We present coefficients for transfer of heat and mass across the liquid–vapor interface of a one-component fluid. The coefficients are defined for the Gibbs surface from nonequilibrium thermodynamics ...and determined by nonequilibrium molecular dynamics simulations. The main conductivity coefficients are found to become large near the critical point, consistent with the disappearance of the surface in this limit. The resistivities of transfer found by molecular dynamics simulations are compared to the values predicted by kinetic theory. The main resistivity to heat transfer is found to agree from the triple point to about halfway to the critical point. The resistivity to mass transfer was used to determine the condensation coefficient, which was found to be practically constant with a value of about 0.82. The resistivity coupling coefficient predicted by simulations also agrees with values predicted by kinetic theory from the triple point until about halfway to the critical point.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We present evidence for the hypothesis of local equilibrium for a liquid–vapor interface in a one-component fluid, using molecular dynamics simulations. Lennard-Jones/spline particles are studied in ...a two-phase system that is out of global equilibrium. Equilibrium simulations are first used to establish the equation of state for the vapor and interface. A procedure is developed to define the boundaries of the interface. Finally it is shown that the equation of state for the interface applies also when there is heat and mass transport through the interface. The temperature gradient in the vapor was 108 K/m in these studies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
For interactive multimedia and multimedia streams, the receiver playout buffers are required to smooth network delay variations. Instead of using a constant playout speed, newer receiver buffer ...algorithms control the playout speed, which can give a lower end-to-end delay and fewer packets that are lost because of late arrivals. This paper presents a statistically optimal algorithm to control playout speed. The most significant difference to other published playout speed adjusting algorithms is the thorough mathematical approach that this work is based on. A stringent notation and stringent mathematical models of the media receiver system have been developed, which are generic and independent of the networks and protocols used. This has enabled the authors to deduce the statistically optimal controller for the playout speed, which is also independent of the networks and protocols used. Three deviations from perfect playout have been identified: (i) buffering delay, (ii) a playout rate different from the sender rate and (iii) a change of playout rate.
Molecular dynamics simulations were carried out for a binary fluid mixture in a slit pore. The fluid was an argon-like Lennard-Jones /spline model. The pore wall was represented by the Steele model ...for a layered graphite structure. The pore had a heat source in one end and a heat sink in the other, resulting in a lateral temperature gradient, a Soret effect, and a thermal creep flow along the pore wall. Potential models with various depths were used to examine the effect of wetting and adsorption on the thermal creep flow. The main results were as follows. (a) A relatively strong creep flow was generated parallel to the wall by the temperature gradient. For strongly attracting fluid-wall potentials, the flow occurred from the cold to the hot end of the pore near the wall (except for the very narrow pore) and oppositely in the center of the pore. For a purely repulsive potential, the flow was weak and mostly in the opposite direction. (b) The thermal diffusion coefficient was comparable to that in bulk fluid at the same overall density, except when the creep flow was strong, in which case the thermal diffusion was blurred by the convective mixing.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Coupled transport phenomena across a gas/liquid interface, relevant for distillation, were studied by nonequilibrium molecular dynamics simulations. The simulations were set in the context of bulk ...irreversible thermodynamics. It was then shown that mole fraction profiles in the liquid phase and the gas phase of ideal isotope mixtures are linear. For nonideal mixtures, Fick's law cannot be applied in the interface region, because the activity coefficients change dramatically across the interface. Fourier's law has a constant heat conductivity for both types of liquid mixtures but not for gas mixtures. The coupling between heat and mass transfer becomes negligible for distillation in the special case of ideal mixtures with constant molal overflow. In all other cases, the heat of transfer contributes significantly to the heat flux and causes deviations from Fourier's law in the gas phase. This all means that coupled flux equations are needed to describe distillation and that the properties of the surface are important for a description of the heat and mass fluxes involved. The value of the heat of transfer has a bearing on the calculation of the number of theoretical stages in the column. When considered as a function of distance from the surface, the local entropy production rate has a peak or a shoulder (depending on the conditions) slightly into the vapor. The entropy production rate in the liquid cannot be neglected compared to that of the gas. The second law efficiency of distillation was quantified from this knowledge.
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