Reduction of droplet size

Adapting the evaporative light scattering device (ELSD) to pHPLC was investigated by Gaudin et al. Quantitative analysis by ELSD is often hindered by nonlinearity however, reduction of the flow rate, resulting in better homogeneity of droplet size distribution, has increased the linearity of the response with ELSD. Despite the predictable effect on droplet size in relation to the reduction of the inner diameter of the capillary inside the nebulizer, ELSD is relatively simple to adapt to micro/ capillary EC. ... 

A study on the influence of the viscosity of the dispersed phase in the preparation of emulsions of vegetable oils (olive, soyabean and linseed) in water with US assistance revealed that replacing the oil with the highest viscosity and interfacial tension — olive oil — with soyabean oil, which has slightly lower viscosity and interfacial tension, caused virtually no reduction in droplet size. Linseed oil, with much lower viscosity and interfacial tension than olive oil, exhibited a much smaller Sauter diameter than the latter viz. 0.47 (xm versus 0.62 pm). Breaking low-viscosity droplets requires less vigorous cavitation shock waves than breaking more viscous ones [49]. 

V fV = 49, curve A is obtained. If the mixture of chlorobenzene, water, and emulsifier is treated with a high-speed mixer (Ultraturrax) droplets of chlorobenzene in the micron-size range are formed. When the polystyrene-dioctyladipate particles are added to this dispersion, curve B is obtained. As expected, the reduction in droplet size leads to a substantial increase in the rate of swelling. 

The results of Figure 13 suggest that as the droplet size increases, the emulsion retention increases. The large droplets have a higher capture probability and fill up more of the pores faster, a result that explains why they elute later than the smaller droplets. Emulsions with small droplet size diameters elute with essentially the inlet size distributions. Two factors control permeability reduction the total volume of droplets retained and the effectiveness of these droplets in restricting fiow. For a given porous medium, a critical mean droplet size of the emulsion controls permeability reduction. Below this value, retention of oil in porous media is dominant, and above the critical mean droplet size, their obstruction ability is pronounced. This situation explains the trends shown in Figure 13 for the effect of droplet size on permeability reduction. These conclusions are valid for stable, very dilute OAV emulsions and are based on a few experiments. 

In the absence of any flocculation, the coalescence of an emulsion results in a reduction of its viscosity. At any given volume fraction of oil, an increase in droplet size will result in a reduction of viscosity, and this is particularly the case for concentrated emulsions. Thus, by following the decrease in emulsion viscosity with time, information may be obtained on its coalescence. However, care should be exercised when applying simple viscosity measurements, particularly if flocculation occurs simultaneously (as this results in an increased viscosity). It is possible - at least in principle - to predict the extent of viscosity reduction on storage by combining the results of droplet size analysis (or droplet number) as a function of time with the reduction in viscosity during the first few weeks. 

The reduction of water volumes and the often consequential reduction in droplet sizes required to ensure good coverage of the target. 

The small amounts of aerosol generated by a system such as Halolite are produced over relatively short time period (< 1 s) in a discrete bolus. This bolus is entrained with ambient air during patient inhalation and one would expect a considerable amount of mixing to occur. As ambient air has a significant capacity to absorb water vapor from nebulized aerosol (relative humidity normally <70%), evaporation of aqueous aerosol would be inevitable and rapid. The reduction in droplet size would be expected to be inconsistent, as the rate of evaporation will depend on the speed of inhalation which defines degree of dilution as well as temperature and humidity of ambient air. In contrast, aerosol-laden air inhaled from the Circulaire nebulizer system will entrain little ambient air and is therefore relatively less sensitive to any reduction in droplet size due to evaporation. To what extent evaporation reduces droplet size from Halolite is not known and deserves further investigation. 

Figure 37.3 shows the variations of non-dimensimial droplet diameter squared in the shrinkage period as a function of distance from the reactor inlet for various reactor wall temperatures, for given <1q, Nq, Q, RHq, and Cq. At reactor wall temperature of 200°C, in order for the shrinkage period (period during which no solute is precipitated yet) to terminate, the droplets need to travel 500 mm from the reactor inlet, whereas for the case of the reactor waU temp)erature of 1,000 C, this length is reduced to 50 mm. It is observed that the variation of droplet diameter squared with x (and therefore t) is not linear. In fact, it seems that the rate of droplet size reduction ( evaporation rate) increases with distance from the reactor inlet. 

---