Droplet size measurement counters

Figure 6 Oil droplet size distribution of on olive oil emulsion, stabilized with hydroxy-propyl mcthylceUkiloae, after different emulsification procedures blender (triangles), ultrasonic probe (squares), and ultrasonic homogenize (stars). Theoretical distributions were calculated from Coulter Counter measurements using a software program, assuming spherical particles.

A fourth way is to count droplets individually. First, one has to dilute the emulsion strongly. Then, this diluted emulsion is pushed through a small hole. At the same time, the electrical conductivity through the hole is measured. Every time an emulsion droplet moves through the hole, the droplet will obscure part of the hole, which suddenly reduces the conductivity through the hole— the larger the droplet is, the stronger is the effect. Also in this way a droplet size distribution can be obtained. This method is usually referred to as the Coulter counter method, after an important manufacturer of this type of equipment. 

Measurement of the PIT can at best be used as a guide for the preparation of stable emulsions. Any assessments of stability should be evaluated by following the droplet size distribution as a function of time, using a Coulter counter or... 

The break-up of Newtonian liquids with various viscosities t] can be investigated by mastication of small oil samples and measuring the resulting droplet size distribution, using a Coulter Counter or a Master sizer. Samples are expectorated into a suitable surfactant solution, e.g. Tween (to prevent coalescence during measurements). can be measured at 37 °C (body temperature) using a suitable rheome-... 

An acoustical particle counter for counting and sizing fog droplets has been evaluated by Singh and Reist.161 Fog droplets, mostly in the size range of 5-30 pm, were measured by the acoustical particle counter as well as an optical and an electron microscope for comparison. The mean droplet diameters estimated from the acoustical particle counter were in agreement with the microscope values. A Rich 100 condensation nuclei monitor was also operated simultaneously during the fog droplet counting to monitor condensation nuclei counts. 

Several commercially available devices can be employed at the outlet of the separation system. The use of an optical drop counter is advantageous if aqueous solvents are used as eluents. With respect to usually very low concentrations of separated substances in the eluate, the surface tension and the size of the droplets are usually not affected. A siphon equipped with a photo-optical sensor may also be used to measure the retention volume. If water is used as the eluent, there are problems with the drops adhering to the inner siphon surface. 

Hess, C. F., Non-intrusive optical single-particle counter for measuring the size and velocity of droplets in a spray, Applied Optics, 23, 4375-4382 (1984)... 

The CCN behavior of ambient particles can be measured by drawing an air sample into an instrument in which the particles are subjected to a known supersaturation, a so-called CCN counter (Nenes et al. 2001). If the size distribution and chemical composition of the ambient particles are simultaneously measured, then the measured CCN behavior can be compared to that predicted by Kohler theory on the basis of their size and composition. Such a comparison can be termed a CCN closure, that is, an assessment of the extent to which measured CCN activation can be predicted theoretically [see, for example, VanReken et al. (2003), Ghan et al. (2006), and Rissman et al. (2006)]. The next level of evaluation is an aerosol-cloud drop closure, in which a cloud parcel model, which predicts cloud drop concentration using observed ambient aerosol concentration, size distribution, cloud updraft velocity, and thermodynamic state, is evaluated against direct airborne measurements of cloud droplet number concentration as a function of altitude above cloud base. The predicted activation behavior can also be evaluated by independent measurements by a CCN instrument on board the aircraft. Such an aerosol-cloud drop closure was carried out by Conant et al. (2004) for warm cumulus clouds in Florida. 

One of the promising methods for producing satisfied quantities of a powder with narrow size distribution and nanometric mean diameter is electrospray pyrolysis method. In this method, a meniscus of a precursor (spray solution) at the end of capillary tube becomes conical when charged to a high voltage (several kilovolts) with respect to a counter electrode. The droplets are formed by continuous breakup of a jet extending from this liquid cone, known as Taylor cone. Lenggaro, Xia, Okuyama, and Fernandez de la Mora, in their papers published from 2000 to 2003, described how this technique functions and how it is possible to measure online a size distribution of particles obtained from different types of precursor systems. For this purpose, they used differential mobihty analyzer and a condensation nucleus/particle counter (CNC/ CPC) [19-26]. 

Emulsions are visually checked for homogeneity and evenness. They should not contain large droplets and no phase separation should occur. The drop size of emulsions can eventually be measured with particle counters, see Sect. 35.9.3. 

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