Coalescence factor, measurement

Figure 12.6 Influence of the metal coalescence factor = 1 - Achem/Acaic in PtRu/Sibunit catalysts on the CO stripping peak (top) and the specific current for 0.1M methanol oxidation at 0.4 V after 1800 seconds (bottom). Achem is the specific surface area of Pt-Ru particles determined with CO chemisorption, and Acaic is the specific surface area calculated either from the results of XRD (filled symbols) or from TEM (open symbols). The measurements were performed in O.IM H2SO4 at 323 K, BET surface area of Sibunit carbon 72m /g. (From ref. 178, with permission from the Royal Society of Chemistry.)...

As discussed in connection with measuring the coalescence factor it seems anomalous that the very low mechanical strength of the dried product is accounted for by the fact that the wet gel was strengthened so as to shrink less during drying. 

Possible measurement bias factors such as droplet deposition in the probe, droplet breakup and coalescence were studied. A simple criterion for minimizing measurement bias was proposed. The system can be used for both water and liquid-metal droplets. 

Coefficients k, a and b depend on the reactor design. Us is the surface velocity of the gas, Pd is the power consumption and V is the liquid volume. It is observed that the volumetric mass-transfer coefficient for a non-coalescing medium is higher by about a factor of 2 than that measured for a coalescing medium under the same operating conditions. Fermentation media are in general non-coalescent, but biotransformation media, even very simple ones, can be coalescent. 

In salt solutions or mixtures of miscible liquids, the coalescence of tiny primary gas bubbles is suppressed significantly the higher the concentration of the solution, the better the size of the primary gas bubbles is preserved. The stable bubble size in this case is 0.2-0.5 mm, an order of magnitude smaller than in pure liquids. As a result of coalescence suppression, the enhancement factor of physical sorption m = (kLa)sol/(kLa)soly rises to 7 or 8, which has been confirmed by measurements of kLaL as a function of the concentration of various inorganic salts (both strong and weak electrolytes) as well as normal aliphatic alcohols (methanol to octanol) (Zlokarnik, 1980,1985). 

The present paper deals with kinetics of coagulation of Phthallylsulfathiazole stabilized xylene in water emulsion in the presence of some cationic detergents. Rate of flocculation, rate of coalescence and rate of creaming have been determined. To estimate the stability of the present systems their zeta potentials have been measured and stability factors calculated. Temperature effect on the system was also studied. 

Aerosol-sized contaminants are much more difficult to control than particulates because they do not readily settle out of a gas stream. The separation of the aerosol fraction of nongaseous air pollutants may be greatly improved if they are agglomerated (coagulated or coalesced) to the larger particles or droplets before removal is attempted. There are four primary means by which this may be achieved. Awareness of these contributing factors can suggest measures which could be taken to accelerate the process, or make it more efficient. 

The gas-liquid mass transfer factor kiO for standard geometries has been extensively measured and correlated for air-water (coalescing) and air-electrolyte (non-coalescing) solutions. The most successful correlations are of the form... 

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