Development of New Equation of State by Coordination Number Models
Date Issued
2009
Date
2009
Author(s)
Hsu, Chan-Chia
Abstract
In this work we study the local composition models in existing thermodynamic models and then propose a general way for developing liquid activity coefficient models or equation of state. We found that to develop an activity coefficient model, there are at least two physical concepts needed to be satisfied: (1) the total number of molecules near one certain molecule has to be a constant at any temperature or mixture composition, and (2) the number of molecular pairs should be conserved, that is, the total number of molecule A -B pairs calculated from the local composition of A around B should be the same as that from B around A. We have derived local compositions of most commonly used liquid activity coefficient models, which is only satisfied the concept (1) but concept (2). Therefore, we propose a new local composition model to make sure the concept (2) satisfied and then we solve the temperature and composition dependency from the concept (1), resulting in a new class of excess Gibbs free energy models. Models developed based on this approach are theoretically correct and can be validated using simulation results. Furthermore, the lattice gas theory is applied in this model to develop a new kind of equation of state by adding an imaginary material which represents void sites to the system.
Subjects
local composition model
liquid activity coefficient model
equation of state
lattice gas theory
Type
thesis
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