Effects of quenching rate and viscosity on spinodal decomposition

Poesio, Pietro; Cominardi, G.; Lezzi, Adriano Maria; Mauri, Roberto; Beretta, Gian Paolo

doi:10.1103/physreve.74.011507

Cited by 32 publications

(43 citation statements)

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“…The reason for such difference in the two otherwise very similar experiments remains unclear, but most likely it is due to the difference in the mixture used. It is worth mentioning however that even for the critical composition mixture we have not seen (using an experimental set-up not described in the paper) a dendritic structure, contrary to what we have seen in our previous work [28]. There may be several reasons for that:…”

Section: Resultscontrasting

confidence: 94%

Heat transfer enhancement in a small pipe by spinodal decomposition of a low viscosity, liquid?liquid, strongly non-regular mixture

Fede

Poesio

Beretta

2012

International Journal of Heat and Mass Transfer

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a b s t r a c tWe report experimental evidence of a 20-40 % enhancement of the effective heat transfer coefficient for laminar flow of a partially miscible binary liquid-liquid mixture in a small diameter horizontal tube that obtains when phase separation occurs in the tube. A mixture of acetone-hexadecane is quenched into the two-phase region so as to induce spinodal decomposition. The heat transfer rate is enhanced by selfinduced convective effects sustained by the free energy liberated during phase separation. The experimental heat transfer coefficients obtained when separation occurs are compared to the corresponding values predicted for flow of a hypothetic mixture with identical properties but undergoing separation. For such comparison, the energy balance equation must carefully take into account both the sensible heat and the excess enthalpy difference between the inlet and the outlet streams because our liquid-liquid binary mixture is a very asymmetric system with large excess enthalpies. The non-ideal mixture thermodynamic properties needed for the energy balance are obtained by an empirical procedure from the experimental data available in the literature for our mixture. The experimental setup and calculation procedure is tested by experiments performed using single-phase water flow and single-phase mixture flow (above the critical point). The convective heat transfer augmentation that results in the presence of liquid-liquid phase separation may be exploited in the cooling or heating of small scale systems where turbulent convection cannot be achieved.

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Section: Resultscontrasting

confidence: 94%

Heat transfer enhancement in a small pipe by spinodal decomposition of a low viscosity, liquid?liquid, strongly non-regular mixture

Fede

Poesio

Beretta

2012

International Journal of Heat and Mass Transfer

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“…Our main experimental result is that the droplet selfpropels around and its radius shrinks with a t 1 scaling, instead of the typical t 1=2 fingerprint of a purely diffusive process (linear or nonlinear diffusion equation neglecting convective terms). The t 1 scaling can only be explained as a consequence of hydrodynamic convective effects due to the motion of the droplet [11,13,18]. Since no flow nor pressure, temperature, nor concentration gradients are present in the background phase B, the droplet motion must be self-generated by dissolution dynamics.…”

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“…To allow visualization, 50 ppm of crystal violet (that preferentially mixes with acetone) are added. Crystal violet is a cationic emulsifier, but at such low concentration it has no effect on the solubility limits [13]. We inject a droplet of either pure hexadecane H or phase A into phase B and observe its time evolution.…”

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confidence: 99%

“…RðtÞ $ À t, and not as RðtÞ $ À t 1=2 as Fickian diffusion as well as the nonlinear B model would predict if convection is neglected. We will show that the scaling law we observe is an effect of the importance of hydrodynamic convection effects during mass transfer [11], generated by the droplet self-propelling around while dissolving [12], caused by Korteweg forces [7,13].In our experiments, we use binary liquid mixtures of acetone and hexadecane because they are partially miscible (Fig. 1) and have density differences lower than 0.1% and negligible excess volume at all compositions; therefore, buoyancy effects can be neglected.…”

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Dissolution of a Liquid Microdroplet in a Nonideal Liquid-Liquid Mixture Far from Thermodynamic Equilibrium

