Energy efficiency in the industry : Robustness Improvement of a Dynamic Model of Two-Phase Flow

Abstract

The topic of this thesis is related to the robustness of finite-volume flow models involving two-phase flows. These models are especially used in the modelisation of evaporators (and condensers), which can be part of the modelisation of complex thermodynamic systems such as ORC systems. Finite-volume flow models are subject to numerical issues like slow simulations or even simulation failures, which constitute a lack of robustness that affects all the models which the finite-volume flow model is part of. In this paper more robust finite-volume flow models will be presented : a p-x formulation and a bidirectional p-h formulation. First they will be compared to the initial model, a standard p-h formulation, to gauge the gain of robustness they represent. And then these improved finite-volume flow models will be integrated in discretized models of evaporator, and a flooded evaporator model will also be conceived. These new evaporator models will be compared with existing evaporator models in order to determine which of them makes the ORC model the most efficient, and if the improved evaporator models significantly enhance the robustness of these ORC models. Results show that, without increasing the errors in the energy and mass balances, p-x formulation represents a significant gain of robustness, while the bidirectional p-h formulation still experciences lack of robustness. For a complete ORC model, in steady-state conditions, the flooded evaporator is the most suitable evaporator model for an efficient ORC model, while improved discretized evaporators do not improve the simulation quality of these ORC models compared to the initial one.