Factors affecting viscosity of a liquid

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Introduction  It is the measure of stickiness of a fluid.  Refers to molecular friction caused by

pushing of molecules past one another.

 Water always has a low viscosity.  Other liquids such as shampoo or syrup have

high viscosity.

Factors Affecting Viscosity of a Liquid  Several factors affect viscosity of a liquid.  Flow conditions are among the factors .  The two main flow conditions of a liquid are

laminar and turbulent.

 Laminar flow is when the liquid moves in the

thin imaginary layers.

 Happens without changing of molecules from

one layer to the other.

 This flow is usually orderly.  Turbulent flow does not have a recognizable

structure.

 Layers cannot be observed.  Fluid develops cortices.  When tested under this flow condition, liquid

depicts higher viscosity.

 Shear rate is another factor that influences

liquid viscosity.

 Liquids that have internal flow that does not

depend on external forces

 That is the shear rate that act on the fluid.  They are ideally viscous.  Such fluids are called Newtonian fluids.

Newtonian liquids  They are ideally not viscous.  Viscosity of the non-Newtonian liquids changes with

shear rate.

 Apparent viscosity of such liquids is specified.  Some of them show shear-thinning behavior.  Their viscosity decrease with increasing shear rate.  Others have viscosity that increases with an increase

in shear rate.

Temperature Factor  Temperature has dominating influence in liquids

viscosity.

 Most have low viscosity when temperatures are high.  Decreased temperature causes increased liquid

viscosity.

 Viscosity and temperature have an inversely

relationship in liquids.

 Temperature changes affects the viscosity of a liquid.

Pressure  Pressure also affects viscosity of most liquids.  Compressing liquids at medium or low pressures is

almost impossible.

 This makes pressure not a intense factor to viscosity of

liquids.

 Changing pressure from about 0.1 to 30MPa can cause a

similar viscosity change.

 This is with a change in temperature of approximately 1

degree centigrade.



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