Triggers, 14 viscosity

The preparation has a viscosity of approximately 0.67 Pascal seconds and a triggered viscosity ratio at a 50% dilution with water of 10.5. If using alternate vehicle composition (above), the preparation has a viscosity of approximately... 

Unlike at adiabatic conditions, the height of the liquid level in a heated capillary tube depends not only on cr, r, pl and 6, but also on the viscosities and thermal conductivities of the two phases, the wall heat flux and the heat loss at the inlet. The latter affects the rate of liquid evaporation and hydraulic resistance of the capillary tube. The process becomes much more complicated when the flow undergoes small perturbations triggering unsteady flow of both phases. The rising velocity, pressure and temperature fluctuations are the cause for oscillations of the position of the meniscus, its shape and, accordingly, the fluctuations of the capillary pressure. Under constant wall temperature, the velocity and temperature fluctuations promote oscillations of the wall heat flux. 

Generally, a phase transition is triggered by an external stress which most commonly is a change in temperature or pressure. Properties that can change discontinuously include volume, density, specific heat, elasticity, compressibility, viscosity, color, electric conductivity, magnetism and solubility. As a rule, albeit not always, phase transitions involve structural changes. Therefore, a phase transition in the solid state normally involves a change from one to another modification. 

A loss in viscosity occurs when enzymes, organic catalysts manufactured by bacteria and/or fungi, start to destroy the thickener. These enzymes are capable of triggering reactions quickly and for indefinite periods. One enzyme molecule can effectively change millions of raw material molecules to undesirable end products. The result can be a paint or coating that loses its elastic and elonga-tional properties. 

In the seventies, the growing interest in global geochemical cycles and in the fate of man-made pollutants in the environment triggered numerous studies of air-water exchange in natural systems, especially between the ocean and the atmosphere. In micrometeorology the study of heat and momentum transfer at water surfaces led to the development of detailed models of the structure of turbulence and momentum transfer close to the interface. The best-known outcome of these efforts, Deacon s (1977) boundary layer model, is similar to Whitman s film model. Yet, Deacon replaced the step-like drop in diffusivity (see Fig. 19.8a) by a continuous profile as shown in Fig. 19.8 b. As a result the transfer velocity loses the simple form of Eq. 19-4. Since the turbulence structure close to the interface also depends on the viscosity of the fluid, the model becomes more complex but also more powerful (see below). 

Cellulose acetate phthalate forms a pH-triggered phase transition system, which shows a very low viscosity up to pH 5. This system will coacervate in contact with the tear fluid (pH 7.4), forming a gel in few seconds and releasing the active ingredients over a prolonged period of time. The half-life of residence on the rabbit corneal surface was approximately 400 seconds compared to 40 seconds for saline. However, such systems are characterized by a high polymer concentration, and the low pH of the instilled solution may cause discomfort to the patient. 

Choi et al. proposed to use pH change as a trigger for a poly(acryUc acid) solution because it exhibits a low viscosity at low pH, but at high pH above a critical value, the viscosity increases drastically and maintains more or less a plateau value with further increases in pH, as shown in Figure 5.10. Through injection of a polyelectrolyte at low pH, a low viscosity and good injectivity can be achieved. Once deep in the reservoir, the pH of water can increase because of reaction of injected acid with the carbonate and other minerals in the reservoir rock (and to a certain extent, becanse of mixing between injected... 

Hypochlorite hard surface and drain cleaner compositions exhibiting enhanced extensional viscosity are mentioned in U.S. Patents 5,728,665 and 5,916,859. The viscoelastic compositions are intended for use with trigger sprayers and the hexa-decyl amineoxide/organic counterion compositions provide low bleach odor and reduced spray misting. The patent contains extensional viscosity data in support of the claims. Viscosity as a function of shear rate at various Cm diphenyloxide disulfonate concentrations is shown in Figure 4.5. Examples of steady shear and extensional viscosity as a function of shear rate and extensional rate are shown in Figure 4.6 and Figure 4.7. 

Adam W, Bronstein I, Trofimov AV, VasiTev RE. Solvent-cage effect (viscosity dependence) as a diagnostic probe for the mechanism of the intramolecular chemically initiated electron-exchange luminescence (CIEEL) triggered from a spiroadamantyl-substituted dioxetane. J Am Chem Soc 1999 121 958-61. 

A method for coating microchannel walls with layers as thick as 25 pm was developed by Stefanescu et al. [181]. The microreactor was built from FeCrAl (Aluchrom ). The metal surface was first chemically treated in several steps and afterward annealed at 1200 °C for 1 h to trigger the segregation of aluminum and the formation of an alumina layer on the metallic surface. An alumina washcoat was subsequently deposited from a slurry onto the microstructure and characterized by various physical methods. The authors varied the properties such as viscosity, particle size, and pH of the slurry. Acrylic acid, a component used as dispersant and binder, was found to be particularly important for the adhesion of the alumina layer. 

Identify hazardous chemicals from databases as discussed in Section 16.4.4 and from local legal regulations. Identify the potential for hazards from the checklist for reactivity (in Section 16.4.4) and from HAZOP-type studies or fault-tree analysis (Crowl and Louvar, 1990). In HAZOP studies, use checklist key words as triggers to systematically analyze the impact of changes to flow rate, temperature, pressure, composition, level, viscosity, heat transfer, reaction, and conditions and the potential for barrier failure and startup and shutdown to cause hazards. 

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