viscosity_lectureS10

viscosity_lectureS10 - Viscosity of Liquids ¡ Objectives:...

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Unformatted text preview: Viscosity of Liquids ¡ Objectives: ¢ Determine how the components of a mixture affect the viscosity ¢ Determine how temperature affects the viscosity of a liquid ¡ Two mixtures: ¢ methanol – water ¢ toluene – p-xylene © 2006 D.B. King What is Viscosity? ¡ Resistance to flow ¢ high viscosity ⇒ does not flow easily ¢ low viscosity ⇒ flows easily ¡ Which has the higher viscosity? ¡ peanut butter or milk ¡ hot syrup or cold syrup ¡ water or glue © 2006 D.B. King Why measure viscosity? • Represents physical property of a system – for simple or complex systems – empirical index in quality-control applications • fundamental and intrinsic property of liquid as solvent – affects rate of mass transport, or diffusion, within the medium – affects chemical reaction kinetics Viscosity - mathematical treatment ¡ f = frictional drag bt layers ¡ η = viscosity of liquid ¡ dv/dr = velocity gradient bt layers ¢ v is greater closer to center ¢ this is a formulation of Newton’s Law of viscous flow ( ) r d v d L r f π η 2 − = © 2006 D.B. King Viscosity Units • Viscosity coefficient (η) unit called poise (P) 1 P = 1 dyne cm-2 s = 1 g cm-1 s-1 • Typical viscosities for liquids at room T ~ 0.002 –0.04 P often use centipoise(cP) = 10-2 P • SI units, η = Pa s = kg m-1 s-1 1 cP = 10-3 Pa s Poiseuelle’s Law • Describes mass transport through circular tube...
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This note was uploaded on 11/07/2011 for the course CHEM 356 taught by Professor Rowell during the Summer '10 term at Drexel.

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viscosity_lectureS10 - Viscosity of Liquids ¡ Objectives:...

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