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4 April, 14:44

For this device the liquid to be tested is drawn into the tube to a level above the top etched line. The time is then obtained for the liquid to drain to the bottom etched line. The kinematic viscosity, ν, in m2/s is then obtained from the equation ν = KR4t where K is a constant, R is the radius of the capillary tube in mm, and t is the drain time in seconds. When glycerin at 20 ˚C (υ=1.19·10-3 m2/s) is used as a calibration fluid in a particular viscometer the drain time is 1430 s. When a liquid having a density of 970 kg/m3 is tested in the same viscometer the drain time is 900 s. What is the dynamic viscosity of this liquid?

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  1. 4 April, 17:42
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    The dynamic viscosity of the liquid is 0.727 kg/m*s

    Explanation:

    In the equation for that viscosimeter, ν = KR⁴t, the terms K and R are not dependent on the liquid that is being tested, unlike ν and t.

    Using that equation and the data given in the problem, we can calculate the product of K and R⁴.

    1.19*10⁻³m²/s = (KR⁴) * 1430 s

    KR⁴=8,32*10⁻⁷m²/s²

    We can now calculate the kinematic viscosity of the unknown liquid.

    ν=8,32*10⁻⁷m²/s²*900s

    ν=7.49*10⁻⁴m²/s

    The relationship between the kinematic viscosity and the dynamic viscosity is given by the equation μ=ν * ρ, where μ is the dynamic viscosity and ρ is the density. Thus:

    μ=7.49*10⁻⁴m²/s * 970 kg/m³

    μ=0.727 kg/m*s
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