Average droplet diameter

When a liquid is dispersed into droplets the surface area is increased, which enhances the rates of heat and mass transfer. For a particular liquid dispersed at constant concentration in air the MIE varies with approximately the cube of surface average droplet diameter, hence the MIE decreases by a factor of about 8 when the surface average diameter D is halved (A-5-1.4.4). Ease of ignition is greatly enhanced for finely divided mists with D less than about 20 /rm, whose MIE approaches that of the vapor. Below 10 /rm a high flash point liquid mist (tetrahydronaphthalene) was found to behave like vapor while above about 40/rm the droplets tended to burn individually [ 142]. Since liquid mists must partially evaporate and mix with air before they ignite, the ease with which a liquid evaporates also affects MIE (Eigure 5-1.4.4). 

Fig. 4.5.17 Plot of average droplet diameter as a function of time at the top of the creamed layer (y/h = 1).

Namely, the average droplet diameter D is roughly twice the liquid jet diameter d(). Another analysis based on the consideration of surface energy gave Xopt= Jtd0 8X ... 

The surface-averaged final diameter Dsf can be easily controlled by adjusting the amount of particles. Because the solid particles are irreversibly adsorbed at the oil-water interface, the inverse average droplet diameter varies linearly with the amount of particles according to the simple equation ... 

Figure 5.12 represents the evolution in time of the surface-averaged droplet diameter for different amounts of solid particles. The kinetic curves confirm the qualitative evolution previously described. The droplet growth is initially rapid but the coalescence rate progressively decreases until the average diameter reaches an asymptotic value. Figure 5.13 shows the change in the droplet size distribution... 

Figure 3.4 Effect of polysaccharide on protein-stabilized emulsions. The diameter ratio, j43nuxtlire / J43protem is plotted against the molar ratio R (moles polysaccharide / moles protein). Here J43nuxtlire is average droplet diameter in fresh emulsion prepared with protein + polysaccharide, and d43pTOtQm is average diameter in emulsion stabilized by protein alone. Key , , legumin + dextmn (48 kDa) or legumin + dextran (500 kDa), respectively (0.5 w/v % protein, 10 vol% oil, pH = 8.0, /= 0.1 M) (Dickinson and Semenova, 1992) O, , asi-casein + pectinate and p-casein + pectinate at pH = 7.0, / = 0.01 M (2.0 w/v % protein, 40 vol% oil), respectively , p-casein + pectinate at pH = 5.5, / = 0.01 M (2.0 w/v % protein, 40 vol% oil) (Semenova et al, 1999). Reproduced from Semenova (2007) with permission.

Figure 6.11 Effect of ionic strength on (a) weight-average molar weight, Mw ( ), and second virial coefficient, A2 ( ), of p-casein in solution at pH = 5.5 and 22 °C, as determined by static light scattering and (b) average droplet diameter, c/43 (A.), and extent of gravity creaming ( ) of p-casein-stabilized emulsion (11 vol% oil, 0.6 wt% protein, pH = 5.5, 22 °C).

Figure 4. Comparison of variations in percentage of fuel evaporated as determined by gas sampling and average droplet diameters (Foster and Ingebo)...

Average droplet diameter, in microns, in standard synthetic rubber formula... 

The nebulizer is normally interfaced directly to the LC column. It combines the eluent with a stream of gas to produce an aerosol. Much of the theoretical and practical basis of nebulization comes from atomic spectroscopy. The average droplet diameter and uniformity of the aerosol are the most important factors for ELSD sensitivity and reproducibility. As larger solute particles scatter light more intensely, an aerosol with large droplets and a narrow droplet size distribution leads to the most precise and sensitive detection. A good nebulizer should produce a uniform aerosol of large droplets with narrow droplet size distribution. The droplets cannot be too large, however otherwise, the solvent in a droplet will not be completely vaporized and errors in detection will occur. The nebulizer properties that can be adjusted to obtain the desired droplet properties are, primarily, the gas flow rate and the LC mobile phase flow rate. ... 

Another type of emulsion-like process is called miniemulsion polymerization. Miniemulsions are stable oil in water emulsions with average droplet diameter of 80-400 nm, prepared using a mixture of an anionic emulsifier and a cosurfactant such as a long-chain fatty alcohol or n-alkane. The polymer latexes are prepared by initiation of polymerization in the miniemulsion droplets. 

The average droplet diameter 32 is obtained from the sum of the volumes of all... 

Figure 10.20 Average droplet diameters obtained in various emulsifying machines as a function of energy consumption (p). Numbers near the curves denote the viscosity...

Transitional inversion can also be induced by changing the HLB number of the surfactant at constant temperature, using surfactant mixtures. This is illustrated in Figure 14.2, which shows the average droplet diameter and rate constant for... 

Alternatively, the average droplet diameter d can be measured as a function of time ... 

Freshly prepared emulsions with various droplet sizes are prepared by controlling the speed of the stirrer used for emulsification. The emulsifier concentration in these experiments should be kept constant, and care taken that there is no excess of emulsifier in the continuous phase. When the viscosity of these freshly prepared emulsions is plotted against the average droplet diameter, a master curve is produced that relates the emulsion viscosity to the average droplet size. The viscosity is seen to decrease monotonicaUy with increases in the average droplet size. 

FIGURE 13.17 Average droplet diameter as a function of time after making of O-W emulsions with various concentrations (numbers near the curves in mg per ml) of amphiphilic peptides. Volume fraction of oil 0.2, pH 6.7, ionic strength 75 mmolar or 150mmolar( ). (Results of P. Smulders et al. Roy. Soc. Chem. Special Public. 227 (1999) 61.)... 

Average droplet diameters are usually in the 10 to 20 tm range. Marine clouds are characterized by relatively smaller droplet concentration and larger diameters, where continental clouds tend to have smaller droplets (Table 15.7). 

For a more accurate determination of the scavenging rate we need to include in our calculations the full droplet spectrum. The simplification of an average droplet diameter can easily lead to significant errors. If the rain droplet size distribution is given by the function n(Dp) (where n Dp) dDp is the number of droplets in the range [Dp, Dp - - dDp]), then the local rate of removal of an irreversibly soluble gas like HNO3 is... 

Spray delivery is more efficient than the other three methods in providing a very fine aerosolization (average droplet diameter = < 5 pm) of agent, which can be inhaled far down into the lungs. This method is particularly suited to the delivery of toxins, which require deep inhalation and which differ from most chemical agents in that they are... 

Figure 14.14 The variation of average droplet diameter, d with mixing time t at various angular speeds, N, when T = 21.5 cm, D = 0.67 T using an inclined paddle and three baffles.

---