Observations of Sludge Formation in Group I Base Stock for Lubricants and Thermodynamic Modeling with the SAFT Equation of State
Volume 14, Issue 2, 2017, Pages 33-47
E. Pashai, M. R. Dehghani, F. Feyzi
Abstract Varnish and sludge formation are considered as one of the most common problems in lubrication and hydraulic systems. In order to simulate the condition of sludge formation, base stock lubricant (Group 1 API) has been selected and exposed to heat in a laboratory setup. Sludge formation process accelerated in the laboratory scale and solid liquid equilibrium data were extracted. Then solid-liquid equilibrium has been modeled using SAFT equation of state through sludge formation. The results for prediction of sludge formation showed that the absolute average deviations between experimental and theoretical results were less than 1.4%. The calculated results for solubility coefficient of the oxidation byproducts from SN100 (solvent neutral Group I) base stock in fresh (un-oxidized) oil were in good agreement with the experimental data, and average deviation between calculated and experimental data was less than 6.5%. The amount obtained for binary interaction parameter K_ij was – 0.0447. It is shown that SAFT equation of state has the capability of solid liquid equilibrium.
Prediction of Surface Tension in Single and Mixed Electrolyte Solutions
Volume 10, Issue 4, Autumn 2013, Pages 3-15
M. Dadras, M.R. Dehghani
Abstract In this study, the Langmuir adsorption isotherm has been coupled with activity coefficient models for prediction of surface tension of single and mixed electrolyte solutions. Various activity models such as Meissner, Pitzer and extended UNIQUAC have been used and coupled with Langmuir adsorption isotherm. The model parameters were determined through mathematical optimization using experimental surface tension data of single electrolyte solutions. Absolute average deviation was used as objective function in optimization procedure. The results showed that in the case of single
electrolyte solutions different activity coefficient models have similar capability while in the case of mixed electrolyte solutions, extended UNIQUAC model gives better results.
A Simplified Perturbation Model for Prediction of Mean Ionic Activity Coefficient in Aqueous Electrolyte Solution
Volume 10, Issue 3, Summer 2013, Pages 14-26
E. Salehi, M.R. Dehghani, A.R. Fazlali
Abstract In this work a simplified model based on perturbation theory is presented for prediction of activity coefficient of amino acids and electrolytes in aqueous electrolyte solution. In comparison with previous works, in this model a new hard sphere equation of state has been utilized as a reference term while other interactions such as charge-charge, charge-dipole, dipole-dipole and dipole-induced dipole have been considered as perturbation terms. For simplification, solvent has been considered as dielectric continuum. Finally, aqueous electrolyte solutions containing amino acids have been modeled just using two adjustable parameters. The results have been compared with similar models and it is shown that new hard spheres equation of state shows an improvement in accuracy of the model.
New Perturbation Model for Prediction of Amino Acid and Peptide Activity Coefficients
Volume 9, Issue 2, Spring 2012, Pages 34-42
M. R. Dehghani, E. Salehi, A. R. Fazlali
Abstract In this work, a new thermodynamic model based on the perturbation theory is presented. A new hard spheres equation of state as a reference term is applied to correlate the activity coefficient of amino acids and peptides in binary aqueous
solutions. The new hard sphere equation of state has been recently proposed by Dehghani and Modarress [11] and has been applied for different theories and showed excellent capability. In this model dipole-dipole and Lennard-Jones interactions are considered. The results have been compared with similar models and it is shown that application of the new hard spheres equation of state has caused an improvement in the results of perturbation model.