Viscosity empirical units

Viscosity measurements are expressed in either systematic or empirical units both are used, but the current trend is very much toward using systematic units. 

However, empirical units have left a lasting impression on terminology, and while still employed from time to time in providing names for base stocks (e.g., 100N, 250N), their actual viscosity measurements and their ranges on specification sheets are measured in systematic units and converted to empirical... 

Where ij. is defined as the kinematic viscosity (centistokes), and is a constant with a value of 2,213.8 in USCS units and 353.68 in SI units. An empirical relation for the Fanning friction factor is the Colebrook-White equation ... 

SMD = 0.07lf v/ gM - 1 pVul y/3 in cm (cgs units) / Derived by empirically correcting a theoretical equation of inviscid flows for viscosity with fan spray data of wax Valid for 3[Pg.259]

The Saybolt Universal and Saybolt Furol viscometers are widely used in the United States and the Engler in Europe. In the United States, viscosities on the lighter fuel grades are determined using the Saybolt Universal instrument at 38°C (100°E) for the heaviest fuels the Saybolt Enrol viscometer is used at 50°C (122°E). Similarly, in Europe, the Engler viscometer is used at temperatures of 20°C (68°E), 50°C (122°E), and in some instances at 100°C (212°E). Use of these empirical procedures for fuel oils is being superseded by kinematic system (ASTM D396 BS 2869) specifications for fuel oils. 

Newtonian Viscosity in Glasses. As we saw in Chapter 1, the structure of glasses is fundamentally different from metals. Unlike metals and alloys, which can be modeled as hard spheres, the structural unit in most oxide glasses is a polyhedron, often a tetrahedron. As a result, the response of a structural unit to a shear force is necessarily different in molten glasses than in molten metals. The response is also generally more complicated, such that theoretical descriptions of viscosity must give way completely to empirical expressions. Let us briefly explore how this is so. 

Chapter HI relates to measurement of flow properties of foods that are primarily fluid in nature, unithi.i surveys the nature of viscosity and its relationship to foods. An overview of the various flow behaviors found in different fluid foods is presented. The concept of non-Newtonian foods is developed, along with methods for measurement of the complete flow curve. The quantitative or fundamental measurement of apparent shear viscosity of fluid foods with rotational viscometers or rheometers is described, unithi.2 describes two protocols for the measurement of non-Newtonian fluids. The first is for time-independent fluids, and the second is for time-dependent fluids. Both protocols use rotational rheometers, unit hi.3 describes a protocol for simple Newtonian fluids, which include aqueous solutions or oils. As rotational rheometers are new and expensive, many evaluations of fluid foods have been made with empirical methods. Such methods yield data that are not fundamental but are useful in comparing variations in consistency or texture of a food product, unit hi.4 describes a popular empirical method, the Bostwick Consistometer, which has been used to measure the consistency of tomato paste. It is a well-known method in the food industry and has also been used to evaluate other fruit pastes and juices as well. 

A third water-soluble substrate for endocellulase is hydroxyethyl-cellulose (HEC). As early as 1931, Ziese (5) used HEC and Sandegren et al. (6) defined the activity as being proportional to the change of the inverse of the specific viscosity per time unit. Child et al. (7) have also used HEC and based their calculation -on a linearization of the viscosity measurements according to Eriksson et al. (8). They defined an enzymic activity unit as the amount of enzyme causing a viscosity change of 0.001 rjre 126 min"1. The exponential factor was used in order to linearize the data. This unit is useful for comparison of cellulases of different origin, but it is based on an empirical relationship. The authors made an evaluation of their method in comparison with CMC hydrolysis. 

Liquid sulfur-dicyclopentadiene (DCP) solutions at 140°C undergo bulk copolymerization where the melt viscosity and surface tension of the solutions increase with time. A general melt viscosity equation rj == tj0 exp(aXH), at constant temperature, has been developed, where tj is the viscosity at time t for an S -DCP feed composition of DCP mole fraction X and rj0 (in viscosity units), a (in time 1), and b (a dimensionless number, -f- ve for X < 0.5 and —ve for X > 0.5) are empirical constants. The structure of the sul-furated products has been analyzed by NMR. Sulfur non-crystallizable copolymeric compositions have been obtained as shown by thermal analysis (DSC). Dodecyl polysulfide is a viscosity suppressor and a plasticizer for the S8-DCP system. 

A general exponential equation (see Appendix for detailed discussions) of the form tj = rj0 exp (aXbt), at constant temperature, has been developed to predict the viscosity (97, CP) as a function of feed composition (X, mol fraction of DCP) and time (t, hr) rj0, a, and b are empirical constants rj0 is the viscosity at t = 0, a is in units of reciprocal time, and b is dimensionless. The assumptions made here are ... 

Because of the similarity between the mechanisms of viscous flow, diffusion and electrical conductivity, which are all activated processes, a relationship between these phenomena was sought. It has been established empirically that the temperature dependence of viscosity and resistivity of glass melts are often mutually dependent according to the relationship log t/ 3 log 2, or log = a log — b (cf. Morey, 1954). However, it should be borne in mind that mobility of cations is critical for transfer of electric charges while mobility of anionic structural units (network formers) is involved in the case of vi.scous flow. This is why the relation between the two quantities is difficult to interpret. 

G is an empirical constant, with units of length per unit time, determined experimentally, and the exponent, n, is predicted to vary between V2 and 1. The ratio of the kinematic viscosity to diffusion coefficient is called the Schmidt number. Sc (Table 10.1) ... 

The viscosities of polymer solutions and of polymer melts have some very important common features, which are related to the fundamental nature of the motions of polymer chain segments [4,8,10] resulting in the flow of macromolecular chains. At an empirical level, one manifestation of these interrelationships is that Mcp which is the key material parameter determining the molecular weight dependence of the melt viscosity, can be estimated from the intrinsic viscosity of the polymer under 0 conditions, which was discussed in Chapter 12. If K -Mci.0-5 is expressed in units of cc/grams, then Mcr can be predicted [7] (but only to within a factor of two) by using Equation 13.6. 

The best known and most used empirical method is that of O Connell (Figure 12.60), for distillation columns and absorbers. The curves are based on plant data for several bubble-cap columns plus a few pilot-scale units. Efficiency is related to two properties of the feed mixture liquid viscosity and relative volatility a. Higher values of the p a product indicate larger liquid-side mass transfer resistance and hence a lower efficiency. For a vapor feed or a mixed vapor-liquid feed, the correlating viscosity should be that of the feed tray liquid. 

Texture. A hard biscuit has a crisp or brittle texture. This implies that it deforms in a fully elastic manner upon application of a force, until it breaks (snaps) at a relatively small deformation. Breakage goes along with a snapping sound. It appears from empirical observations that a crisp material has an apparent viscosity of at least 1013 or 1014 Pa s. The water content or temperature above which crispness is lost closely corresponds to Tg. Sensory evaluation shows that an increase in water content by 2 or 3 percentage units, or in temperature by 10 or 20 K, can be sufficient to change a crisp food into a soft (rubbery) material. 

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