Variable volume ratio free-piston expander: Prototyping and experimental campaign

•A control strategy for a variable BVR free piston expander is developed.•A test setup has been designed and built.•Dynamic model has been validated.•Cogging force and the frictional force are identified.•Preliminary sizing of an integrated design has been made. This paper describes a dynamic model...

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Bibliographic Details
Published in:International journal of refrigeration 2019-02, Vol.98, p.70-79
Main Authors: Gusev, S., Ziviani, D., Vierendeels, J., De Paepe, M.
Format: Article
Language:English
Subjects:
Algorithms
Alternateur linéaire
Alternators
Cogging
Commande prédictive
Compressors
Control theory
Cycle organique de Rankine à petite échelle
Dynamic models
Détendeur à piston libre
Electric motors
Free-piston expander
Heat recovery
Linear alternator
Mathematical analysis
Model predictive control
Model testing
Prototyping
Rankine cycle
Rapid prototyping
Rapport volumique variable
Refrigeration
Servomotors
Small-scale ORC
Variable built-in volume ratio
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Summary:•A control strategy for a variable BVR free piston expander is developed.•A test setup has been designed and built.•Dynamic model has been validated.•Cogging force and the frictional force are identified.•Preliminary sizing of an integrated design has been made. This paper describes a dynamic model developed for control purposes of a novel free piston expander with a variable built-in volume ratio (BVR) for Organic Rankine Cycle (ORC) applications. In order to demonstrate the feasibility of the proposed concept and to validate the theoretical model, a test setup has been designed and built. An integrated two degree of freedom motor/alternator is substituted by a separate linear motor/alternator (LMA) and a rotary servo motor designed and made from standard industrial components. This approach gives a possibility to develop and to test the integrated alternator and the expander itself independently. The model has been validated by running the setup in compressor mode. The cogging force and the frictional force, which are difficult to obtain analytically, are identified and mapped. An estimation of the geometry and the mass of the piston of an integrated design has also been made. The obtained results are sufficient for the control algorithm development since all acting forces are calculated or estimated with a good accuracy.
ISSN:0140-7007
1879-2081
DOI:10.1016/j.ijrefrig.2018.10.004