Maximum droplet pressure method

A variation of this technique, the maximum droplet pressure method, can be used to determine interfacial tensions. This technique is especially useful in situations for which the density contrast between the two liquid phases is very low, or non-existent [144,145],... 

For emulsions, the interfacial tension is usually of most interest. Here, the du Noiiy ring, Wilhelmy plate, drop volume, pendant, or sessile drop methods are the most commonly used. The spinning drop or captive drop techniques are applicable to the very low interfacial tensions encountered in the enhanced oil recovery and microemulsion fields. The maximum droplet pressure technique can be used when there is little or no density contrast between the phases, such as in bitumen-water systems at elevated temperature. 

The third method for measuring dilational elasticity and viscosity is the maximum bubble pressure method (33). Although this method overcomes some of the problems encountered in the surface wave and droplet deformational methods, it can only be applied for measurement at the air/liquid interface. 

Only the two first methods allow measurement of the temperature coefficient of the surface energy. The maximum bubble pressure technique is well-adapted for metals with low and intermediate melting points and specially for oxidizable metals, while the sessile drop technique has been applied with success to measure ctlv values up to 1500°C. The drop weight method is particularly useful for very high melting-point metals because it avoids liquid contact with container materials. This is also true for the recently developed levitation drop technique that analyses the oscillation spectrum of a magnetically levitated droplet. 

A variant is the micro-pipette method, which is also similar to the maximum bubble pressure technique. A drop of the liquid to be studied is drawn by suction into the tip of a micropipette. The inner diameter of the pipette must be smaller than the radius of the drop the minimum suction pressure needed to force the droplet into the capillary can be related to the surface tension of the liquid, using the Young-Laplace equation [1.1.212). This technique can also be used to obtain interfacial tensions, say of individual emulsion droplets. Experimental problems include accounting for the extent of wetting of the inner lumen of the capillary, rate problems because of the time-dependence of surfactant (if any) adsorption on the capillary and, for narrow capillaries accounting for the work needed to bend the interface. Indeed, this method has also been used to measure bending moduli (sec. 1.15). 

For molten silicon, density is measured either by the maximum bubble pressure, sessile drop, levitation, Archimedean or pycnometer method. Mukai and Yuan [14] evaluated density and thermal expansion coefficient of molten silicon precisely. Figure 4.3 shows the principle of the improved sessile drop method, where the volume of a droplet is obtained from its recorded shape. The density, p, is calculated dividing mass M by the volume V, as follows. 

D. C. Raskazov et al. [2.13] used a modified Rankine viscometer with a closed-contour capillary. The distinctive feature of this viscometer was the removal of mercury, which creates the pressure in the capillary, to the region of room temperature and fixing the falling time of the mercury droplets by the noncontact method using high-quality resonance contour. The maximum relative error of experimental data, according to the author s evaluation did not exceed 2-2.3%. The content of impurities in Freon-21 amounted to 0.13%. 

This feattire conducts water and salt removal. The vanes, which are constructed from corrosion-resistant marine grade aluminum (other materials are available), are produced with a profile that allows the maximum removal of salt and water, yet produces an extremely low pressure loss. This optimal profile has been achieved by the very latest design methods, and in particular by utilizing a Computational Fluid Dynamics (CFD) flow modeling system. Hydra also incorporates a unique and novel method of separating water droplets from the air stream, and this has led to improvements in bulk water removal compared with conventional methods. 

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