Studying drop size distribution

The range of dispersed-phase velocity studied by Keith and Hixson (K3) is from 10 to 30 cm/sec which, according to those authors, is of industrial interest. The results obtained by them in the absence of mass transfer can be predicted roughly by extrapolation of the Hayworth and Treybal correlation. In the presence of mass transfer, the results obtained (F2), the drop size distribution, flooding, etc. are different from those observed in the absence of mass transfer. There is no reliable theory at present which can predict the drop size distribution in sprays, though rough approximations are possible when mass transfer is completely avoided. 

Computer programs accounted for the presence of oil drops below- the detection limit of the Coulter Counter. The data processing procedure, which assumed that the oil-drop size distribution was lognormal, yielded accurate estimates of the true mean and standard deviation describing the emulsion drop size distribution. The data-analysis procedure did not affect the actual measured drop populations which were used in the kinetic studies. The computer programs are described in detail by Bycscda.8... 

Experiments were conducted varying the residence time, air flowrate, and oil concentration over the same ranges used to study overall system performance. The oil concentrations and drop-size distributions were measured at the entrance and exit of each stage. Table 2 shows typical results. Most of the drop removal for the large drops and production of the small drops occurred in the first stage. The third notation cell had the lowest rates of drop production and aggregation and the largest drops which were least influenced by these effects. Thus, this portion of the data was analyzed to determine the order of the kinetic process for drop removal by air bubbles. A typical plot of the oil removal rate vs. the outlet oil concentration is shown in Fig. 4 the oil removal process is first-order with respect to the concentration of oil drops. 

I he experimental determination of drop-size distributions of fuel sprays is important for all studies involving the atomization of liquid fuels. Investigations of the mechanism of atomization, influences of the many factors that determine fineness of the spray, and methods of atomization and nozzle design all require some means for determining the extent to which the liquid is broken up into droplets in preparation for combustion. 

This paper discusses preliminary results of a model which is designed to predict drift deposition drop size distributions and number flux. The influence of evaporation and the drop breakaway process are studied by using both a bulk breakaway criteria and a distributed partial breakaway criteria for each drop size. Comparisons are made at several downwind receptor sites for drop size distribution and number flux. 13 refs, cited. 

Other studies were conducted by the FS in 1976 to expand the data base on the size of drops which deposited on Douglas-fir needles. These studies provided an opportunity to determine if the drop size distribution would be similar to drop size distributions of tank mixes studied earlier. The 1976 study involved aerial application of acephate and trichlorfon, and the 1981 study involved Bacillus thuringiensis (Dipel 4L and Thuricide 16B). These data have not been published or reported previously. The chemical tank mixes were applied by helicopter and the B.t. tank mixes were applied by fixed-wing aircraft. 

The B.t. drop stain sizes from the 1981 study were assessed in a similar manner as the chemical tank mixes. Results (Table X) differed, however, from the 1976 chemical applications. Sixty percent of the Dipel 4L drop stains were less than 42 pm in diameter and 42 percent of the Thuricide 16B drop stains were less than 31 pm in diameter. Differences between the chemical and biological spray drop size distribution, however, may be due to variation in spreading of the drop after it deposits on the needle. There was no statistical difference in percent distribution of the drop stain sizes between the two B.t. tank mixes or between the two chemical tank mixes. 

The effect of coalescence and break-up of droplets on the yield of chemical reactions was studied by Villermaux (33). Micromixing effects may occur even in batch reactors if there is a drop size distribution and mass-transfer control. Although practical rules for the design and scale-up of liquid-liquid reactors are available as Oldshue showed in the case of alkylation (152), many problems remain unsolved (.5) mass transfer effects, high hold-up fractions (> 20 %), large density differences, high viscosities, influence of surfactants. 

