It is a U shaped tube with one side having a capillary orifice. It is used to determine viscosity of Newtonian fluids. The time required for the liquid to pass vertically between two marks of the capillary under the effect of gravity is indicative of viscosity. Liquids with larger viscosity require more time to pass between the same marks. The following equation is used to determine viscosity of a liquid:
Example:
Calculate the viscosity of a given solution at 20 ºC that required 90 seconds to pass between the preset marks of a capillary viscometer and has a density of 1.03 g/ cm3 . Assuming that water (density = 1.00 g/cm3 ) required 35 seconds to pass between the marks and has a viscosity of 1.00 centipoise (cp) at 20 ºC.
Answer:
η1/ η2 = (ρ1 × t1)/ (ρ2 × t2)
Where η1 is the viscosity of the tested liquid, η2 is the viscosity of a known liquid (e.g.water), ρ1 and ρ2 are the densities of the tested and known liquids respectively, t1 is the time required for the tested liquid to pass between two preset marks on the viscometer, and t2 is the time required for the known liquid to pass between the marks.
Example:
Calculate the viscosity of a given solution at 20 ºC that required 90 seconds to pass between the preset marks of a capillary viscometer and has a density of 1.03 g/ cm3 . Assuming that water (density = 1.00 g/cm3 ) required 35 seconds to pass between the marks and has a viscosity of 1.00 centipoise (cp) at 20 ºC.
Answer:
η1/ η2 = (ρ1 × t1)/ (ρ2 × t2)
η1/ 1.00 cp = (1.03 g/ cm3 × 90 sec.)/ (1.00 g/ cm3 × 35 sec.)
η1 = (92.7)/ (35.0)
η1 = 2.65 cp
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