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A computationally efficient and accurate numerical representation of thermodynamic properties of steam condensing steam flow in steam turbines
Hrubý, Jan
Mathematical modeling of the non-equilibrium condensing transonic steam flow in the complex 3D geometry of a steam turbine is a demanding problem both concerning the physical concepts and the required computational power. Available accurate formulations of steam properties IAPWS-95 and IAPWS-IF97 require much computation time. For this reason, the modelers often accept the unrealistic ideal-gas behavior. Here we present a computation scheme based on a piecewise, thermodynamically consistent representation of the IAPWS-95 formulation. Density and internal energy are chosen as independent variables to avoid variable transformations and iterations. On the contrary to the previous Tabular Taylor Series Expansion Method, the pressure and temperature are continuous functions of the independent variables, which is a desirable property for the solution of the differential equations of the mass, energy, and momentum conservation for both phases.
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Modelling of water transport in the polymer electrolyte membrane of a fuel cell
Šimek, M. ; Němec, Tomáš ; Maršík, František
A brief review of recent literature on proton exchange membrane fuel cell (PEMFC) modelling is presented and the governing equations of the transport processes in the proton exchange membrane are presented. Consequently, the model of water transport in the membrane electrode assembly of a fuel cell in commercial software FLUENT is investigated. The aim of this work is to test the possibilities of the PEMFC modelling using FLUENT. Special attention is given to the water management and the properties of the fuel cell membrane.of four binary mixtures, i.e. diethylether - nitrogen, propane - carbon dioxide, isobutane - carbon dioxide, and chlorodifluoromethane - carbon dioxide. The predictions of the classical nucleation theory show very good agreement with the measured nucleation rates.
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Klasická nukleační teorie a modelování kavitačních jevů
Němec, Tomáš
The description of the nucleation of bubbles and their growth in cavitation processes suitable for computational fluid dynamics (CFD) simulations is investigated. The number of newly created bubbles and their sizes are treated empirically in most of the numerical codes. We show that the Classical Nucleation Theory (CNT) can be used to calculate the nucleation probabilities in water. Also a simple model of the growth of the nucleated bubbles is described. The CNT predictions of the nucleation rate show promising results and together with the bubble growth model can be used to enhance the precision of CFD modeling of cavitating flows.
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