Drop breakup turbulence

Bubble and drop breakup is mainly due to shearing in turbulent eddies or in velocity gradients close to the walls. Figure 15.11 shows the breakup of a bubble, and Figure 15.12 shows the breakup of a drop in turbulent flow. The mechanism for breakup in these small surface-tension-dominated fluid particles is initially very similar. They are deformed until the aspect ratio is about 3. The turbulent fluctuations in the flow affect the particles, and at some point one end becomes... 

Figure 15.12 Breakup of an octanol drop in turbulent water (From [8]).

Dronedarone, 5 103, 106 Drop breakage, 16 696-697 Drop breakup, by turbulence, 16 697 Drop diameter, 10 763-764 Drop dispersions, 10 755 nonuniformity of, 10 765... 

Sevik and Park (S9) suggested that resonance can cause bubble and drop breakup in turbulent flow fields when the characteristic turbulence frequency matches the lowest or natural frequency mode of an entrained fluid particle. Breakup in turbulent flow fields is discussed below. 

Most correlations show that di2 is proportional to the Weber number raised to the power of -0.6, which is consistent with the theory of drop breakup by turbulent shear forces. Strictly, these correlations should be applied only where the drop size is in the inertial subrange of turbulence, i.e.,... 

R. V. Calabrese, C.Y. Wang, and N.P. Bryner, Drop breakup in turbulent... 

Calabrese RV, Chang TPK, and Dang PT. Drop breakup in turbulent stirred-tank contactors. Part I Effect of dispersed-phase viscosity. AIChE J 1986 32 657-666. 

Calabrese RV, Wang CY, and Bryner NP. Drop breakup in turbulent stirred-tank. Part III Correlations for mean size and drop size distributions. AIChE J 19S6 32 677-681. 

A rational theoretical treatment of the dynamics of drop breakup and drop coalescence in a turbulent agitated dispersion requires a fundamental knowledge of the behavior of the flow field. Accordingly, in this section, an introduction to turbulence phenomena and isotropic turbulent behavior is presented with recent pertinent findings included. Studies on the actual... 

Delichatsios and Probstein (D4-7) have analyzed the processes of drop breakup and coagulation/coalescence in isotropic turbulent dispersions. Models were developed for breakup and coalescence rates based on turbulence theory as discussed in Section III and were formulated in terms of Eq. (107). They applied these results in an attempt to show that the increase of drop sizes with holdup fraction in agitated dispersions cannot be attributed entirely to turbulence dampening caused by the dispersed phase. These conclusions are determined after an approximate analysis of the population balance equation, assuming the size distribution is approximately Gaussian. 

Equation (35) for drop breakup caused by acceleration and Eqs. (37) to (39) to model drop breakup by turbulent stresses can be used to interpret drop behavior for the twin-fluid nozzle shown in Figure 7. The predicted size of the ethanol drops dispersed in supercritical carbon dioxide is compared with measured values in Figure 13. One can see that the model predicts well the... 

Kolmogorov AN. The local structure of turbulence in incompressible viscous fluid for very large Reynolds number. Dokl Akad Nauk SSSR 1941 30 301-305. Baldyga J, Podgorska W. Drop breakup in intermittent turbulence. Maximum stable and transient sizes of drops. Can J Chem Eng 1998 76 456-470. 

PIm, power per mass (W/kg). The maximum value for this parameter is calculated for the zone with the highest degree of turbulence. In most cases it takes place in the vortices formed behind the impeller blades. The most important microscale phenomena, such as drop breakup, breaking of crystals, nucleation, and efficient micromixing, take place in these zones. The ratio (P/m) / P/m) is one of the reactor s fingerprints. 

Of special interest is the process of drop breakup in a turbulent gas flow. An expression for the dynamic thrust acting on the drop surface in an isotropic turbulent flow of gas is obtained in [2] ... 

The technological framework is plenty of emulsification approaches, mostly involving mixing two liquids in bulk processes, and many of them using turbulence to enhance drop breakup. 

Davies (10) concluded that it is the turbulent fluctuation velocity 6 that is responsible for drop breakup. The dissipation term is given by the following relation ... 

Keywords Atomization Chemical reactions Craiservation equations Constitutive equations Drop breakup Drop deformation Drop collisions Evaporation LES Newtonian fluids RANS Spray modeling Spray PDF Stochastic discrete particle method Source terms Turbulence... 

The remainder of the chapter focuses on the actual spray modeling. The exposition is primarily done for the RANS method, but with the indicated modifications, the methodology also applies to LES. The liquid phase is described by means of a probability density function (PDF). The various submodels needed to determine this PDF are derived from drop-drop and drop-gas interactions. These submodels include drop collisions, drop deformation, and drop breakup, as well as drop drag, drop evaporation, and chemical reactions. Also, the interaction between gas phase, liquid phase, turbulence, and chemistry is examined in some detail. Further, a discussion of the boundary conditions is given, in particular, a description of the wall functions used for the simulations of the boundary layers and the heat transfer between the gas and its confining walls. 

Turbulent mixing covers a broad spectrum of applications beyond the field of reactions and reactor design, all of which are affected by the turbulence. Drop breakup, off-bottom solids suspension, gas dispersion, bulk blending, and heat transfer are all affected by the turbulent field. Without a better understanding of this part of the physics, it is difficult to make progress in these areas. With this broader objective clearly in mind, we now move forward to describe the key characteristics of turbulent flow. 

A1 Taweel, A. M., and L. D Walker (1997). Dynamics of drop breakup in turbulent flow, presented at Mixing XIV, 14th Biennial North American Mixing Conference, Williamsburg, VA, June. 

Calabrese, R. V., T. P. K. Chang, and P. T. Dang (1986a). Drop breakup in turbulent stirred-tank contactors 1. Effect of dispersed phase viscosity, AIChE J., 32(4), 657-666. Calabrese, R. V., C. Y. Wang, and N. P. Bryner (1986b). Drop breakup in turbulent stirred-tank contactors lit. Correlations for mean size and drop size distribution, AIChE J., 32(4), 677-681. 

Clark, M. M. (1988). Drop breakup in turbulent flow I. Conceptual and modeling considerations, Chem. Eng. ScL, 43, 671-679. 

Kuriyama M, Ono M, Tokanai H, Konno H (1995) The number of daughter drops formed per breakup of high viscous mother-drop in turbulent flow. J of Chem Eng Japan 28 477 79... 

In many types of contactors, such as stirred tanks, rotary agitated columns, and pulsed columns, mechanical energy is appHed externally in order to reduce the drop si2e far below the values estimated from equations 36 and 37 and thereby increase the rate of mass transfer. The theory of local isotropic turbulence can be appHed to the breakup of a large drop into smaller ones (66), resulting in an expression of the form... 

Atomization. A gas or Hquid may be dispersed into another Hquid by the action of shearing or turbulent impact forces that are present in the flow field. The steady-state drop si2e represents a balance between the fluid forces tending to dismpt the drop and the forces of interfacial tension tending to oppose distortion and breakup. When the flow field is laminar the abiHty to disperse is strongly affected by the ratio of viscosities of the two phases. Dispersion, in the sense of droplet formation, does not occur when the viscosity of the dispersed phase significantly exceeds that of the dispersing medium (13). 

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