Viscosity, bulk

Bulk viscosity refers to the ability to generate a pressure, A/ , resistant to a change in volume of a liquid  

Bulk viscosity, rj, is evaluated from the ultrasonic absorption coefficient a and shear viscosity ri by  

The bulk viscosities of molten alkali nitrates measured by Ejima s group 140 are shown in Fig. 27, where the bulk viscosity decreases with increasing temperature. The ratios of /r are approximately constant over the temperature range investigated. This suggests that the activation energies of the bulk viscosity and the shear viscosity are much the same. 

A linear relation exists between the sound-absorption coefficients in the melts and their volumes V, cm ) as a function of temperature  

These equations may be used by interpolation to estimate, with -10% error, sound absorption in melts. 

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While bulk viscosity is a relatively obscure property of a liquid or a solid... 

Templeton obtained data of the following type for the rate of displacement of water in a 30-/im capillary by oil (n-cetane) (the capillary having previously been wet by water). The capillary was 10 cm long, and the driving pressure was 45 cm of water. When the meniscus was 2 cm from the oil end of the capillary, the velocity of motion of the meniscus was 3.6 x 10 cm/sec, and when the meniscus was 8 cm from the oil end, its velocity was 1 x 10 cm/sec. Water wet the capillary, and the water-oil interfacial tension was 30 dyn/cm. Calculate the apparent viscosities of the oil and the water. Assuming that both come out to be 0.9 of the actual bulk viscosities, calculate the thickness of the stagnant annular film of liquid in the capillary. 

Before we are in a position to discuss the viscosity of polymer melts, we must first give a quantitative definition of what is meant by viscosity and then say something about how this property is measured. This will not be our only exposure to experimental viscosity in this volume—other methods for determining bulk viscosity will be taken up in the next chapter and the viscosity of solutions will be discussed in Chap. 9—so the discussion of viscometry will only be introductory. Throughout we shall be concerned with constant temperature experiments conducted under nonturbulent flow conditions. 

The bulk viscosity of polystyrene (M = 371,000) at 200°C was measured by Graessley and Segalt at different rates of shear. At low rates of shear Tjj = 330,000 P and drops off with 7 approximately as follows ... 

Bulk separations Bulk sweeteners Bulk viscosity Bulletproof vests Bullet-resistant glass Bullets... 

Extensional Viscosity. In addition to the shear viscosity Tj, two other rheological constants can be defined for fluids the bulk viscosity, iC, and the extensional or elongational viscosity, Tj (34,49,100—107). The bulk viscosity relates the hydrostatic pressure to the rate of deformation of volume, whereas the extensional viscosity relates the tensile stress to the rate of extensional deformation of the fluid. Extensional viscosity is important in a number of industrial processes and problems (34,100,108—110). Shear properties alone are insufficient for the characterization of many fluids, particularly polymer melts (101,107,111,112). 

For higher molecular weight polydimethyl siloxanes (Af > 2500), the number-average molecular weight is related to the bulk viscosity by the foUowiag formula, where the viscosity units are mm /s(=cSt). 

AH these mechanisms except high bulk viscosity require a stabilizer in the surface layers of foam films. Accordingly, most theories of antifoaming are based on the replacement or modification of these surface-active stabilizers. This requires defoamers to be yet more surface active most antifoam oils have surface tensions in the 20 to 30 mN/m range whereas most organic surfactant solutions and other aqueous foaming media have surface tensions between 30 and 50 mN/m(= dyn/cm). This is illustrated in Table 3. 

The bulk viscosity at 2ero shear rate T q also depends on mol wt (81) ... 

The uncured property most often used for CSM in dry appHcations is Mooney viscosity, alow shear bulk viscosity (ca 1.6 ) determined at 100°C. 

The bulk viscosity control parameter for CSM, as with other elastomers, is molecular weight M and molecular-weight distribution (MWD). Mooney viscosity for CSM is determined by selection of the polyethylene precursor. 

