Ram N. Singh

The Role of Size Effects on Surface Properties

Abstract A theoretical model based on the grand partition function has been developed to investigate the role of size effects on surface tension and surface segregation of liquid binary alloys. The necessary relation, which connects the surface composition with surface tension through order potential, surface coordination and volume ratio, is obtained. This has been applied to liquid Na-Cs alloys. Likewise bulk properties, surface segregation and surface tension of Na-Cs liquid alloys are also affected appreciably by the size difference and are anomalous around C Na = 0.8.

Higher Order Conditional Probabilities And Short Range Order in Molten Alloys

Abstract A thermodynamic model based on cluster of four atoms is considered with a view to obtain conditional probabilities enumerating the higher order atomic correlations in the nearest neighbour shell of liquid binary alloys. This has helped to discuss as how the higher order atomic correlations in liquid alloys are related to pairwise distribution. The values of order energy, activity and the chemical short range order parameter computed for Bi-Cd, Li-Mg, Cd-Mg, Cd-Ga, Cu-Pb and K-Na are presented.

Specific heat ratio, Grüneisen parameter and Debye temperature of crude oil

There has been substantial interest in determining the thermo-physical properties of hydrocarbon fluids. We have used three different experimental techniques: ultrasonic interferometry to determine the velocity of compressional wave, differential scanning calorimetry to determine the specific heat and the Anton Paar density meter to determine the density of crude oil sample over a wide range of temperatures varying from 20 to 70 °C. These data are used in thermodynamic relations to evaluate the specific heat ratio, the Gruneisen parameter, the Debye temperature and the long wavelength limit of the structure factor. The packing fraction obtained for crude oil is found to be closer to the values of other dense liquid fluids.

Effect of core-ion potentials on thermodynamic properties of liquid alkali metals and alloys

Abstract A pseudopotential perturbation scheme based on Gibbs-Bogoliubov variational technique is considered to investigate the structure and volume dependent contributions to the internal energies of liquid alkali metals. This has paved the way to analyse the effect of core-ion potentials on Helmholtz free energy, enthalpy, pairwise interactions and on entropy of liquids Na, K, Rb and Cs. Excess entropy of mixing for Na-K. Na-Cs and K-Rb are also calculated and are found very sensitive to the core-ion potentials.

A correlation between surface, transport and thermo-elastic properties of liquid hydrocarbon: an experimental investigation

The temperature dependence of surface tension and viscosity has been investigated in two multi-component liquid hydrocarbons, namely, crude oil samples with different API numbers. The surface tension is found to decrease linearly with temperature whereas viscosity exhibits Arrhenius type variation. These measured values along with the ultrasound velocity, density and the isothermal compressibility have been used to estimate a number of physical parameters such as the activation energy, attenuation factor and the shear wave velocity. Crude oil with larger API was found to have smaller activation energy. Shear velocity decreases exponentially with increasing temperature while the attenuation factor is found to increase linearly with temperature. The ratio of the surface tension to viscosity varies linearly as the square root of temperature. The product of the surface tension and the isothermal compressibility, often characterized as a fundamental or correlation length of the surface of the liquid, was found to yield a constant value for both samples.

Equation of State of Crude Oil Samples

Technological advancement in exploration, refinement and enhanced recovery of hydrocarbon fluids heavily depend upon the thermo-physical properties of these fluids under different temperature and pressure conditions. A direct measurement at in-situ conditions is quite difficult; therefore we have utilized thermodynamic equations to extrapolate these thermo-physical properties at ambient conditions. The basic ingredients are density and ultrasound velocity which we have measured in the laboratory as a function of temperature for light and heavy crude oils procured from different wells of Oman. The densities of the samples were measured as a function of temperature using a precision density meter and the sound velocity using an ultrasound interferometer. To understand the variation of physical properties on mixing we have studied a 50:50 mixture of light and heavy oils. These data, in turn, were used to develop the equation of state. Our computed equation of state conforms reasonably well to the in-situ reservoir conditions.

Equation of state of crude oil through temperature dependent ultrasonic measurements

Ultrasound interferometery has been used to determine the velocity of propagation of compressional waves in two different samples of crude oil over a wide range of temperatures. The corresponding bulk density of the samples at similar conditions has also been measured using an Anton Paar density meter. These experimentally measured quantities form the basis for the thermo-physical characterization of crude oil through thermodynamic relations. This facilitated the evaluation of the acoustic impedance, compressibility and the coefficient of thermal expansion as a function of temperature. Simple analytical relations are suggested to describe the temperature dependence of thermo-physical functions. The equation of state for the crude oil has been set up by using these data. Our study yields a very close agreement to the reservoir conditions of the respective oil fields and to other empirical relations.

Thermo-elastic and thermodynamic properties of light and heavy crude oil

Three different experiments, viz., ultrasound interferometry, differential scanning calorimetry, and density measurements were carried out over a wide range of temperature varying from 20°C to 70°C in light, heavy, and a mixture of light and heavy crude oil samples which differ considerably in its American Petroleum Institute gravity. The properties of the mixture have been discussed in terms of its deviation from the ideal values of mixing. The directly measured quantities such as the compression wave velocity, the specific heat at constant pressure, and the density were used to evaluate the temperature dependence of adiabatic compressibility, coefficient of volume expansion and the acoustic impedance. A correlation between thermo-elastic and thermodynamic functions of crude oils has been investigated. In particular, the ratio of the specific heats has been determined by making use of the thermo-elastic functions, which was further used to estimate the specific heat at constant volume. The values of the isothermal compressibility and the coefficient of volume expansion are used to evaluate the pressure–temperature dependence of crude oil conforming to in-situ reservoir conditions.

Chemical and Topological Order in the Vicinity of Phase Separation

A statistical thermodynamic model is used to establish a link between the chemical order, topological order and the concentration fluctuations in the nearest neighbour shell of a binary mixture. The topological order related to density fluctuations is found to play the dominant role in the process of phase separation.

Pressure variation of melting temperatures of alkali halides

The melting temperatures of alkali halides (LiCl, LiF, NaBr, NaCl, NaF, NaI, KBr, KCl, KF, KI, RbBr, RbCl, RbI and CsI) have been evaluated over a wide range of pressures. The solid–liquid transition of alkali halides is of considerable significance due to their huge industrial applications. Our formalism requires a priori knowledge of the bulk modulus and the Gruneisen parameter at ambient conditions to compute Tm at high pressures. The computed values are in very good agreement with the available experimental results. The formalism can satisfactorily be used to compute Tm at high pressures where the experimental data are scanty. Most of the melting curves (Tm versus P) exhibit nonlinear variation with increasing pressure having curvatures downward and exhibit a maximum in some cases like NaCl, RbBr, RbCl and RbI. The values of Tmmax and Pmax corresponding to the maxima of the curves are given.