Effect of Viscosity and Surface Tension

Adhesion is defined as the state in which two surfaces are held together by interfacial forces which may consist of valence forces or interlocking action or both [32]. An adhesive is a material capable of holding materials together by surface attachment. Valence forces are not required in order that excellent adhesion be obtained since the van der Waals forces are in themselves sufficient to cause excellent adhesion. 

The early adhesives were natural products (e.g. glues, starch, natural resins) but most modern adhesives are based on synthetic polymers (e.g. polyacrylates). In adhesion, two materials come sufficiently dose for strong interaction to occur. The interface is considered as the zone between the interacting substances, which is sometimes referred to as the interphase. 

The main forces responsible for adhesion are van der Waals, which for convenience are considered to be made of three main contributions Dipole-dipole interaction (Keesom force), dipole-induced-dipole interaction (Debye force) and London dispersion force. A hydrogen-bonding force can also be induded in the interaction. 

For an adhesive joint to be formed, the adhesive must move into the bond area and remain there until the bond is completely established. The rheology of the polymer systems used as adhesives plays a significant part in adhesion. For adhe- 

Electrostatic forces arising from contact or junction potentials between the adhesive layer and the substrate may contribute significantly to the forces required to rupture the bonds. Poor performance results from non-uniform contact or low contact density. 

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Carry out a dimensional analysis and correlate this data in a form that is convenient to use if it is required to predict the bubble diameter for a given system. Represent the effects of viscosity and surface tension so that they each appear in only one group. 

Pa-s (1 to 150 cP) and surface tension over the range of 0.03 to 0.07 N/m (30 to 70 dyn/cm). His equation predicts about an 8 percent increase in flow for a liquid of 0.1-Pa-s (100-cP) viscosity compared with water at 0.001 Pa s (1 cP) and about a 1 percent increase for a liquid with one-half of the surface tension of water. For fluids of moderate viscosity, Ranga Raju and Asawa [Proc. Am. Soc. Civ. Eng., J. Hydraul. Div., 103 (HY 10), 1227-1231 (1977)] find that the effect of viscosity and surface tension on the discharge flow rate for rectangular and triangular-notch ((j) = 45°) weirs can be neglected when... 

The effects of viscosity and surface tension of the solution on the degradation process are not pronounced. Jellinek (44) extended the theory of the collapse of cavitation bubbles, induding the effects of viscosity and surface tension. From his observations it follows that high surface tension accelerates the collapse of the cavities, whereas high viscosity has a retarding effect. According to Okuyama (69), however, increasing viscosity retards only the diffusion of gas molecules from the... 

If the blending process is between two or more fluids with relatively low viscosity such that the blending is not effected by fluid shear rates, then the difference in blend time and circulation between small and large tanks is the only factor involved. However, if the blending involves wide disparities in the density of viscosity and surface tension between the various phases, then a certain level of shear rate may be required before blending can proceed to its ultimate degree of uniformity. 

Air Reiease The air release properties of a dispersion PVC resin are governed by both the formulation and the surface coating on the plastisol resin. Air release is facilitated by low plastisol viscosity at low shear rates and a reduced surface tension. Coatings on the dispersion resin particle siuface can have a significant effect on viscosity and surface tension, as can other additives. Resin particle size can also play a role in air release, with larger particle sizes yielding improved air release. 

Effect of Physical Properties on Drop Size Because of the extreme variety of available geometries, no attempt to encompass this variable is made here. The suggested predictive route starts with air-water droplet size data from the manulac turer at the chosen flow rate. This drop size is then corrected by Eq. (14-195) for different viscosity and surface tension ... 

For many laboratoiy studies, a suitable reactor is a cell with independent agitation of each phase and an undisturbed interface of known area, like the item shown in Fig. 23-29d, Whether a rate process is controlled by a mass-transfer rate or a chemical reaction rate sometimes can be identified by simple parameters. When agitation is sufficient to produce a homogeneous dispersion and the rate varies with further increases of agitation, mass-transfer rates are likely to be significant. The effect of change in temperature is a major criterion-, a rise of 10°C (18°F) normally raises the rate of a chemical reaction by a factor of 2 to 3, but the mass-transfer rate by much less. There may be instances, however, where the combined effect on chemical equilibrium, diffusivity, viscosity, and surface tension also may give a comparable enhancement. 

