Dynamic and Kinematic Viscosities

The viscosity p referred to above is more correctly called the dynamic viscosity, and should not be confused with v, the kinematic viscosity. The kinematic viscosity is the ratio of dynamic viscosity to fluid density, v = nip [=] L2 T x, m2 s x. 

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The classification criteria refer to kinematic viscosity. The following provides the conversion between dynamic and kinematic viscosity ... 

FIGURE 8.29 The dependence of dynamic and kinematic viscosity on the Cu/C nanocomposite quantity. 

Table 20.4 Dynamic and kinematic viscosity, rf and v (= rjlp), of various substances at 293 K.

Viscoelasticity. When in addition, the flnid or the material stores some capacitive energy, an elastic property comes in snpplement to the dynamic and kinematic viscosities for featuring the system. The storage and the transport of capacitive energy is then supported by a combined property of viscoelasticity, analogous to a kinetic constant in physical chemistry (see case study All Reactive Chemical Species in Chapter 4 and case stndy 116 Viscoelastic Relaxation in Chapter 11). 

In the SI system, the theoretical unit of v is m2/s or the commonly used Stoke (St) where 1 St = 0.0001 m2/s = 100 cSt = 100 centiStoke. Similarly, 1 centiStoke = 1 cSt = 0.000001 m2/s = 0.01 Stoke = 0.01 st. The specific gravity of water at 20.2°C (68.4°F) is almost 1. The kinematic viscosity of water at 20.2°C (68.4°F) is for all practical purposes equal to 1 cSt. For a liquid, the kinematic viscosity will decrease with higher temperature. For a gas, the kinematic viscosity will increase with higher temperature. Another commonly used kinematic viscosity unit is Saybolt universal seconds (SUS), which is the efflux time required for 60 mL of petroleum product to flow through the calibrated orifice of a Saybolt universal viscometer, as described by ASTM-D88. Therefore, the relationship between dynamic viscosity and kinematic viscosity can be expressed as... 

Source The Engineering Toolbox, Dynamic, Absolute and Kinematic Viscosity, 2007. Available at http //www.engineeringtool-box.com/dynamic-absolute-kinematic-viscosity-d 412.html. With permission. 

The viscosity of a fluid is highly temperature dependent and, for either dynamic or kinematic viscosity to be meaningful, the reference temperature must be quoted. In ISO 8217 the reference temperature for a residual fluid is 100°C. For a distillate fluid the reference temperature is 40°C. 

Therefore, to summarize, in the SI system, dynamic viscosity is expressed as pascal seconds and kinematic viscosity is expressed as square meters per second. In practice, dynamic viscosities are reported as millipascal seconds (mPa-s). Base stock viscosities are usually reported as kinematic viscosities. 

Conversion factors for mass, density, pressure, energy, specific energy, specific heat, thermal conductivity, dynamic viscosity, and kinematic viscosity in different systems of units are also given in Chap. 2 (Tables 2.1-2.9). 

In general, viscosity is defined as the fundamental property of liquids by virtue of which they show resistance to flow or shear. Viscosity has been broadly classified into two groups, namely, dynamic viscosity and kinematic viscosity. Dynamic viscosity (also known as absolute viscosity)... 

Viscosity is a notion somewhat confused in fluid mechanics becanse it encompasses two very different properties The dynamic viscosity t] and the kinematic viscosity V. These archaic adjectives dynamic and kinematic are misleading because there is no real notion of time or movement involved in these systan properties. 

The viscosity of a liquid hydrocarbon mixture that is not well characterized is required in many industrial applications, of which crude oils and crude cuts are typical examples. Many correlations have been proposed for the dynamic or kinematic viscosity of such mixtures based on some selected (usually specifically measured) characteristics of the mixture. Puttagunta and co-workers introduced several such correlations [33-36]. These correlations are all empirical in nature and require at least one viscosity measurement for the mixture in addition parameters of the model(s) have been fit to certain hydrocarbon mixtures. 

Viscosity is a key lube oil property and is a measure of the fluidity of the oil. There are two measures of viscosity commonly used kinematic and dynamic. The kinematic viscosity is flow due to gravity and ranges from approximately 3 to 20 cSt (centistokes) for solvent neutrals and about 30-34 cSt at 100°C for Bright stock. The dynamic viscosity is flow due to applied mechanical stress and is used to measure low temperature fluidity. Brookfield viscosity for automobile transmission fluids (ATF s) at -40°C and cold cranking simulator (CCS) viscosity for engine oils at -25°C are examples of dynamic viscosity measurements. 

There is some equipment to be used for viscosity measurement which broadly classified into two categories dynamic and kinematic viscometer. A dynamic viscometer is one of the shear rate can be controlled and measured (rotational viscometer). It is the only typ>e of viscosity measurement that is relevant to fluids where the viscosity is related to the shear rate (non-Newtonian fluids). A kinematic viscometer is where the shear rate can neither be controlled nor measured, for example capillary viscometer. 

Absolute viscosity is the ratio of shear stress to shear rate. It is a fluid s internal resistance to flow. The common unit of absolute viscosity is the poise (IP = 100 cps). Absolute viscosity divided by fluid density equals kinematic viscosity. It is occasionally referred to as dynamic viscosity. Absolute viscosity and kinematic viscosity are expressed in fundamental units. Acid number... 

Viscosity is a measure of a fluid s internal resistance to flow and may be thought of as a measure of fluid friction. Two different viscosity coefficients have been described, dynamic viscosity, the more usual one which is defined in Pascal-second (Pa.s, SI unit) or centipoises (cP, where 1 cP = 0.001 Pa.s) and kinematic viscosity that is the dynamic viscosity divided by the density (normally in m. s i or centistokes). 

The kinematic viscosity v is the ratio of the dynamic viscosity /x and density p ... 

Dynamic similarity requires geometric and kinematic similarity in addition lo force ratios at corresponding points being equal, involving properties of gravitation, surface tension, viscosity and inertia [8, 21]. With proper and careful application of this principle scale-up from test model lo large scale systems is often feasible and quite successful. Tables 5-... 

Kinematic viscosity is the ratio of dynamic viscosity and density, and can be obtained by dividing the dynamic viscosity of a fluid with its mass density, as shown by Equation 18.2 ... 

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. 

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