2009

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A droplet placed in a liquid-liquid solution is expected to grow, or shrink, in time as $t 1=2 . In this Letter, we report experimental evidence that when the composition in the interface is far from thermodynamic equilibrium due to the nonideality of the mixture, a droplet shrinks as $t. This scaling is due to the coupling between mass and momentum transfer known as Korteweg forces as a result of which the droplet self-propels around. The consequent hydrodynamic convection greatly enhances the mass transfer between the droplet and the bulk phase. Thus, the combined effect of nonideality and nonequilibrium modifies the dynamical behavior of the dissolving droplet. DOI: 10.1103/PhysRevLett.103.064501 PACS numbers: 47.51.+a, 64.75.Bc, 68.05.Àn The formation and dissolution of gas bubbles and liquid droplets in liquid-gas and liquid-liquid systems are major concerns in many industrial processes as they occur in mixing and separation, in dispersion of food products, and in pharmaceutically controlled drug delivery, for instance. When a gas bubble or a liquid droplet is placed in a gas-liquid or liquid-liquid mixture, it is expected to grow (or to shrink) by diffusion; this process is described by the well-known diffusion equation, as @ 1 =@t ¼ Àr Á j 1 in terms of the local concentration 1 ðr; tÞ and mass flux j 1 of component A in the mixture. If one assumes a binary, ideal mixture, the net mass flux can be calculated by Fick's law, j 1 ¼ ÀD 0 r 1 , where D 0 is the experimentally determined diffusion coefficient. Based on this model, the seminal work by Epstein and Plesset [1], which describes successfully the t 1=2 shrinkage dynamics of a spherical air bubble in an air-water solution, has been recently extended and the t 1=2 scaling experimentally validated also for a liquid droplet (aniline or water) dissolving in a liquidliquid (water-aniline or aniline-water) solution [2].Fickian diffusion, however, is strictly limited to ideal mixtures and cannot hold for multiphase systems, even at thermodynamic equilibrium. A more general formulation for the mass flux can be found by means of nonequilibrium2 are the chemical potentials of the two components, and 1 , 2 , are the mobility (or Onsager) coefficients. While the diffusivity D 0 can be a constant for a binary system, the mobility coefficients are composition dependent [4]. For an ideal mixture or in the dilute limit, this formulation reduces to Fick's law. Following Cahn and Hillard [5], for a heterogeneous system, the local molar Gibbs free-energy g can be written as the sum of a local and a nonlocal contribution: g ¼ g loc þ 1 2 a 2 RTðr Þ 2 , where a is the characteristic length scale of inhomogeneity [6] (different formulations for the free energy have also been developed [9]). Using a mobility coefficient of the form ¼ ð1 À ÞD 0 and assuming the Flory-Huggins local free energy, Mauri et al. [7] proposed the net mass flux j ¼ À ð1 À ÞD 0 r~, with~¼ 0 þ log 1À þ Éð1 À 2 Þ À a 2 r 2 where É is the Margules parameter. As a result, we can write j ¼ ÀD 0 r þ ð1...

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Retardation of the phase segregation of liquid mixtures with a critical point of miscibility

Califano

Mauri

2018

AIChE Journal

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The Phase Transition Extraction (PTE) process consists of bringing a partially miscible mixture from the single-phase to the two-phase region of its phase diagram. Its most important characteristic is that the resulting phase separation is very fast, and hardly affected by coalescence-retarding impurities. In this work we study two counter-cases, where the PTE process appears to be severely retarded. First, we consider the ouzo effect, where the mixture forms very stable metastable micro-emulsions, showing that this process can be generalized, leading to a reverse ouzo effect, where a modifier is added in large quantities. The second retardation technique consists of using very viscous solvents. We found that, in agreement with the predictions of the phase field model, the growth rate of the nuclei during the initial stage of phase separation does not depend on viscosity, while, on the other hand, when the size of the 2 nuclei exceed their capillary length, gravitational effects become relevant and the settling time is proportional to the viscosity of the continuous phase.

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Effects of quenching rate and viscosity on spinodal decomposition

Cited by 32 publications

References 23 publications

Heat transfer enhancement in a small pipe by spinodal decomposition of a low viscosity, liquid?liquid, strongly non-regular mixture

Heat transfer enhancement in a small pipe by spinodal decomposition of a low viscosity, liquid?liquid, strongly non-regular mixture

Dissolution of a Liquid Microdroplet in a Nonideal Liquid-Liquid Mixture Far from Thermodynamic Equilibrium

Retardation of the phase segregation of liquid mixtures with a critical point of miscibility

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