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Experimental study of a two-phase ejector for CO2 transcritical refrigeration system

Haberschill Philippe, Nehdi Ezzeddine, Kairouani Lakdar, Elakhdar Mouna Abouda

Archives of Thermodynamics

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2021

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Vol. 42, no 4

217--246

EN

The geometry and operating parameters have an important influence on the performance of ejectors. The improvement of the refrigeration cycle performance and the design of the ejectors for the compression energy recovery requires a detailed analysis of the internal ejector working characteristics and geometry. To this aim, an experimental investigation of an ejector refrigeration system is conducted to determine the effect of the most important ejector dimensions on ejector working characteristics and system performance. Different dimensions of ejector components are tested. The influence of the ejector’s geometrical parameters on the system performance was analysed. The experiments with respect to the variation of ejector geometry such as the motive nozzle throat diameter, the mixing chamber diameter and the distance between the motive nozzle and diffuser were carried out. There exist optimum design parameters in each test. The experimental results show that the performance (entrainment ratio and a compression ratio of the ejector) increases significantly with the position between the primary nozzle and the mixing chamber. A maximum entrainment ratio of 57.3% and a compression ratio of 1.26 were recorded for the different parameters studied. The results obtained are consistent with experimental results found in the literature.

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Study of capillary tube applications in a transcritical heat pump system

Królicki Z., Białko B.

Archives of Thermodynamics

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2006

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Vol. 27, no. 4

123-146

EN

Capillary tubes have been used in refrigeration systems for many years, but not with a transcritical CO[2] system. The effects of capillary tubes in a transcritical CO[2] refrigerating system have been investigated theoretically. This paper presents a non-adiabatic homogeneous model of carbon dioxide flow through a capillary tube, where the carbon dioxide undergoes a phase change from supercritical fluid flow to subcritical two-phase flow. The model is based on fundamental conservation equations of mass, momentum and energy. These equations are solved simultaneously through iterations. The in-tube flow can be divided into a single-phase region and a two-phase region. The extreme choked situation at the outlet is evaluated by local sonic velocity judgment. Relationships between gas cooler pressure, evaporating temperature, ambient heat transfer coefficient and other parameters are presented and analyzed in detail.

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Optimization of transcritical CO[2] thermodynamic cycle for cooling and heating applications

Białko B., Królicki Z., Zajączkowski B.

Archives of Thermodynamics

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2006

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Vol. 27, no. 4

23-34

EN

CO[2] is a potential substitute for synthesized refrigerants with favourable environmental properties. Improvment of the coefficient of performance (COP) of carbon dioxide refrigeration, heat pumping and heating - cooling systems is a necessary condition. Energetic and thermodynamic analysis as well as optimisation studies of an isentropic and nonisentropic compression process are presented in the article. The results show that COP of the transcritical carbon dioxide cycle varies with the heat rejection pressure. Maximum COP occurs at an optimal heat rejection pressure, which depends mainly on outlet temperature of the gas cooler, evaporation temperature and performance of compressor. Correlations of the optimal heat rejection pressure in terms of appropriate parameters were obtained for specific conditions based on simulations of the cycle. The COP changes indicate that such system is more suitable for high heating end temperatures and modest cold end temperatures. Expressions for optimum cycle parameters have been developed. These correlations offer useful guidelines for optimal system design and for selection of appropriate operating conditions.