Investigation on ejector design for CO₂ heat pump applications using Dymola

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Abstract

In this paper, the Dymola modelling tool is used to study the influence of ejector design onto the whole heat pump cycle working with carbon dioxide. The cycle is built using the components provided by the TIL Modelica library. It is found that the ejector models in TIL are quite limited, namely by their inability to properly capture the on-design plateau and rapid decrease in performance in off-design operation. Therefore, an in-house state-of-the-art ejector model, originally developed in Python, is implemented as a Dymola object. This model is then calibrated onto CO₂ experimental data. The operation of a simple CO₂ heat pump system is investigated, with focus on the ejector sizing at fixed geometry. It is found that there exists an ejector size that maximises the COP of the cycle. Furthermore, critical ejector pressure is not reached at this optimum COP point; the ejector is operating well under the on-design regime.

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About the authors

Antoine Metsue

Institute Mechanics, Materials, and Civil Engineering (iMMC), Université catholique de Louvain (UCLouvain)

Author for correspondence.
Email: antoine.metsue@usherbrooke.ca
Belgium, Louvain-la-Neuve

Yann Bartosiewicz

Institute Mechanics, Materials, and Civil Engineering (iMMC), Université catholique de Louvain (UCLouvain)

Email: yann.bartosiewicz@uclouvain.be
Belgium, Louvain-la-Neuve

Sébastien Poncet

Mechanical Engineering Department, Université de Sherbrooke

Email: sebastien.poncet@usherbrooke.ca
Canada, boulevard de l’Université, 2500, Sherbrooke

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Supplementary files

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2. Fig. 1. Comparison of the two ejectors models in TIL with the present model. Left: pp,0 = 95 bar; Right: pp,0 = 85 bar.

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3. Fig. 2. Schematic of the ejector model of Metsue et al. [9].

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4. Fig. 3. Fitting of the model onto the experimental data of Zhu et al. [14]. Blue: pp,0 = 8.7 bar; Red: pp,0 = 9.3 bar; Black: pp,0 = 9.8 bar.

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5. Fig. 4. Schematic of the heat pump cycle.

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6. Fig. 5. Ejector operating conditions and COP of the cycle as a function of the ejector size. The dashed line delimits on- and off-design regimes.

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