Typical Values of Viscosity

1 Liquids. The viscosity of different liquids varies widely.8 Their viscosity decreases with increasing temperature. Generally, liquid viscosity is very sensitive to temperature. For non-polar and non-associating liquids, viscosity follows Arrhenius type behaviour, p = p0 exp(—EfRT). 

Typical values of viscosities of liquids and gases are given in Table 1. It can be seen that viscosities of liquids vary widely over many orders of magnitude. 

3 Gases. At moderate pressures, gas viscosity increases with increasing temperature, p oc T0 7-10, and is relatively independent of pressure. 

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Table 4.1 presents typical values of viscosities of some common materials. One can see from this table that viscosity varies over several orders of magnitude. One may also note that, although the table lists a viscosity for glasses, the magnitude of the viscosity clearly suggests that the deformation of glasses at room temperatures will be extremely small so glasses are best treated as solids under normal conditions. (Recall the discussion in Section 4.1c of time scales and their relation to whether a substance is defined as a liquid or a solid.) Typical rates of shear for some familiar processes are shown in Table 4.2. 

Table 1 Typical values of viscosity of some gases and liquids at 20°C, 1 atm...

Table 3.2 shows a comparison of typical values of viscosity. At the molecular level, in order to move part of a polymer molecule, there has to be a hole available to accommodate it. The viscosity of a solutiou is therefore increased when the required holes can form with difficulty. Viscosity is increased by increasing the viscosity of the solvent, or by increasing the polymer concentration or the molecular weight of the polymer (Figure 3.6). Solveuts vary considerably in viscosity, and their viscosity is reduced considerably with increased temperature. 

With typical values of = 6 x 10 N s/m and b = 0.01 s, penetration will be about ten diameters under a driving pressure of 1 N/mm- (ca. 10 atmospheres). With a higher initial viscosity of 6 x 10 N s/m — perhaps as a result of delay in applying the same adhesive — penetration would only be 3.2 diameters. 

The kinematic viscosity v is of more fundamental importance than the dynamic viscosity fi and it is appropriate to consider typical values of both these quantities, as shown in Table 1.2. 

Keeping in mind the typical values of tv and [Pg.120]

Table 1. Typical values of densities p, viscosities q and diffusion coefficients D for different fluids [1], where Tcrit and pcrit are the critical temperature and pressure.

The rates of ion separation from CIP to SSIP are apparently much less structure dependent. Again the solvent polarity plays the dominant role. The typical values of ksep vary from ca. 5 x 108 s 1 in acetonitrile to about 105 s 1 in dichloromethane [50b, 122,123]. The empirical Weller equation [123] (Eq. 8, where rj is the solvent viscosity in cPs-1, r is the ion separation distance within the pair and d = oo) accounts well for the ion dynamics. 

Interestingly, the diffusional behavior of membrane proteins measured experimentally by FRAP, FCS, or single particle tracking in cells is more complex than predicted by this model. This technique is described best for the case of cell surface proteins, as assessed by FRAP. Such measurements indicate that diffusion is typically much slower than one would expect based on membrane viscosity. In cell membranes, typical values of D for transmembrane proteins are approximately 0.05 pm /s or less, which is much slower than observed in artificial membranes composed of purified lipids. In addition, a significant fraction of proteins is often immobile over the timescale of diffusion experiments (4, 5). Furthermore, diffusional mobilities vary among proteins, and sometimes they differ for the same protein expressed in different cell lines (4, 5). Deviations from pure diffusion are more readily apparent when the trajectories... 

Our objective here is to try to answer the following questions For a proposed type of gas-liquid contactor compatible with the properties and flow rates of the phases and with the reaction type, what are the likely values of the specific interfacial area and the gas and liquid mass-transfer coefficients by which the contact performance can be predicted And what is the expected accuracy of these values Table XVIII gives typical values of these parameters in typical contactors shown in Fig. 12 for fluids with properties not very different from those of air and water (especially, liquid viscosity under 5 cP where the liquid is nonfoaming). Because this review is especially concerned with the chemical method of determining these parameters, experimental data obtained by this method will be given in subsequent tables and figures. 

When the film thickness h is sufficiently large, one observes the rheological behavior typical of bulk fluids [201,202]. Flow can be described by the bulk viscosity pg and a shp length 5 at each wall. As in simulations, typical values of S are comparable to molecular dimensions and would be irrelevant at the macroscopic scale. However, a few systems show extremely large slip lengths, particularly at high shear rates [203,204]. 

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