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ABSTRACT The penetration rate of power-law non-Newtonian liquids in a circular tube driven by the capillary pressure is derived. The dimensionless fractional height of liquid in the tube relative to the equilibrium height, χ = h(t)/h(∞),... more
ABSTRACT The penetration rate of power-law non-Newtonian liquids in a circular tube driven by the capillary pressure is derived. The dimensionless fractional height of liquid in the tube relative to the equilibrium height, χ = h(t)/h(∞), is calculated as a function of an appropriately chosen dimensionless time, permitting expression of the height-time dependence as a function of the reciprocal of the exponent in the power-law model, s = 1/n. It is found that the rate of penetration and, therefore, also withdrawal of liquid is dramatically retarded as the liquid becomes more strongly shear-thinning, i.e., as n becomes small relative to unity.
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The structure of hydrogen chloride (dimer, crystal lattice and liquid) has been calculated using an intermolecular potential model that consists of a central Lennard-Jones (12, 6) part, a polarizable dipole and a permanent quadrupole.... more
The structure of hydrogen chloride (dimer, crystal lattice and liquid) has been calculated using an intermolecular potential model that consists of a central Lennard-Jones (12, 6) part, a polarizable dipole and a permanent quadrupole. Good agreement with available experimental data and quantum mechanical results is obtained for all three structures. In addition the potential model gives satisfactory results for the pressure second virial coefficient. Previous potential models for HCl have been unable to reproduce the liquid structure very accurately.
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Molecular simulations using the method of molecular dynamics have been carried out to determine if external fields can be used to increase the efficiency of membrane-based separation processes, examining both direct and several... more
Molecular simulations using the method of molecular dynamics have been carried out to determine if external fields can be used to increase the efficiency of membrane-based separation processes, examining both direct and several alternating electric fields, and across a range of frequencies. The results show that alternating electric fields have considerable promise as a valuable, yet generally neglected, tool for
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... 7. S. Murad, P. Ravi and JG Powles, J. Chem. Phys., 98 (1993) 9971. 8. S. Murad and JG Powles, J. Chem. Phys., 99 (1993) 7271. 9. S. Murad, Adsorption, 2 (1996) 95; F. Paritosh and S. Murad, AIChE J., 42 (1996) 2984. 10. ...
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A novel computer simulation technique for studying fluids in confined geometries has been developed and used to replicate Pfeffer’s experiment on osmosis in semipermeable membranes in 1877. Our results confirm the validity of van’t Hoff’s... more
A novel computer simulation technique for studying fluids in confined geometries has been developed and used to replicate Pfeffer’s experiment on osmosis in semipermeable membranes in 1877. Our results confirm the validity of van’t Hoff’s famous relationship for osmotic pressure over a wide range of concentrations, and also clearly establish its validity even for molecular systems. We believe this is the first theoretical validation of this result for such a wide range of concentrations, where no explicit assumption of ideality is made for the interactions of the solute molecules.
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The effect of external electric fields on enhancing ion mobility, drift velocity, and drift diffusion as a function of solution concentration has been investigated using molecular dynamics simulations. Our results show that the unusual... more
The effect of external electric fields on enhancing ion mobility, drift velocity, and drift diffusion as a function of solution concentration has been investigated using molecular dynamics simulations. Our results show that the unusual nonlinear behavior observed when the solution concentration matches seawater is also observed when the concentration is reduced to half of that value. These results are of significance in designing processes for desalinating seawater using electro-deionization in which the concentration would decrease during salt removal, and for purification of brackish waters which also have lower salt content.
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We present a simple molecular dynamics (MD)-based method for determining the Henry’s constant and gas-solubility in liquids and have applied it to the case of oxygen dissolved in liquid benzene. This method is an extension of an algorithm... more
We present a simple molecular dynamics (MD)-based method for determining the Henry’s constant and gas-solubility in liquids and have applied it to the case of oxygen dissolved in liquid benzene. This method is an extension of an algorithm we presented earlier to study osmosis and reverse osmosis in liquid solutions and gaseous mixtures. It is based on separating a gaseous
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Molecular simulations using the method of molecular dynamics have been carried out to examine the role that external magnetic fields can play in the transport of water via reverse osmosis (RO) across membranes. Our results show that... more
Molecular simulations using the method of molecular dynamics have been carried out to examine the role that external magnetic fields can play in the transport of water via reverse osmosis (RO) across membranes. Our results show that magnetic fields can increase the transport rate of water across such membranes significantly. These observations can have an important impact on making RO separation processes that involve the removal of water from solutions more efficient, since low flux rates across membranes is an important problem encountered in most current RO processes. We are aware of no experimental studies of such effects.
