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This paper describes the development of an optimization-friendly thermodynamic property model of water and steam that covers liquid, vapor, 2-phase as well as the super-critical region. All equations are at least twice continuously differentiable with respect to all model variables and can be used in dynamic optimization problems solved by efficient derivativebased algorithms. The accuracy has been verified against the industry standard IAPWS IF97 and performance and robustness have been tested by solving a trajectory optimization problem where the start-up time of a gas power plant has been minimized while satisfying constraints on temperature gradients, pressure and flows. Simulations of various plant models have also been performed to verify and benchmark the implementation. The results show that the new media can be used in both solving dynamic optimization and simulation problems yielding reliable results. The new media has been integrated into Modelon's Thermal Power library 1.13. This article is built upon the work in (Åberg, 2016).

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This paper describes recent advances in simulation of zero flow conditions based on work with Daimler using the Air Conditioning Library from Modelon. The Air Conditioning Library is based on the open standard modelling language Modelica. Simulating refrigerant loops at (near) zero flow for large vapor compression cycles is challenging, due to the fast dynamics in the model under those conditions that drastically reduce the step size of the solver. Findings on solver selection and pressure drop correlations are presented. An approach to improve zero flow simulation based on a systematic analysis of heat transfer coefficients is suggested and demonstrated to increase simulation robustness under (near) zero flow conditions.