Comparison of Moving Boundary and Finite-Volume Heat Exchanger Models in the Modelica Language

Adriano Desideri, Bertrand Dechesne, Jorrit Wronski, Martijn Van den Broek, Sergei Gusev, Vincent Lemort and Sylvain Quoilin
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Adriano Desideri: Thermodynamics laboratory, University of Liege, Campus du Sart Tilman, B-4000 Liege, Belgium
Bertrand Dechesne: Thermodynamics laboratory, University of Liege, Campus du Sart Tilman, B-4000 Liege, Belgium
Jorrit Wronski: IPU Engineering Consultant, DK-2800 Kongens Lyngby, Denmark
Martijn Van den Broek: Department of Flow heat and combustion Mechanics, University of Gent, 9052 Gent, Belgium
Sergei Gusev: Department of Flow heat and combustion Mechanics, University of Gent, 9052 Gent, Belgium
Vincent Lemort: Thermodynamics laboratory, University of Liege, Campus du Sart Tilman, B-4000 Liege, Belgium
Sylvain Quoilin: Thermodynamics laboratory, University of Liege, Campus du Sart Tilman, B-4000 Liege, Belgium

Energies, 2016, vol. 9, issue 5, 1-18

Abstract: When modeling low capacity energy systems, such as a small size (5–150 kW el ) organic Rankine cycle unit, the governing dynamics are mainly concentrated in the heat exchangers. As a consequence, the accuracy and simulation speed of the higher level system model mainly depend on the heat exchanger model formulation. In particular, the modeling of thermo-flow systems characterized by evaporation or condensation requires heat exchanger models capable of handling phase transitions. To this aim, the finite volume (FV) and the moving boundary (MB) approaches are the most widely used. The two models are developed and included in the open-source ThermoCycle Modelica library. In this contribution, a comparison between the two approaches is presented. An integrity and accuracy test is designed to evaluate the performance of the FV and MB models during transient conditions. In order to analyze how the two modeling approaches perform when integrated at a system level, two organic Rankine cycle (ORC) system models are built using the FV and the MB evaporator model, and their responses are compared against experimental data collected on an 11 kW el ORC power unit. Additionally, the effect of the void fraction value in the MB evaporator model and of the number of control volumes (CVs) in the FV one is investigated. The results allow drawing general guidelines for the development of heat exchanger dynamic models involving two-phase flows.

Keywords: organic Rankine cycle (ORC); dynamic modeling; dynamic validation; Modelica (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2016
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (19)

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