728 research outputs found
Comparative Study on Several Criteria for Non-equilibrium Phase Separation
Several different kinds of criteria for non-equilibrium phase separation to
discriminate the two stages, the spinnodal decompostion (SD) and domain growth
(DG), are compared and further investigated. The characteristic domain size and
morphological function present two geometric criteria. Both of them can only
provide rough estimations for the crossover from SD to DG. The reason for
domain size is that the crossover in this description covers a process, instead
of a specific time. The reason for the morphological function is that the
result may rely on chosen threshold value. However, both the non-equilibrium
strength and the entropy production rate are physical criteria and are more
convenient to provide critical times. In fact, not only the non-equilibrium
strength defined in the moment space opened by all the independent components
of the used non-equilibrium quantities but also those defined in its subspaces
can be used as criteria. Each of those criteria characterizes the phase
separation process from its own perspective. Consequently, the obtained
critical times may show slight differences. It should be pointed out that these
slight differences are not contradictive, but consistent with each other and
complementary in describing the complex phenomena.Comment: arXiv admin note: text overlap with arXiv:1808.0769
Discrete Boltzmann modeling of multiphase flows: hydrodynamic and thermodynamic non-equilibrium effects
A discrete Boltzmann model (DBM) is developed to investigate the hydrodynamic
and thermodynamic non-equilibrium (TNE) effects in phase separation processes.
The interparticle force drives changes and the gradient force, induced by
gradients of macroscopic quantities, opposes them. In this paper, we
investigate the interplay between them by providing detailed inspection of
various non-equilibrium observables. Based on the TNE features, we define a TNE
strength which roughly estimates the deviation amplitude from the thermodynamic
equilibrium. The time evolution of the TNE intensity provides a convenient and
efficient physical criterion to discriminate the stages of the spinodal
decomposition and domain growth. Via the DBM simulation and this criterion, we
quantitatively study the effects of latent heat and surface tension on phase
separation. It is found that, the TNE strength attains its maximum at the end
of the spinodal decomposition stage, and it decreases when the latent heat
increases from zero. The surface tension effects are threefold, to prolong the
duration of the spinodal decomposition stage, decrease the maximum TNE
intensity, and accelerate the speed of the domain growth stage.Comment: 10 pages, 10 figure
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