Papers by Keyword: Activity Coefficient

Abstract: In metallurgical production processes, the vapor pressures and activity coefficients of impurity elements areconsidered as importantparameters in thermodynamic calculation. A saturated flow method was used to measure the dissolution equilibrium of Mn vapour over the surface of liquid Ni-Cr-Co-Mo alloys from 1773 to 1923K, and the measured results were employed in the calculation of the activities andactivity coefficients of Mn in liquid Ni-Cr-Co-Mo alloys. It is found that Mn showed a strong positive deviation from the Henry’s law, and the relationship between temperature and the standard free energy of dissolution reaction Mn(g)=[Mn]_Ni-Cr-Co-Mowas determined to be . At 1873 and 1923K , the activity coefficient ƒof Mn in the Ni-Cr-Co-Mo alloymelt with 0.2wt.%Mn addition were calculated to be 1.065 and 1.068, respectively. According to the results mentioned above,the volatile lower limit of Mn can be up to 2.14 ppm in conventional vacuum melting production.

Abstract: In this work, the CO₂ solubility predicted for amines of DEA and MDEA by using the OConnell (1964) expression as a base model. This expression fits between the solvent compositions and the thermodynamic properties beside the gas solubility. The solvent activity coefficient, Gibbs energy and Henrys law constants have been generated using Aspen plus data analysis tools. The self-interaction binary parameters (Margules parameters) have been calculated based on Henry constants values. The data input for this work depends on the amine system process conditions (temperature range between 298.15 K and 393.15 K), materials composition (concentrations of 10 wt%, 20 w% and 30 wt %). For both of the DEA and MDAE and the pressure fixed to be 101.3 KPa. The solubility values of this work give satisfactory results compared to the literature data.

Abstract: In recent years, liquid desiccant cooling system has shown its potential research value for its low-grade heat using and energy-saving. Thermal properties of liquid desiccant, especially its vapor pressure greatly affects the dehumidification efficiency of this system. Here comes the problem to find a liquid desiccant with better dehumidification effect and lower cost. To solve this problem, a local composition model: nonrandom two-liquid (NRTL) theory could be used to calculate a mixed solution of LiBr-CaCl₂, and calculates the ideal mixing ratio of this solution in a working environment. The best mixing ratio with cost-effectiveness can be worked out by taking into account the initial cost of the solution. Study shows that: compared to single LiBr solution, the dehumidification effect could be raised by more than 8.2% and the costs could be reduced by 20% with mixed LiBr-CaCl₂ solution.

Abstract: This paper proposes a hypothesis of hydration. It assumes that the solute in the electrolyte solution exists as molecules, and each solute molecule is surrounded by h water molecules. On this basis, this paper deduces the activity coefficient formulas, and the model is applied to binary electrolyte solutions at room and elevated temperatures.

Abstract: The steelmaking field has been seeing an increased demand of reducing hydrogen and nitrogen in liquid steel before casting. This is often accomplished by vacuum treatment. This paper focuses on developing a numerical model to investigate the removal of hydrogen and nitrogen from the melt of medium carbon steel in a commercial vacuum tank degasser. An activity coefficient model and the eddy-cell expression are implemented in the ANSYS FLUENT code to compute the activities of related elements and mass transfer coefficients of hydrogen and nitrogen in liquid steel. Several cases are simulated to assess the effect of gas flow rate and initial nitrogen content in liquid steel on degassing process and the calculated results are compared with industrial measured data.

Abstract: The influence of the chemical activity effects on moisture transport in the presence of ions in cementitious materials is studied. Wetting-drying tests are carried out on various hardened concretes (sound and fully carbonated) with water. Moisture profiles are experimentally assessed by gamma-ray attenuation. A multispecies and multiphase numerical model, in which the Lin and Lee approach is applied to compute the chemical activity coefficients of water in presence of ions, is used to simulate the transport of ions and moisture. The drying kinetics is analyzed to assess the intrinsic permeability of the material by inverse analysis. Experimental profiles are compared to the simulations to illustrate the relevance of the modeling.

Abstract: A matrix method for description of some thermodynamic properties in multicomponent alloys in explicit form has been proposed. It has been found that the method for determining thermodynamic properties from the cross-section data allows to find the contribution of short-range ordering into the thermodynamic state of an imperfect alloy. Diffusion processes in alloys are formed both from purely kinetic migrations of particles and from the system's thermodynamic properties. A consequence of this fact is that the diffusion coefficients D in all systems except for perfect solid solutions include to factors being D = Lg , the second one is the thermodynamic factor directly related to the system's chemical potential. However direct experimental separation of these factors can easily be performed in binary systems only while in triple systems in is highly difficult let alone multicomponent systems. Experimental evaluation of the factors in multicomponent systems from short-range order's parameters [1] would allow to establish a relation between the system's thermodynamic properties which is highly important for further progress in multicomponent diffusion theory and for practical applications.

Abstract: In this study, the viscosities and conductivities of bioleaching solution were determined by Ubbelohde viscometer and conductivity meter, respectively. The mean ionic activity coefficients, relative partial molar free energies of copper bioleaching solution at above experimental temperatures ranging from 298 K to 313 K have been calculated. Simultaneously, these characters of copper bioleaching solution were compared with and without mesophilic bacteria. The experimental data showed that the viscosities and thermodynamic properties for bioleaching solution would be crucial to minimize the third phase formation so as to increase extraction efficiency.