Miscible liquids, mixing

Positive mixing which applies to systems that, given time, would spontaneously and completely mix. Examples are provided by two gases or two miscible liquids mixing apparatus is used on such systems to accelerate mixing. 

The distribution of velocity components (radial, tangential and axial) under conditions of mixing with baffles in comparison with the conditions of vortex formation is presented in Figure 12. The dashed lines in Figure 12 indicate non-baffled conditions. Comparison of the non-baffled and fully baffled velocity curves (solid line) leads to the following set of conclusions on vortex suppression when dealing with perfectly miscible liquids ... 

An important mixing operation involves bringing different molecular species together to obtain a chemical reaction. The components may be miscible liquids, immiscible liquids, solid particles and a liquid, a gas and a liquid, a gas and solid particles, or two gases. In some cases, temperature differences exist between an equipment surface and the bulk fluid, or between the suspended particles and the continuous phase fluid. The same mechanisms that enhance mass transfer by reducing the film thickness are used to promote heat transfer by increasing the temperature gradient in the film. These mechanisms are bulk flow, eddy diffusion, and molecular diffusion. The performance of equipment in which heat transfer occurs is expressed in terms of forced convective heat transfer coefficients. 

In many instances, two or more miscible liquids must be mixed to give a product of a desired specification, such as, for example, in the blending of petroleum products of different viscosities. This is the simplest type of mixing as it involves neither heat nor mass transfer, nor indeed a chemical reaction. Even such simple operations can however pose problems when the two liquids have vastly different viscosities. Another example is the use of mechanical agitation to enhance the rates of heat and mass transfer between the wall of a vessel, or a coil, and the liquid. Additional complications arise in the case of highly viscous Newtonian and non-Newtonian liquids. 

Intermediate liquid 8 values are obtained by mixing liquids of known solubility parameter SPS makes use of this. The 8 value of the mixture is equal to the volume-weighted sum of the individual component liquid 8 values. Thus, the mass uptake of a miscible liquid mixture by an elastomer may be very much greater than the swelling which would occur in the presence of either one of the constituent liquids alone. The mixture could of course comprise more than two liquid components, and an analogous situation would apply MERL have applied this approach for the offshore oil-production industry to allow realistic hydrocarbon model oils to be developed,basically by mixing one simple aliphatic (paraffinic) hydrocarbon, one naphthenic, and one aromatic to proportions that meet two criteria, namely, that... 

Speed-up of mixing is known not only for mixing of miscible liquids, but also for multi-phase systems the mass-transfer efficiency can be improved. As an example, for a gas/liquid micro reactor, a mini packed-bed, values of the mass-transfer coefficient K a were determined to be 5-15 s [2]. This is two orders of magnitude larger than for typical conventional reactors having K a of 0.01-0.08 s . Using the same reactor filled with 50 pm catalyst particles for gas/Hquid/solid reactions, a 100-fold increase in the surface-to-volume ratio compared with the dimensions of laboratory trickle-bed catalyst particles (4-8 mm) is foimd. 

Campbell, A.N., Kartzmark, E.M., Anand. S.C., Cheng, Y., Dzikowski, H.P., Skrynyk, S.M. (1968) Partially miscible liquid systems the density, change of volume on mixing, vapor pressure, surface tension, and viscosity in the system aniline-hexane. Can. J. Chem. 46, 2399-2407. 

The mixing of two miscible liquids is exothermic (releases heat) since solute-solute attractions are less than the solvent-solute attractions. 

Really soluble or miscible liquid pairs are no good for extraction and washing. When you mix them, they will not form two layers In fact, they ll mix in all proportions. A good example of this is acetone and water. What kinds of problems can this cause Well, for one, you cannot perform any extraction with two liquids that are miscible. 

The fundamentals and numerical treatment ot mixing ot two or more liquid components are described in this section. The simplest fundamental explanation is for two miscible liquid components. For example, the spontaneous mixing of two liquid materials is fundamentally controlled by the free energy of mixing ... 

Liquid-Liquid Extraction Principle. If a liquid solvent which is either immiscible or only partially miscible is mixed with a solution containing solute A, the solute will distribute between the two liquids until equilibrium is established. The solute s concentration in the two phases at equilibrium will depend on its relative affinity for the two solvents. Although... 

When one liquid is added to another, the extent to which they intermix is called miscibility. Typically, liquids that have similcir properties mix well — they re miscible. Liquids with dissimilar properties often don t mix well — they re immiscible. You can summarize this pattern with... 

Mixing processes involved in the manufacture of disperse systems, whether suspensions or emulsions, are far more problematic than those employed in the blending of low-viscosity miscible liquids due to the multi-phasic character of the systems and deviations from Newtonian flow behavior. It is not uncommon for both laminar and turbulent flow to occur simultaneously in different regions of the system. In some regions, the flow regime may be in transition, i.e., neither laminar nor turbulent but somewhere in between. The implications of these flow regime variations for scale-up are considerable. Nonetheless, it should be noted that the mixing process is only completed when Brownian motion occurs sufficiently to achieve uniformity on a molecular scale. 

The volume-related mixing power PIV presents an adequate scale-up criterion only in liquid/liquid dispersion processes and can be deduced from the pertinent process characteristics dpid We ° (dp is the particle or droplet diameter We is the Weber number). In the most common mixing operation, the homogenization of miscible liquids, where a macro- and back-mixing is required, this criterion fails completely [10] ... 

Mixing processes involved in the manufacture of disperse systems, whether suspensions or emulsions, are far more problematic than those employed in the blending of low-viscosity miscible liquids, due to the multiphasic character of the... 

The entropy of a solution is increased by the mixing of solvents, and it is decreased by interactions among the solvent molecules or interactions of solutes with the solvent. The mixing of two miscible liquids is a thermodynamically favorable process because it increases the number of positions available to the molecules. The entropy change on going from the unmixed liquids to the mixed state can be calculated from the expression... 

Lee R. Summerlin, Christie L. t Borgford, and Julie B. Ealy, "Nonadditivity of Volumes," Chemical Demonstrations, A Source-book for Teachers, Vol. 2 (American Chemical Society, Washington, DC, 1988), p. 14. The volume of a solution of two miscible liquids is shown to not equal the sum of the volumes of the individual liquids before mixing. 

In the following the state of the art of microstructured mixing devices is presented. Only the mixing of miscible liquids (and gases) is considered the same micro mixers, however, can usually be used for making liquid/liquid and gas/liquid dispersions, which is outside the scope of this chapter, but certainly is worth consideration in the future. If not otherwise mentioned, liquid mixing is involved. The few examples on gas mixing are explicitly dealt with. 

The double-pipe mixer was designed and so far only used for contacting and reacting immiscible fluids [134], The respective flow-pattern maps were derived and annular and slug flows as well as complete spread of the inner-tube fluid were identified as distinct regimes. Since in this chapter only miscible liquids are concerned, no protocol and no results are given for the mixer below. H owever, the device is mentioned, since it could in principle be used also for mixing miscible fluids. 

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