Reaction of dissolved gases in clouds occurs by the sequence gas-phase diffusion, interfacial mass transport, and concurrent aqueous-phase diffusion and reaction. Information required for evaluation of rates of such reactions includes fundamental data such as equilibrium constants, gas solubilities, kinetic rate laws, including dependence on pH and catalysts or inhibitors, diffusion coefficients, and mass-accommodation coefficients, and situational data such as pH and concentrations of reagents and other species influencing reaction rates, liquid-water content, drop size distribution, insolation, temperature, etc. Rate evaluations indicate that aqueous-phase oxidation of S(IV) by H2O2 and O3 can be important for representative conditions. No important aqueous-phase reactions of nitrogen species have been identified. Examination of microscale mass-transport rates indicates that mass transport only rarely limits the rate of in-cloud reaction for representative conditions. Field measurements and studies of reaction kinetics in authentic precipitation samples are consistent with rate evaluations. 

Very few studies have been conducted so far to determine the transient drop size distributions used to elucidate the dynamic processes related with breakage and coalescence of the dispersed phase. Bajpai et al. [92] proposed a method for the measurement of the unsteady-state drop size distributions by... 

Another possibility could be the atomization of emulsions (simple or double) with a twin-fluid nozzle, in cold atmosphere such as -30°C, to produce solid particles. This process is used to study the atomization process (drops size distribution, shape) through the microstructure of the solid particles. 

The rheological parameters of primary scientific and practical concern are the static and dynamic shear modulus, the yield stress, and the shear rate-dependent viscosity. The aim is to understand and predict how these depend on the system parameters. In order to accomplish this with any hope of success, there are two areas that need to be emphasized. First, the systems studied must be characterized as accurately as possible in terms of the volume fraction of the dispersed phase, the mean drop size and drop size distribution, the interfacial tension, and the two bulk-phase viscosities. Second, the rheological evaluation must be carried out as reliably as possible. 

Babinsky and Sojka [23] used DPF to study non-Newtonian liquid drop size distributions. For a single fluctuation, their results showed that fluctuations in ALR and interphase velocity slip ratio have the largest effect on effervescent atomizer/q. For two simultaneously fluctuating quantities, the influence on/o is found by adding... 

Several studies of the drop size distribution and axial mixing have also been reported for the Yoth-Scheibel column. The more recent designs " are reported to give even higher efficiencies. Commercial columns with diameters up to 2.59 m (8.5 ft) have been operated successfully. 

In this chaptCT we focus our attention on key optical methods and nuclear magnetic resonance (NMR), which have been indispensable for quantitative descriptions of size and structure, and diffusivity, where size and structure play an important role. Whereas in the previous chapters we have tended to focus on the overall dynamics, we concentrate here at the smallest scale needed to understand what the fundammtal building blocks are in those systems. With the exception of NMR, the other methods are restricted to transparent systems. This can sometimes be a drawback, as in the study of water-in-crude oil emulsions, which are black in color. These are very important systems industrially and require de-emulsification. NMR techniques for measurement of drop size distributions in such emulsions, while beyond the scope of this chapter, have been reviewed by Pena and Hirasaki (2003). 

There have been a few studies of drop size distributions, and they appear to be similar. Calabrese et al. (1988) give... 

In the following study an extensive investigation is done by the atomization of PVPs with a shear viscosity range from 1 to circa 70 mPa s. The variation is done with PVP K17, K30 and K90 at two different gas velocities, four different liquid mass flows and each with six different mass fractions. The resulting 144 drop size distributions (DSD) are also measured by laser diffraction, with a minimum number of six repetitions and with the same twin-fluid nozzle as before. The motivation was to get a detail understanding of the influence of ALR, mass fraction and viscosity on the drop formation. 

The preceding section provides us with a technique for estimating the volume-averaged drop size of a collection of droplets flowing within a pipe under mist-annular flow conditions. And while this is often all that one may wish to know about the droplet distribution, it is sometimes of interest to know, or at least estimate, the entire drop size distribution. Such would be the case if one wished to perform a cyclone simulation study which required, as input, an estimate of the inlet drop size distribution which may exist within the upstream pipe feeding the cyclone. 

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