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This module discusses how viscosity is characterized.

Introduction

All liquids have a natural internal resistance to flow termed viscosity. Viscosity is the result of frictional interactions within a given liquid and is commonly expressed in two different ways.

Dynamic viscosity

The first is dynamic viscosity, also known as absolute viscosity, which measures a fluid’s resistance to flow. In precise terms, dynamic viscosity is the tangential force per unit area necessary to move one plane past another at unit velocity at unit distance apart. As one plane moves past another in a fluid, a velocity gradient is established between the two layers ( [link] ). Viscosity can be thought of as a drag coefficient proportional to this gradient.

Fluid dynamics as one plane moves relative to a stationary plane through a liquid. The moving plane has area A and requires force F to overcome the fluid’s internal resistance.

The force necessary to move a plane of area A past another in a fluid is given by [link] where V is the velocity of the liquid, Y is the separation between planes, and η is the dynamic viscosity.

V/Y also represents the velocity gradient (sometimes referred to as shear rate). Force over area is equal to τ, the shear stress, so the equation simplifies to [link] .

For situations where V does not vary linearly with the separation between plates, the differential formula based on Newton’s equations is given in [link] .

Kinematic viscosity

Kinematic viscosity, the other type of viscosity, requires knowledge of the density, ρ, and is given by [link] , where ν is the kinematic viscosity and η is the dynamic viscosity.

Units of viscosity

Viscosity is commonly expressed in Stokes, Poise, Saybolt Universal Seconds, degree Engler, and SI units.

Dynamic viscosity

The SI units for dynamic (absolute) viscosity is given in units of N·S/m 2 , Pa·S, or kg/(m·s), where N stands for Newton and Pa for Pascal. Poise are metric units expressed as dyne·s/cm 2 or g/(m·s). They are related to the SI unit by g/(m·s) = 1/10 Pa·S. 100 centipoise, the centipoise (cP) being the most used unit of viscosity, is equal to one Poise.

[link] shows the interconversion factors for dynamic viscosity. [link] lists the dynamic viscosities of several liquids at various temperatures in centipoise. The effect of the temperature on viscosity is clearly evidenced in the drastic drop in viscosity of water as the temperature is increased from near ambient to 60 degrees Celsius. Ketchup has a viscosity of 1000 cP at 30 degrees Celsius or more than 1000 times that of water at the same temperature!

The interconversion factors for dynamic viscosity.
Unit Pa*S dyne·s/cm 2 or g/(m·s) (Poise) Centipoise (cP)
Pa*S 1 10 1000
dyne·s/cm 2 or g/(m·s) (Poise) 0.1 1 100
Centipoise (cP) 0.001 0.01 1
Viscosities of common liquids (*at 0% evaporation volume).
Liquid η (cP) Temperature(°C)
Water 0.89 25
Water 0.47 60
Milk 2.0 18
Olive Oil 107.5 20
Toothpaste 70,000-100,000 18
Ketchup 1000 30
Custard 1,500 85-90
Crude Oil (WTI)* 7 15

Kinematic viscosity

The CGS unit for kinematic viscosity is the Stoke which is equal to 10 -4 m 2 /s. Dividing by 100 yields the more commonly used centistoke. The SI unit for viscosity is m 2 /s. The Saybolt Universal second is commonly used in the oilfield for petroleum products represents the time required to efflux 60 milliliters from a Saybolt Universal viscometer at a fixed temperature according to ASTM D-88. The Engler scale is often used in Britain and quantifies the viscosity of a given liquid in comparison to water in an Engler viscometer for 200cm 3 of each liquid at a set temperature.

Questions & Answers

Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
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LITNING Reply
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LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
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LITNING
scanning tunneling microscope
Sahil
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Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
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Mahi
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Rafiq
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Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
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Source:  OpenStax, Physical methods in chemistry and nano science. OpenStax CNX. May 05, 2015 Download for free at http://legacy.cnx.org/content/col10699/1.21
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