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ABSTRACT The penetration rate of power-law non-Newtonian liquids in a circular tube driven by the capillary pressure is derived. The dimensionless fractional height of liquid in the tube relative to the equilibrium height, χ = h(t)/h(∞),... more
ABSTRACT The penetration rate of power-law non-Newtonian liquids in a circular tube driven by the capillary pressure is derived. The dimensionless fractional height of liquid in the tube relative to the equilibrium height, χ = h(t)/h(∞), is calculated as a function of an appropriately chosen dimensionless time, permitting expression of the height-time dependence as a function of the reciprocal of the exponent in the power-law model, s = 1/n. It is found that the rate of penetration and, therefore, also withdrawal of liquid is dramatically retarded as the liquid becomes more strongly shear-thinning, i.e., as n becomes small relative to unity.
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Page 1. PINSTECH/NPD-124 MOLECULAR DYNAMICS! APPLICATION TO LIQUID SODIUM Kbawaja Yaldram Abdullah Sadiq Sohail Murad li ( ii I tk > >\ ! ? 1 ! I / \ ! j I ! ! il: M; NUCLEAR PHYSICS DIVISION Pakistan Institute ...
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Molecular dynamics simulations have been used to investigate the effect of confinement on solvation (hydration shell) and solubility of electrolyte solutions (NaCl) confined in nanopores. The co-ordination number and solubility of NaCl in... more
Molecular dynamics simulations have been used to investigate the effect of confinement on solvation (hydration shell) and solubility of electrolyte solutions (NaCl) confined in nanopores. The co-ordination number and solubility of NaCl in water confined in graphitic slit nanopores ...
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... 20 m sl, and droplet size about 5 nm is shown in figure 2. It is seen that the droplets move closer to each other until about 40 000 timesteps, corresponding roughtly to 340ps, and then begin to show signs of bouncing back. After ...
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... This was also in part financed by UKC. Finally, we thank Mr AD Smith and Mr JBWWebber for advice and assistance in the installation and operation of the computer system. References [1] RAHMAN, A., 1964, Phys. Rev. A, 136, 405. ...
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Using molecular simulations, we have investigated heat transfer across the solid–fluid interface of a silica wafer in contact with water vapor. Our results show that the thermal or Kapitza resistance decreases significantly, as the... more
Using molecular simulations, we have investigated heat transfer across the solid–fluid interface of a silica wafer in contact with water vapor. Our results show that the thermal or Kapitza resistance decreases significantly, as the surface becomes more hydrophilic. This is primarily due to increases in adsorption and absorption at the surface, which enhances the intermolecular collision frequency at the interface. Increasing this frequency also reduces the dependence of thermal transport on variations in the interfacial temperature and ...
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Gas separations with faujasite zeolite membranes have been examined using the method of molecular dynamics. Two binary mixtures are investigated, oxygen/nitrogen and nitrogen/carbon dioxide. These mixtures have been found experimentally... more
Gas separations with faujasite zeolite membranes have been examined using the method of molecular dynamics. Two binary mixtures are investigated, oxygen/nitrogen and nitrogen/carbon dioxide. These mixtures have been found experimentally to exhibit contrasting behavior. In O2/N2 mixtures the ideal selectivity (pure systems) is higher than the mixture selectivity, while in N2/CO2 the mixture selectivity is higher than the ideal selectivity. One of the key goals of this work was to seek a fundamental molecular level understanding of such divergent behavior. Our simulation results (using previously developed intermolecular models for both the gases and zeolites investigated) were found to replicate this experimental behavior. By examining the loading of the membranes and the diffusion rates inside the zeolites, we have been able to explain such contrasting behavior of O2/N2 and N2/CO2 mixtures. In the case of O2/N2 mixtures, the adsorption and loading of both O2 and N2 in the membrane are quite competitive, and thus the drop in the selectivity in the mixture is primarily the result of oxygen slowing the diffusion of nitrogen and nitrogen somewhat increasing the diffusion of oxygen when they pass through the zeolite pores. In N2/CO2 systems, CO2 is rather selectively adsorbed and loaded in the zeolite, leaving very little room for N2 adsorption. Thus although N2 continues to have a higher diffusion rate than CO2 even in the mixture, there are so few N2 molecules in the zeolite in mixtures that the selectivity of the mixture increases significantly compared to the ideal (pure system) values. We have also compared simulation results with hydrodynamic theories that classify the permeance of membranes to be either due to surface diffusion, viscous flow, or Knudsen diffusion. Our results show surface diffusion to be the dominant mode, except in the case of N2/CO2 binary mixtures where Knudsen diffusion also makes a contribution to N2 transport.