Conference article

Investigation of Energy Dissipation in an Ejector Refrigeration Cycle

Christian Tischendorf
Technical University Braunschweig, Department of Thermodynamics, Germany

Denise Janotte
TLK Thermo GmbH, Germany

Ricardo Fiorenzano
Technical University Braunschweig, Department of Thermodynamics, Germany

Wilhelm Tegethoff
TLK Thermo GmbH, Germany

Download articlehttp://dx.doi.org/10.3384/ecp09430090

Published in: Proceedings of the 7th International Modelica Conference; Como; Italy; 20-22 September 2009

Linköping Electronic Conference Proceedings 43:33, s. 304-311

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Published: 2009-12-29

ISBN: 978-91-7393-513-5

ISSN: 1650-3686 (print), 1650-3740 (online)

Abstract

The presented work focuses on the differences in energy dissipation in each cycle component compared to the energy dissipation of the whole ejector refrigeration cycle. With help of this analysis; improvement of energetic efficiency by using an ejector can be set in relation to the potential improvement in efficiency of other components such as heat exchangers. Information about entropy production associated with energy dissipation allows for an objective estimation of the optimization potential of each component within an ejector refrigeration cycle. In addition; the improvement due to the specific process control of the ejector cycle compared to the conventional heat pump cycle can be analyzed. The energetic benefit gained using an ejector depends on the refrigerant used. The refrigerants R134a and R744 (CO2) were compared in regard to the entropy production of the heat pump system.

In order to simulate an ejector refrigerant cycle and to evaluate the energy dissipation by means of entropy production; existing models for cycle components were modified. Applying the second law of thermodynamics; local distribution of entropy production as well as the overall entropy produced in each component was determined. The analysis showed that entropy production is caused by two types of effects. One part results from real effects such as pressure drop and heat transfer; the other part is due to the modeling assumptions made. Thus; the investigation of energy dissipation leads to a deeper understanding of the model.

The simulated amount of entropy produced is summarized in a record; so that the results can be read easily by other programs; e.g. programs that visualize energy and entropy flows. In the presented investigation the entropy flow and dissipation effects were analyzed by means of diagrams; such as Sankey diagrams.

The complete heat pump system has been simulated using the Modelica library TIL (TLK-IfT-Library) in order to determine the energy dissipation in each cycle component. With the modified TIL models; other process controls can also be investigated. This approach offers the opportunity to analyze the energy dissipation in detail; and differs in that sense from the commonly used technique of integrated energy balances and COP determinations.

Keywords

Entropy analysis; refrigeration; compression cycle; simulation; CO2; R134a

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