Influence of liquid viscosity

For liquids of higher viscosities, the influence of liquid viscosity on droplet breakup needs to be considered. According to Hinze,[270] the critical Weber number may be modified to the following expression to account for the effect of liquid viscosity ... 

Both effects can produce coarser atomization. However, the influence of liquid viscosity on atomization appears to diminish for high Reynolds or Weber numbers. Liquid surface tension appears to be the only parameter independent of the mode of atomization. Mean droplet size increases with increasing surface tension in twin-fluid atomizers (34). D32 is proportional to CJW, where the exponent n varies between 0.25 and 0.5. At high values of Weber number, however, drop size is nearly proportional to surface tension. 

Stable, P., Gaukel, V., Schuchmann, H. P. (in press). Investigation on the applicability of the effervescent atomizer in spray drying of foods Influence of liquid viscosity on nozzle internal two-phase flow and spray characteristics. Journal of Food Process Engineering, doi 10.1111/ j e.12178. 

The coefficients are defined for infinitely dilute solution of solute in the solvent L. However, they are assumed to be valid even for concentrations of solute of 5 to 10 mol.%. The relationships are available for pure solvent, and could be used for mixture of solvents composed of molecules of close size and shape. They all refer to the solvent viscosity which can be estimated or measured. Pressure has a negligible influence on liquid viscosity, which decreases with temperature. As a consequence, pressure has a weak influence on liquid diffusion coefficient conversely, diffusivity increases significantly with temperature (Table 45.4). For mixtures of liquids, an averaged value for the viscosity should be employed. 

The liquid properties of primary importance are density, viscosity and surface tension. Unfortunately, there is no incontrovertible evidence for the effects of liquid viscosity and surface tension on droplet sizes, and in some cases the effects are conflicting. Gas density is generally considered to be the only thermophysical property of importance for the atomization of liquids in a gaseous medium. Gas density shows different influences in different atomization processes. For example, in a fan spray, or a swirl jet atomization process, an increase in the gas density can generally improve... 

Various correlations for mean droplet size generated by plain-jet, prefilming, and miscellaneous air-blast atomizers using air as atomization gas are listed in Tables 4.7, 4.8, 4.9, and 4.10, respectively. In these correlations, ALR is the mass flow rate ratio of air to liquid, ALR = mAlmL, Dp is the prefilmer diameter, Dh is the hydraulic mean diameter of air exit duct, vr is the kinematic viscosity ratio relative to water, a is the radial distance from cup lip, DL is the diameter of cup at lip, Up is the cup peripheral velocity, Ur is the air to liquid velocity ratio defined as U=UAIUp, Lw is the diameter of wetted periphery between air and liquid streams, Aa is the flow area of atomizing air stream, m is a power index, PA is the pressure of air, and B is a composite numerical factor. The important parameters influencing the mean droplet size include relative velocity between atomization air/gas and liquid, mass flow rate ratio of air to liquid, physical properties of liquid (viscosity, density, surface tension) and air (density), and atomizer geometry as described by nozzle diameter, prefilmer diameter, etc. 

The effects of liquid viscosity on tray efficiency have been studied by Drickamer and Bradford(58) and () Co nt ij. 59- and these are discussed in Section 11.10.5. Surface tension influences operation with sieve trays, in relation both to foaming and to the stability of bubbles. 

Figure 3.21 shows the influence of extensional viscosity on the flow behavior of an aqueous PEO solution. The high extensional viscosity in comparison with the relatively low shear viscosity can cause the upper container to empty when pouring, even when the liquid surface is below the glass rim. This is visible in Fig. 3.21 by the liquid level markings. In the case of the viscous silicone oil however, the liquid thread breaks as the pouring container is tipped back (not shown here). 

Schmitz et al. [89] also reported on the influence of solids on kEa in stirred tanks. Although they applied only one type of solid (glass beads of 88 and 320 pm average diameter) in aqueous solutions, their study is of particular interest because of the wide range in variation of liquid viscosity applied by adding carboxy methylcellulose and by investigating the scale-up aspects by measuring both in a 20 cm and a 45 cm diameter stirred tank. As Schmitz et al. [89] also point out, their result. 

As mentioned earlier, the gas holdup in mechanically agitated contactors has been found to be, apart from geometric parameters, a function of liquid viscosity, surface tension, the electrolytic nature of the solutions, foaming character, etc. Hence, phenomenologically the reduction in power consumption should also depends on these characteristics of the system. Bruijn et al (1974) concluded that the surface tension does not affect the mechanism of cavity formation and its shape to an appreciable extent. However, liquid viscosity influences the stability of the cavity. Hughmark (1980) presented the... 

In addition, the Ohnesorge number describes the influence of the viscosity of the liquid. 

It was not initially obvious that the quartz crystal resonator would operate in liquids, until this was proven experimentally [11,12]. The term associated with the influence of the viscosity, r], and density, p, of liquid in Eq. 1 can be written [13] as ... 

Here d and pf are the thickness and the density of the film. These equations are valid in a particular case, when d < S. The general case for arbitrary df was given in [44]. The first terms in Eqs. 16 and 17 yield the liquid-induced frequency shift and half-width of the resonance in the absence of a film. The terms in brackets describe the influence of fhe viscosity and density of a film of thickness df. According to Eqs. 16 and 17, the ratio of the film-induced halfwidth to the film-induced frequency shift is proportional to d(/S. Thus, for d /S < 1, the contribution of the thin interfacial film to the width is much smaller than its contribution to the frequency shift. For the film acts... 

The physicochemical differentiation of the liquid state from the gaseous and the solid states requires elaborate and formal treatment. But characterization of the liquid state in a fashion useful for lubrication problems can be made much simpler than is required by exact theory. It will suffice for our purposes to begin with the treatment of liquid viscosity in descriptive terms. Then those constitutive and structural aspects of liquids and the liquid state which influence viscosity will be discussed. Similar treatment will be applied to the density and compressibility of liquids. 

When the gas being absorbed is only slightly soluble, the liquid film usually has the controlling resistance because of the high value of m [see Eq. (22.12)], and the corresponding low value of K a leads to a low plate efl5dency [Eq. (21.77)]. The effect of liquid viscosity is also more important when the liquid film controls, because the lower diffusivity in the liquid phase has a more direct influence on... 

In addition to changing the wettability, the influence of liquid parameters such as viscosity ijl or surface tension yiy was explored. Again, the dimensional analysis based on Re and We numbers would discard any dependence of these liquid properties in the large Re and We limits. In contrast, as summarized in Fig. 5, a strong influence of these properties on the threshold value U is exhibited. This suggests furthermore the introduction of a critical capillary number Ca = rji Uly y. One may note that the capillary number Ca is precisely the ratio between the quantifies we were about to neglect ... 

About (b) When deriving the equation for calculating the Hquid hold-up in the turbulent flow range, ReL > 1-10, the losses of energy due to the influence of the viscosity forces on the liquid element in the packing [19,12] are usually neglected. Based on the balance of forces acting on a fluid element at an inclined plate, Buchanan [19] derived Eq. (4-24) ... 

Fig. 39. Influence of the viscosity after different equations for calculating the mjas transfia coefEcient for liquid-side controlled process and after some experimental data.

The experimental constants in Eq. (183) are obtained based on data for the packings presented in Table 26. For determining the influence of the viscosity of the liquid phase, the experiments are performed with pure smter and water solutions of sugar or glycerine. The viscosity is changed fimn 10 to 9.1(T ] s and the density from 1000 to 1160 kg/m. The liquid siqierficial velocity varies from 3.10-3 to 2.10-2 m /(m s). 

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