The identity tensor by is zero for i J and unity for i =J. The coefficient X is a material property related to the bulk viscosity, K = X + 2 l/3. There is considerable uncertainty about the value of K. Traditionally, Stokes hypothesis, K = 0, has been invoked, but the vahdity of this hypothesis is doubtful (Slattery, ibid.). For incompressible flow, the value of bulk viscosity is immaterial as Eq. (6-23) reduces to... 

Phase III in Fig. 5 is marked by a cooling of the bond line, which causes the bulk viscosity of the adhesive to rise. During phase IV, another sharp increase in viscosity is observed. This is caused by the re-crystallization of the polymer... 

Experimental measurements of viscosity almost always are recommended when dealing with slurries and extrapolations should be made with caution. Most theoretically based expressions for liquid viscosity are not appropriate for practical calculations or require actual measurements to evaluate constants. For nonclustering particles, a reasonable correlation may be based on the ratio of the effective bulk viscosity, /ig, to the viscosity of the liquid. This ratio is expressed as a function of the volume fraction of liquid x in the slurry for a reasonable range of compositions ... 

Figure 5-37 presents a typical heating and cooling chart for the changes in process side film coefficients, hg, as a function of bulk viscosity for organic chemicals. 

D = impeller diameter, ft N = impeller speed, rpm p = density, Ib/cu ft ft = bulk viscosity of fluid... 

From the weak dependence of ef on the surrounding medium viscosity, it was proposed that the activation energy for bond scission proceeds from the intramolecular friction between polymer segments rather than from the polymer-solvent interactions. Instead of the bulk viscosity, the rate of chain scission is now related to the internal viscosity of the molecular coil which is strain rate dependent and could reach a much higher value than r s during a fast transient deformation (Eqs. 17 and 18). This representation is similar to the large loops internal viscosity model proposed by de Gennes [38]. It fails, however, to predict the independence of the scission yield on solvent quality (if this proves to be correct). 

The relationship between film thickness of hexadecane with the addition of cholesteryl LCs and rolling speed under different pressures is shown in Fig. 25 [50], where the straight line is the theoretic film thickness calculated from the Hamrock-Dowson formula based on the bulk viscosity under the pressure of 0.174 GPa. It can be seen that for all lubricants, when speed is high, it is in the EHL regime and a speed index 4> about 0.67 is produced. When the rolling speed decreases and the film thickness falls to about 30 nm, the static adsorption film and ordered fluid film cannot be negligible, and the gradient reduces to less than 0.67 and the transition from EHL to TFL occurs. For pure hexadecane, due to the weak interaction between hexadecane molecules and metal surfaces, the static and ordered films are very thin. EHL... 

The relationship between the isoviscosity rj and the him thickness is shown in Fig. 28 in which is calculated according to Eq (5) from the experimental data as shown in Fig. 25. When the him is thicker than 25 nm, the isoviscosities of hexadecane with or without LC remain a constant that is approximately equal to the bulk viscosity. As the him becomes thinner, their isoviscosities increase at different extents for different additives. When the him thickness is about 7 nm, the isoviscosity of pure hexadecane is about two times its bulk viscosity, about three times for CP, four times for CA, six times for CAL, and more than ten times for CB. Thus, it can be concluded that the addition of a polar compound into base oil is a beneht to the formation of thicker solid-like layer. 

Figure 22 shows variation of the him thickness with velocities. The three curves in the hgure are results from the EHL solution, experimental data, and TFL solution, respectively. The maximum Hertzian contact pressure is 0.125 GPa and the atmosphere viscosity of oil is 0.062 Pa s. While the velocity is higher than 100 mm s, i.e., the him is thicker than 50 nm, all the results from EHL, TFL, and experimental data are very close to each other, which indicate that when in the EHL lubrication regime, bulk viscosity plays the main role and the results of three types are close to each other. When... 

XlylmnkT/ird ), or h = [TT[i 2RTI2p), as long as substituting the gap-dependent viscosity rather than the bulk viscosity. Because the effective viscosity decreases as the Knudsen number enters the slip flow and transition flow ranges, and thus the mean free path becomes smaller as discussed by Morris [20] on the dependence of slip length on the Knudsen number. 

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