejector geometrical parameters was provided. A validated computational tool was used to simulate a transonic two-phase flow of the carbon dioxide trough ejector characteristic of the high pressure supermarket conditions (Palacz et al 2015;Smolka et al 2013).…”

Section: Introductionmentioning

confidence: 99%

“…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). The results noted a very sensitive function of the ejector efficiency relative to a needle position.…”

Section: Introductionmentioning

confidence: 99%

“…The regulation methods mentioned provide the possibility of the load regulation. Nevertheless, as described in (Banasiak et al 2014;Liu et al 2012;Nakagawa et al 2011;Nakagawa et al 2009;Palacz et al 2017;Smolka et al 2013Smolka et al , 2016, the high sensitivity of ejectors to operating conditions and designed geometrical parameters forces these devices to work with an optimal efficiency that is close to on-design operating conditions. Moreover, the optimal efficiency could be obtained only with a specified mass entrainment ratio and a corresponding pressure lift.…”

Section: Introductionmentioning

confidence: 99%

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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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