Multiparameter equations of state for selected siloxanes |
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| Institution: | 1. Process and Energy Department, Delft University of Technology, Leeghwaterstraat 44, 2628 CA Delft, The Netherlands;2. Dipartimento di Ingegneria Aerospaziale, Politecnico di Milano, Via La Masa 34, 20154 Milano, Italy;3. Physical and Chemical Properties Division, National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80305, USA;1. Institute for Thermodynamics, Bundeswehr University Munich, Werner-Heisenberg-Weg 39, 85577 Neubiberg, Germany;1. Department of Mechanical, Chemical and Materials Engineering, University of Cagliari, Via Marengo 2, 09123 Cagliari, Italy;2. Chair of Engineering Thermodynamics and Transport Processes (LTTT), Center of Energy Technology (ZET), University of Bayreuth, Universitätstraße 30, 95440 Bayreuth, Germany;3. Department of Mechanical Engineering, Federal University of Petroleum Resources, Effurun, P.M.B. 1221 Effurun, Delta State, Nigeria |
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| Abstract: | This article presents the development of technical equations of state for four siloxanes using the 12-parameter Span–Wagner functional form. Siloxanes are used as heat transfer fluids and working media in energy conversion applications. The investigated fluids are two linear dimethylsiloxanes, namely MM (hexamethyldisiloxane, C6H18OSi2) and MD4M (tetradecamethylhexasiloxane, C14H42O5Si6), and two cyclic dimethylsiloxanes, namely D4 (octamethylcyclotetrasiloxane, C8H24O4Si4) and D5 (decamethylcyclopentasiloxane, C10H30O5Si5). Available measured properties are critically evaluated and selected for the optimization of the equation of state (EoS) parameters. Due to the insufficient number of experimental values, several other properties are estimated with the most accurate ad hoc methods. These estimates are included in the optimization of the equation of state parameters. Moreover, experimental saturated liquid density and vapor pressure data are correlated with the equations proposed by Daubert and Wagner–Ambrose, respectively, to provide short, simple, and accurate equations for the computation of these properties. The performance of the obtained equations of state is assessed by comparison with experimental data and also with estimates obtained with the Peng–Robinson cubic EoS with the modification proposed by Stryjek and Vera. This equation was adopted in previous technical studies. The improvements obtained with the newly developed EoS's are significant. Exemplary state diagrams are also reported as a demonstration of the consistency of the obtained thermodynamic models. Sound speed measurements in the vapor phase are planned for the near future and results will be incorporated in future improvements of the newly developed thermodynamic models. |
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