Adsorption in Mixtures with Competing Interactions

A binary mixture of oppositely charged particles with additional short-range attraction between like particles and short-range repulsion between different ones in the neighborhood of a substrate preferentially adsorbing the first component is studied by molecular dynamics simulations. The studied thermodynamic states correspond to an approach to the gas–crystal coexistence. Dependence of the near-surface structure, adsorption and selective adsorption on the strength of the wall–particle interactions and the gas density is determined. We find that alternating layers or bilayers of particles of the two components are formed, but the number of the adsorbed layers, their orientation and the ordered patterns formed inside these layers could be quite different for different substrates and gas density. Different structures are associated with different numbers of adsorbed layers, and for strong attraction the thickness of the adsorbed film can be as large as seven particle diameters. In all cases, similar amount of particles of the two components is adsorbed, because of the long-range attraction between different particles.

Efficient multiscale calculation results for microchannel mass transfer

When the channel height is reduced to a small value such as on the scales of 10 nm or 100 nm, the physical adsorbed layers on the channel walls will participate in the flow, although intermediate between them is a continuum fluid flow. The multiscale simulation results are presented for this multiscale mass transfer in a narrow slit pore based on the derived flow equations. The results are respectively compared with those calculated from conventional continuum flow theory and from the theory based on the solid layer assumption, when the fluid-wall interaction is respectively weak, medium and strong. The total mass flow rate of the two adsorbed layers is also compared with the mass flow rate of the intermediate continuum fluid. The obtained results show the importance of the incorporation of the adsorbed layer flow by the multiscale scheme when calculating the transferred mass in a microchannel.

Thermal, Caloric and Transport Properties of the Lennard–Jones Truncated and Shifted Fluid in the Adsorbed Layers at Dispersive Solid Walls

Fluid properties change when the fluid is adsorbed at a wall. The effect of the adsorption on the fluid properties was studied here by molecular simulation. There is much previous work in this field on fluids in nanochannels that are so small that the adsorbed layers on both walls interfere. In this work, the channel width was so large that the adsorbed layers did not interfere, such that information on the adsorbed layer on single walls was obtained and average values of thermodynamic properties of the fluid in that layer were determined. The studied fluid properties are: pressure p, density ρ, internal energy u, enthalpy h, isobaric heat capacity cp, thermal expansion coefficient αp, thermal conductivity λ, shear viscosity η and self-diffusion coefficient D. For the study, non-equilibrium molecular dynamics simulations were carried out. The fluid and the solid were modelled with the Lennard–Jones potential truncated and shifted at r∗c=2.5σ. The overall density of the fluid was ρ¯=0.8. The overall temperature and the solid–fluid interaction were varied. The corresponding bulk states are liquid or supercritical. The results for the fluid properties in the adsorbed layer were compared to the corresponding bulk values and the deviations are generally below 15%.

Molecular Dynamics Study of Adsorption of the Lennard-Jones Truncated and Shifted Fluid on Planar Walls

A comprehensive molecular dynamics study of gas phase and supercritical fluid adsorption on planar walls in dispersive systems is presented. All interactions in the system are described with the Lennard-Jones truncated and shifted (LJTS) potential with a cutoff radius of 2.5 fluid diameters. The adsorption strength is characterized by the solid-fluid interaction energy and the wall density. Both parameters are varied systematically. The present work extends a previous study in which wetting in the same systems was investigated. Therefore, the contact angles are known for all studied systems. They include cases with total wetting as well as cases with partial wetting. The temperature varies between the triple point and 3 times the critical temperature of the LJTS fluid. For the systems with partial wetting, the adsorption is studied not only up to the saturation pressure but also in the metastable region. For all systems, the surface excess is determined as a function of pressure and temperature. Furthermore, data on the thickness and structure of the adsorbed layers is reported. In some of the systems, prewetting is observed.

INFLUENCE OF CHANNEL GEOMETRY, PRESSURE, TEMPERATURE, OSCILLATIONS AND ADSORPTION ON OBLITERATION OF SLIT SEALS OF ELECTRIC POWER SYSTEMS

The infl uence of the geometric dimensions and confi guration of slot contactless seals on the obliteration of the gaps of plunger pairs at the design and calculation stage of drive systems of electric power systems units is considered. The combined eff ect of working fl uid contamination and the adsorption eff ect on the overgrowth of the living section of the channel was revealed. The fl ow rate during sample shedding was reduced simultaneously as a result of the channel overgrowing with contamination particles and adsorption, i.e. the formation of boundary fi lms on the channel walls. Leaks through the gap at concentric and eccentric position of the plunger in the sleeve are determined. The minimum gap is found, at which the obliteration process is stabilized and loose mud formations are washed away by the fl ow of the working fl uid. The infl uence of the pressure drop at the ends of the slot gap on the channel obliteration process was revealed. With an increase in the pressure drop, the process of stratifi cation of adsorbed layers of polar molecules accelerates, resulting in an increase in the number of contamination particles trapped in the gap per unit of time. With an increase in the temperature of the working fl uid, the process of channel obliteration accelerates, which is confi rmed by experiments. With an oscillating plunger, the fl ow through the annular gap is less than with a stationary one. This is due to the fact that the oscillating plunger occupies a position in the sleeve close to the concentric one, at which leaks are minimal. A stable fl ow rate is obtained when the working fl uid fl ows through the gaps of the plunger pairs performing reciprocating oscillating movements.

INFLUENCE OF CHANNEL GEOMETRY, PRESSURE, TEMPERATURE, OSCILLATIONS AND ADSORPTION ON OBLITERATION OF SLIT SEALS OF ELECTRIC POWER SYSTEMS

The infl uence of the geometric dimensions and confi guration of slot contactless seals on the obliteration of the gaps of plunger pairs at the design and calculation stage of drive systems of electric power systems units is considered. The combined eff ect of working fl uid contamination and the adsorption eff ect on the overgrowth of the living section of the channel was revealed. The fl ow rate during sample shedding was reduced simultaneously as a result of the channel overgrowing with contamination particles and adsorption, i.e. the formation of boundary fi lms on the channel walls. Leaks through the gap at concentric and eccentric position of the plunger in the sleeve are determined. The minimum gap is found, at which the obliteration process is stabilized and loose mud formations are washed away by the fl ow of the working fl uid. The infl uence of the pressure drop at the ends of the slot gap on the channel obliteration process was revealed. With an increase in the pressure drop, the process of stratifi cation of adsorbed layers of polar molecules accelerates, resulting in an increase in the number of contamination particles trapped in the gap per unit of time. With an increase in the temperature of the working fl uid, the process of channel obliteration accelerates, which is confi rmed by experiments. With an oscillating plunger, the fl ow through the annular gap is less than with a stationary one. This is due to the fact that the oscillating plunger occupies a position in the sleeve close to the concentric one, at which leaks are minimal. A stable fl ow rate is obtained when the working fl uid fl ows through the gaps of the plunger pairs performing reciprocating oscillating movements.