Viscosity variation with temperatur

At the saturation pressure, the viscosity variation with temperature follows a law analogous to that of Clapeyron for the vapor pressure f ) ... 

Although the viscosity index is useful for characterizing petroleum oils, other viscosity—temperature parameters are employed periodically. Viscosity temperature coefficients (VTCs) give the fractional drop in viscosity as temperature increases from 40 to 100°C and is useful in characterizing behavior of siHcones and some other synthetics. With petroleum base stocks, VTC tends to remain constant as increasing amounts of VI improvers are added. Constant B in equation 9, the slope of the line on the ASTM viscosity—temperature chart, also describes viscosity variation with temperature. 

An additive, such as a polymer, that reduces a fluid s viscosity variations with temperature. 

A different approach was made by Dyre et al. (1996) to account for the experimental viscosity variations with temperature as an alternative to VTF and AG models. They considered the flow in viscous liquids to arise from sudden events involving motion and reorganization of several molecules. From the viewpoint of mechanism, the energy required for such flow is minimized if the surrounding liquid is shoved aside to create the necessary volume for rearrangement. This volume is fundamentally different from the volume of the free volume theory and is, in principle, an activation volume. The free energy involved may be written as... 

As developed by Dean and Davis, this empirical method expresses viscosity variation with temperature numerically, initially on a simple scale of 0 to 100, based on two sets of reference distillate fractions. These oils were from two crudes whose distillates had not been refined in any manner (i.e., they had not been dewaxed or solvent refined). The viscosity changes with temperature of the 0 reference oil fractions were large, while those of the fractions from the 100 reference were small. These assignments of 0 and 100 were of course arbitrary and reflected experience at that time. It was assumed in developing the method that all distillation fractions from each of these reference crudes had the same VI (and that approximately agreed with the current knowledge) and that this was true for all other crudes and their lubricant fractions. A further assumption was that the Vis of all oils would fall between 0 and 100. 

TIED, A.K. A numerical simulation of finite-width thrust bearings, taking into account viscosity variation with temperature and pressure, J. Mech. Eng. Sci., J7, p. 1, (1975). 

The last term represents the correction for possible viscosity variation with temperature as discussed earlier. Equation (6-18) is valid for... 

R. Ratnagiri and C. E. Scott, Effect of Viscosity Variation with Temperature on the Compounding Behavior of Immiscible Blends, Polym. Eng. Sci. 39(9), 1823-1835 (1999). 

Figure 6.2 Viscosity variations with temperature and composition (SLS, soda-iime-siiica giass ALS, aluminosilicate glass according to Zarzycki, 1982).

Van Velzen s method provides an estimation of hydrocarbon viscosities and their variation with temperature ... 

The viscosity of a hydrocarbon mixture, as with all liquids, decreases when the temperature increases. The way in which lubricant viscosities vary with temperature is quite complex and, in fact, charts proposed by ASTM D 341 or by Groff (1961) (Figure 6.1) are used that provide a method to find the viscosity index for any lubricant system. Remember that a high viscosity index corresponds to small variation of viscosity between the low and high... 

For an incompressible fluid, the density variation with temperature is negligible compared to the viscosity variation. Hence, the viscosity variation is a function of temperature only and can be a cause of radical transformation of flow and transition from stable flow to the oscillatory regime. The critical Reynolds number also depends significantly on the specific heat, Prandtl number and micro-channel radius. For flow of high-viscosity fluids in micro-channels of tq < 10 m the critical Reynolds number is less than 2,300. In this case the oscillatory regime occurs at values of Re < 2,300. 

Seitz (31) measured the viscosity at 20°C of 77 soybean oils from four geographic locations, and the range of variation was 58.1cP to 62.2cP (Table 7). Viscosity decreases with temperature, and the relation is not linear. Kinematic values (viscosity/density) have been reported at 20°C and 80°C by Chioffi (91) and by Miller et al. (73) at frying temperatures (170-190°C) dynamic viscosities have been reported between 0°C and 100°C by Kravchenko et al. (65, 66), between 23.9°C and 110°C by Nourreddini et al. (67), between 20°C and 70°C by Alvarado... 

Figure 2.28 shows the variation of viscosity q with temperature for a polymer (28). In spite of the enormous change in q in passing through the glass transition, the behavior is qualitatively analogous to that seen for H or V. 

Figure 5 Variations with temperature of the steady state viscosity q of gluten from Olympic x Gabo cross line -/17 4- 18/-) in water (filled symbols) and in deuterium dioxide (empty symbols), q was obtained from the recovery curves...

The liquid viscosity varies with temperature = ix((T) and can be included in the analysis. However, when i, is evaluated at the average film temperature, this variation can be represented with sufficient accuracy. 

Figure 16 shows the steady shear relative viscosity variation with the effective Peclet number, Peeg, based on the effective particle diameter at each temperature level, and the temperature for a PMMA suspension. The particles of 0.8 pm are sterically stabilized by a thick layer of terminally anchored poly(dimethylsiloxane) and suspended in n-hexadecane at the volume fraction of 0 = 0.282. The data points are... 

Another similarity between amylose and cellulose is to be found in the variation of the limiting viscosity number with temperature. Cellulose derivatives are unique in having a large, negative, temperature dependence of viscosity. For amylose in dimethyl sulfoxide, it has been shown that the temperature coefficient of viscosity is again negative, although... 

Finally, it is important to highlight that the results presented here are valid under the hypothesis of thermophysical properties being independent of temperature. On the contrary the variation with temperature, especially for the fluid viscosity, cannot be ignored in particular for low Reynolds numbers when, for a prescribed wall heat flux, there is a strong temperature rise between the inlet and the outlet of the microchannel. Since the viscosity tends to decrease when the temperature increases, the viscous dissipation effects calculated by using the proposed constant properties model could be overestimated. 

The fluid viscosity and thermal conductivity experience the largest variation with temperature. Compared with the density and the specific heat variation, their influence on heat transfer is significantly higher, e.g. in the case of water. Therefore, density and thermal conductivity can in most cases be considered to be constant The fluid property variation becomes more important with decreasing diameter, where the axial variation is more pronounced than the variation over the cross-section of the channel. In contrast to the viscous dissipation, the significance of property variations increases with decreasing Br [53]. 

The effect of large changes in pressure at constant temperature on the viscosity of various hydrocarbons is shown in Figure 3. There we see that the logarithm of the viscosity of liquid hydrocarbons and hydrocarbon mixtures increases almost linearly with increasing pressure. Alternatively, viscosity can be considered to be a function of density rather than pressure, and this is used in several of the models discussed later. The kinematic viscosity shows similar trends with respect to these variables mentioned above, however its variation with temperature is significantly more linear than dynamic viscosity so that the former is somewhat easier to correlate than the latter. Consequently, some correlations have been developed exclusively for the kinematic viscosity, as will be discussed later. 

Empirical models to describe viscosity variations with lapsed time and elevated temperature have been proposed for the case of epoxy resins by some workers These isothermal models, however, seem to be inadequate, since the viscosity does not reach infinity within the gel time of the resin, according to these trratments. 

The viscosity data at P = 0.1 MPa, and its variation with temperature were either obtained from the literature (8,9) or measured by Ph. Vergne (10). At various P and T, the viscosity values were deduced from the W.L.F. equation whose parameters have been least square adjusted in the literature by Winer (11). 

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