A Model for Estimation of Viscosity of Molten Silicate Slag
ABSTRACT A model to evaluate the viscosity of silicate melts is proposed on the basis of the bonding states of oxygen, i.e. non-bridging oxygen and free oxygen ions, in the silicate structure, considering the flow mechanism of the melts with the network structure. Gaye's model is applied to evaluate the bonding state of oxygen ions using thermodynamic databases. The present model can reproduce the composition dependence of the viscosities for silicate melts in binary systems with a single model parameter, as well as the composition dependence of the viscosities for ternary systems in a wide composition range.
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ABSTRACT: A model has been developed that links the viscosities of silicate melts to their thermodynamic properties. Over the past several years, through critical evaluation of all available thermodynamic and phase equilibrium data, we have developed a quantitative thermodynamic description of multicomponent silicate melts using the Modified Quasichemical Model for short-range ordering. The local structure of the liquid, in terms of the bridging behavior of oxygen, calculated using our thermodynamic model allows us to characterize the structure of the liquid semi-quantitatively using the concepts of Q-species and connectivity of Q-species. The viscosity is modeled by optimizing viscosity parameters that are related to the structure of the liquid. The viscosity of pure liquid silica is modeled using four model parameters and every other unary liquid is modeled using two. The viscosity of all binary liquids is reproduced within experimental accuracy by optimizing one or at most two binary viscosity parameters for each system. In the present article the equations for the viscosity model are derived and analyses for the experimentally well-established systems CaO-SiO2 MgO-SiO2, NaO0.5-SiO2, KO0.5-SiO2 and AlO1.5-SiO2 are presented. This is the first step in the development of a predictive model for the viscosity of multicomponent silicate melts that will be presented in part II.International Journal of Materials Research (formerly Zeitschrift fuer Metallkunde) 11/2008; 99(11):1185-1194. DOI:10.3139/146.101752 · 0.68 Impact Factor
- International Journal of Materials Research (formerly Zeitschrift fuer Metallkunde) 11/2008; 99(11):1195-1209. DOI:10.3139/146.101753 · 0.68 Impact Factor
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ABSTRACT: The viscosity of slag and the thermal conductivity of ash deposits are among two of the most important constitutive parameters that need to be studied. The accurate formulation or representations of the (transport) properties of coal present a special challenge of modeling efforts in computational fluid dynamics applications. Studies have indicated that slag viscosity must be within a certain range of temperatures for tapping and the membrane wall to be accessible, for example, between 1,300 °C and 1,500 °C, the viscosity is approximately 25 Pa·s. As the operating temperature decreases, the slag cools and solid crystals begin to form. Since slag behaves as a non-linear fluid, we discuss the constitutive modeling of slag and the important parameters that must be studied. We propose a new constitutive model, where the stress tensor not only has a yield stress part, but it also has a viscous part with a shear rate dependency of the viscosity, along with temperature and concentration dependency, while allowing for the possibility of the normal stress effects. In Part I, we reviewed, identify and discuss the key coal ash properties and the operating conditions impacting slag behavior.Energies 02/2013; 6(2):807-838. DOI:10.3390/en6020807 · 1.60 Impact Factor