Kinematic viscosity of water

IABLE 10 1 Density/ Viscosity/ and Kinematic Viscosity of Water and Air in Terms of Temperature... 

The property of the fluid which appears in the Reynolds number is the kinematic viscosity pfp. The kinematic viscosity of water at 294 K and atmospheric pressure is 10 6 m2/s compared with 15.5 x 10 6 nr/s for air. Thus, gases typically have higher kinematic viscosities than liquids at atmospheric pressure. 

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... 

The usual specific flow-rates for extraction are very small. In terms of space velocities, these are about 5 to 15 kg/h per litre of extractor volume, with superficial velocities in the range of 0.5 to 10 mm/s. With these small velocities, natural convection mass transfer is the favoured mechanism of transport. Gas densities are in the range of 500 to 800 kg/m3, and viscosities are about 5 x 10 7 kg/(m s), thus giving kinematic viscosities of about 10 9 m2/s, which is a very small value for a fluid. For example, the kinematic viscosity of water is 10"7 m2/s and that of ambient air is 2 x 10 5 m2/s. This makes free convection a principal mechanism for mass-transfer in high pressure gases. 

In developing the arguments that are presented later in this review, it is necessary to keep in mind the relative scales (dimensions) at which each phase occurs. This is important because the effect of flow on localized corrosion is largely (though not totally) a question of the relative dimensions of the nucleus and the velocity profile in the fluid close to the surface. However, the velocity profile is a sensitive function of the kinematic viscosity, which in turn depends on the density and the dynamic viscosity. Because the kinematic viscosity of water drops by a factor of more than 100 on increasing the temperature from 25 °C to 300 °C, the conclusions drawn from ambient temperature studies of the effect of flow on localized corrosion must be used with great care when describing flow effects at elevated temperatures. 

Table 3. Variation of the kinematic viscosity of water and the Schmidt number for hydrogen in water as a function of temperature.

Describe the steady-state distribution of l-/xm diameter clay particles and 0.01 -/un diameter clay particles in still water. For each particle size, calculate the depth above the bottom of the water column at which the particle concentration is one-half the particle concentration at the bottom. Assume a kinematic viscosity of water of 0.013 cm2/sec at 50°F and a solid particle density of 2.6 g/cm3. 

A river of 2-m depth moving at an average velocity of 0.2 m/sec receives particles of 200-/r,m diameter from a storm drain emptying at the river surface. Assume that the particles are of mineral origin with a density of approximately 2.6 g/cm3 and that the kinematic viscosity of water is 1.3 X 10-2 cm2/sec (at 10°C). What is the minimum distance the particles will travel before settling to the river bottom ... 

The blood-phase oxygen transfer coefficient kB is estimated by Equations 14.11 to 14.13. Oxygen diffusivity in water at 20°C, D0zW —2.07x10 5cm2s kinematic viscosity of water at 20 °C, vw = 0.010 cm2 s oxygen diffusivity in... 

Dispersion and gas exchange rates in unconfmed natural water systems can be determined using two volatile gaseous tracers with different gas exchange rates if the ratio of the gas exchange rates is known. The gas exchange rate of a gas is proportional to the Schmidt number (defined as the kinematic viscosity of water divided by the molecular diffusivity of the gas in water) of the gas raised to an exponent n (Jahne et al. 

The kinematic viscosity of water at room temperMure is 1 cSt.) To avoid confusion over which visbosity is being used, some writers refer to the viscosity fj, as the absolute viscosity. In Chap. 6 we will see some examples of the practical convenience ofj the kinematic viscosity. 

For this second relation, dual tracer experimenters have used a power law dependence of gas transfer velocities on Schmidt number (the ratio of kinematic viscosity of water to the diffusivity of the gas) ... 

For a rotating-disc electrode with a radius r = 1 cm in an aqueous electrolyte (kinematic viscosity of water 0.01 cm s at 20 °C) the critical rotation rate is 10,000 rot min. ... 

The kinematic viscosity of water (v) is calculated from the temperature function for the dynamic viscosity given by Eq. (7.1) and the temperature function for the density given by Eq. (7.2). 

Centistoke (cs) n. (1) A deprecated, but still used unit of kinematic viscosity, 0.01 Stoke, the approximate kinematic viscosity of water at 20° C. The SI equivalent is 1 cs = 10 m /s. (2) One one-hundredth of a stoke, which is the unit of kinematic viscosity ... 

The Schmidt number, Sc=v/D, is the ratio between two transport coefficients, where D is the molecular diffusion coefficient. Sc can be interpreted as the ratio of two rates. The rate at which concentration becomes smoothed out by molecular diffusion is proportional to (Dt) where t denotes the time, whereas the rate for motion to spread out or die is proportional to (vt) The ratio of these two rates is Sc. Thus, if Sc S> 1, as in the case of liquids, concentration fluctuations survive without being erased by mechanical mixing until late in the process. The kinematic viscosity of water is about 10 m s . The diffusion coefficient of small molecules in water is about 10 m s hence a typical value of Sc for a liquid such as water is about 1000. 

Referring to Table 2-7 (or Table 2-8 for USCS units), the kinematic viscosity of water is 0.89 X 10" mVs. We need to determine the coefficient Cs = The curves... 

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