Solvents influence rate as well as selectivity. The effect on rate can be very great, and a number of factors contribute to it. In closely related solvents, the rate may be directly proportional to the solubility of hydrogen in the solvent, as was shown to be the case for the hydrogenation of cyclohexene over platinum-on-alumina in cyclohexane, methylcyclohexane, and octane 48). Solvents can compete for catalyst sites with the reacting substrates, change viscosity and surface tension (108), and alter hydrogen availability at the catalyst surface. 

W-3 CHF correlation. The insight into CHF mechanism obtained from visual observations and from macroscopic analyses of the individual effect of p, G, and X revealed that the local p-G-X effects are coupled in affecting the flow pattern and thence the CHF. The system pressure determines the saturation temperature and its associated thermal properties. Coupled with local enthalpy, it provides the local subcooling for bubble condensation or the latent heat (Hfg) for bubble formation. The saturation properties (viscosity and surface tension) affect the bubble size, bubble buoyancy, and the local void fraction distribution in a flow pattern. The local enthalpy couples with mass flux at a certain pressure determines the void slip ratio and coolant mixing. They, in turn, affect the bubble-layer thickness in a low-enthalpy bubbly flow or the liquid droplet entrainment in a high-enthalpy annular flow. 

The important liquid phase physicochemical properties which affect the cavitation phenomena and hence the extent of cavitational effects for the given application include vapor pressure, viscosity and surface tension. 

The liquid properties of primary importance are density, viscosity and surface tension. Unfortunately, there is no incontrovertible evidence for the effects of liquid viscosity and surface tension on droplet sizes, and in some cases the effects are conflicting. Gas density is generally considered to be the only thermophysical property of importance for the atomization of liquids in a gaseous medium. Gas density shows different influences in different atomization processes. For example, in a fan spray, or a swirl jet atomization process, an increase in the gas density can generally improve... 

A high proportion of the complex phenomena shown by emnlsions and foams, which are common when petroleum enters the environment, can be traced to these induced surface-tension effects. Dissolved gases, even hydrocarbon gases, lower the surface tension of oils, but the effects are less dramatic and the changes probably result from dilution. The matter is of some importance in environmental issues because the viscosity and surface tension of the petroleum govern the amount of oil that migrates or can be recovered under certain conditions. 

Colloidal potassium has recently been proved as a more active reducer than the metal that has been conventionally powdered by shaking it in hot octane (Luche et al. 1984, Chou and You 1987, Wang et al. 1994). To prepare colloidal potassium, a piece of this metal in dry toluene or xylene under an argon atmosphere is submitted to ultrasonic irradiation at ca. 10°C. A silvery blue color rapidly develops, and in a few minutes the metal disappears. A common cleaning bath (e.g., Sono-clean, 35 kHz) filled with water and crushed ice can be used. A very fine suspension of potassium is thus obtained, which settles very slowly on standing. The same method did not work in THF (Luche et al. 1984). Ultrasonic waves interact with the metal by their cavitational effects. These effects are closely related to the physical constants of the medium, such as vapor pressure, viscosity, and surface tension (Sehgal et al. 1982). All of these factors have to be taken into account when one chooses a metal to be ultrasonically dispersed in a given solvent. 

Although more expensive than melt fiberization, the sol processes offer advantages in fiber chemistry selection. In melt fiberization, viscosity and surface tension are gready influenced by additions of small quantities metallic oxides. In the sol process, where viscosity can be controlled independently, any number of metal salts may be added without adverse effects. These salts can serve as grain growth inhibitors, sintering aids, phase stabilizers, or catalysts. 

Larachi et al. [37] presented a simplified version of Ellman s correlation. A friction factor, fiGG, is represented as a function of dimensionless groups which takes inertia, viscosity and surface-tension effects into account by using, respectively, %g, Rei, and Wee. 

Physical interferences are generally considered to be effects associated with such properties as change in viscosity, and surface tension can cause significant inaccuracies, especially in samples that may contain high dissolved solids, or acid concentrations, or both. If these types of interferences are operative, they must be reduced by dilution of the sample or utilization of standard addition techniques, or both. 

Figure 8. Effect of density, viscosity, and surface tension on droplet size.

The most effective solvents for use in atomic absorption are medium weight, low volatile aliphatics, alcohols and ketones. Frequently used solvents are methyl isobutyl ketone (MIBK) and ethyl propionate. These solvents have viscosities and surface tensions such that the efficiency of nebulisation is increased. 

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