Title: Optimization-friendly thermodynamic properties of water and steam
Authors: Marcus Åberg, Johan Windahl, Håkan Runvik and Fredrik Magnusson
Abstract: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 derivative-based algorithms. The accuracy has been verified against the industry standard IAPWS 97 and performance and robustness has 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.
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Title: Modeling of a Thermosiphon to Recharge Phase Change Material Based Thermal Battery for a Portable Air Conditioning Device
Authors: Rohit Dhumane, Jiazhen Ling, Vikrant Aute and Reinhard Radermacher
Abstract:Closed loop two phase thermosiphons have a wide range of applications due to their simplicity, reliability, low cost and the ability of dissipating high heat fluxes from minimal temperature differences. The present study focuses on one thermosiphon operation which solidifies a phase change material (PCM) based thermal battery for a portable air conditioner called Roving Comforter (RoCo). RoCo uses vapor compression cycle (VCC) to deliver cooling and stores the heat released from the condenser into a compact phase change material (PCM) based thermal battery. Before its next cooling operation, the PCM needs to be re-solidified. This is achieved by the thermosiphon, which operates within the same refrigerant circuitry with the help of a pair of valves. The molten PCM which acts as heat source affects the dynamics of the thermosiphon which in turn affects the solidification process. Thus the dynamics of both the PCM and thermosiphon are coupled. For accurate transient modeling of this process, the PCM model considers the solidification over a temperature range, variable effects of conduction and natural convection during the phase change and variable amounts of heat release at different temperatures within the temperature range of phase change. The paper discusses component modeling for this transient operation of thermosiphon and its validation with experimental data.
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Title: Extended Modelica Model for Heat Transfer of Two-Phase Flows in Pipes Considering Various Flow Patterns
Authors: Timm Hoppe, Friedrich Gottelt and Stefan Wischhusen
Abstract:Boiling in vertical and horizontal pipes is a complex process defining transient and static performance of various technical applications. An extensive literature review taking all relevant boiling regimes is presented. The models from the literature are evaluated with respect to accuracy and suitability for system simulation application. A set of sub-models for each of the existing boiling phenomena is implemented and applied to a global boiling model. The work pays special attention to smooth transition between the sub-models and to numerical efficient solutions with respect to the consideration of the boiling crisis.
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