Weber number mixture

Drops may break up after being entrained in the vapor core. Vapor is generated continuously as a result of heat addition, leading to acceleration of the mixture and increased slip velocity. The sizes of drops formed in this way are characterized by the Weber number based on the slip velocity S. 

As the mixture accelerates, the globs of liquid break up downstream and are exposed to an accelerating vapor flow, with increasing relative velocity between the two phases. This relative velocity further breaks the drop into smaller ones depending on the Weber number,... 

In the case of batch agitation of immiscible liquid mixtures there are relatively few data. Presumably the same curves developed for single liquids could be applied provided the physical properties of the mixture could be adequately characterized. The Weber number Nwe is presumably of importance, since it introduces the property of interfacial tension, but there has been no work establishing its influence. Miller and Mann (M2) found that use of an arithmetic average of the densities of the unmixed liquids,... 

Where W is the Weber number and a.- is the shear stress, the same on both sides of the Interface. The critical condition for drop breakup in Newtonian liquid mixtures is given by ... 

Droplets of heterogeneous composition appear to break faster than single compounds. Figure 6.4 shows a sequence of JP-10 with 5% ethyl-hexyl nitrate. The Mach number ranged from 2.15 to 2.31, and the Weber numbers ranged from 3900 to 5200 based on mixture measured surface tension. 

Orzechowski derived two more correlations, one for kerosene 24.7.x, and the other for a water-glycerin mixture 24.7.xi. The correlations are said to be a functirm of film thickness, Weber number and Ohnesorge s number. The effect of film thickness and Weber number remains unchanged on both liquids. The difference arises in Ohnesorge s number, where the exponent is slightly lower for kerosene. Figure 24.46 shows a comparison of the two equations, using t = 0.1 nun. 

To accelerate the diffusion rate and shorten the time for the formation of gas/polymer solutions, we must raise the temperature and shorten the diffusion distance. This is done by deforming the two-phase mixture of polymer and gas through shear distortion to decrease the diffusion path. This type of deformation occurs in an extruder under laminar-flow conditions. The bubbles are stretched by the shear field of the two-phase mixture and eventually break up to minimize the surface energy when a critical Weber number is reached (4). The disintegrated bubble size is calculated to be about 1 mm and the initial striation thickness after bubble disintegration is calculated to be about twice the bubble diameter (5). This striation thickness decreases with further shear, and the gas diffusion occurs faster as a result of the increase in the surface area and the decrease in striation thickness. The striation thickness in an extruder is estimated to decrease to about 100 /xm. At this thickness, the diffusion time is about 1 min in PET, from 10 to 20 s in polystyrene (PS), polyfvinyl chloride) (PVC), and high density polyethylene (HDPE), and in the range of a few seconds in low density polyethylene (LDPE). 

Fig. 22.5 Dimensionless breakup lengths of liquid threads plotted against the gas-Weber number for two dimensionless flow rates and viscosities. With increasing gas relative velocity, the breakup length decreases. Higher viscous threads show minor decay of breakup length compared to threads with lower viscosity. Increasing flow rate expressed by F leads to longer threads. Test liquids are glycerol water mixtures [33]...

For PVP solution, the mean drop size is comparable to the Newtonian case with a glycerol-water mixture. The drops emerging from silica dispersion are nearly of equal size for the covered gas-Weber number. They are in the same order of magnitude as the prediction specifies in (22.11) [11]. The results were compared with simulations of the drop formation at Institute for Mechanical Process Engineering, University of Stuttgart, Germany [34, 35]. 

Von Weber [170], taking as basis Kuhn s model of a countercurrent system [3] — which consists of two vertical, parallel, plane surfaces — calculated intensity values for the test mixture n-heptane-methylcyclohexane, starting with the maximum number of separating stages (3.54 per cm) and the optimum vapour velocity (0.1525 cm/sec). The figures so obtained are collected in Table 20. 

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