Temperature Viscosity Dependence Of Olive Oil

An-Najah National UniversityFaculty Of Science

Physics Department

Ahmed adel khlaifProf: Isam AL-Ashqar

Abstract:-

Dynamic viscosities for a number of vegetable oils (unrefined sunflower oil, refined sunflower oil, olive oil, refined corn oil, unrefined pumpkin oil, a mixture of refined vegetable oil and unrefined pumpkin oil) were determined at temperatures from 298.15 K to 328.15 K. Some empirical relations that describe the temperature dependence of dynamic viscosity were fitted to the experimental data and the correlation constants for the best fit are presented.

Introduction:

In the food industry, viscosity is one of the most important parameters required in the design of technological process. On the other side, viscosity is also an important factor that determines the overall quality and stability of a food system.In the present study we determined the viscosities of some edible oils from vegetable sources in the temperature range from 298.15K to 328.15K.

Applicable empirical relations which describe the variation of dynamic viscosity with temperature were fitted to the experimental data and the correlation constants for thebest fit are presente

Why Measure Viscosity?

The ability to gather data on a material's viscosity behavior gives manufacturers an important "product dimension". Knowledge of a material's rheological characteristics is valuable in predicting pumpability and pourability, performance in a dipping or coating operation, or the ease with which it may be handled, processed, or used. The interrelation between rheology and other product dimensions often makes the measurement of viscosity the most sensitive or convenient way of detecting changes in color, density, stability, solids

content, and molecular weight.

DefinitionsViscosity: property by which fluids offer resistance to objects moving through them.

Ubbelohde viscometer: is a measuring instrument which uses a capillary based method of measuring viscosity.

Centipoise : is a dynamic viscosity measurement unit,cP is 10^-2

standard error of the estimate (SEE) : a measure of the accuracy of predictions

Saponification value(SV) :  the number of milligrams of potassium hydroxide required to saponify 1g of fat under the conditions specified.

Viscosity UnitsIn the SI System (System International d'Unités) the dynamic viscosity units are N·s/m2 ≡ Pa·s, where N is Newton and Pa is Pascal. The dynamic viscosity is often expressed in the centimeter-gram-second system (CGS) as g/cm·s, dyne·s/cm2 or poise (P) where, 1 poise =dyne·s/cm2 =g/cm·s = 10-1 Pa·s

Conversions:1000 m Pa.s = 1 Pa.s = 1Ns/m2

100 cP = 0.1 Pa.s = 100 m Pa.s =1 dyne.s/cm2 .

Viscosity Coefficientsa. Dynamic viscosity (η): the ratio of shear stress

(force over cross section area) to the rate of deformation (the difference of velocity over a sheared distance).

Where, η is the dynamic viscosity in Pascal-second (Pa.s); τ is shear stress (N/m2).

b. The Kinematic viscosity requires knowledge of mass density of the liquid (ρ) at that temperature and pressure. It is defined as: ν= η/ ρ

Where, ν is kinematic viscosity in centistokes (cSt), ρ is in g/cm3

rateshear

stressshear

Forms Of Viscosity• Newtonian: fluids, such as water and most gases which have a constant viscosity.• Shear thickening: viscosity increases with the rate of shear.• Shear thinning: viscosity decreases with the rate of shear. Shear thinning liquids are very commonly, but misleadingly, described as thixotropic.• Thixotropic: materials which become less viscous over time when shaken, agitated, or otherwise stressed.• Rheopectic: materials which become more viscous over time when shaken, agitated, or otherwise stressed.• A Bingham plastic is a material that behaves as a solid at low stresses but flows as a viscous fluid at high stresses.• A magnetorheological fluid is a type of "smart fluid" which, when subjected to a magnetic field, greatly increases its apparent viscosity, to the point of becoming a viscoelastic solid.

What Is The Relationship Between Temperature And Viscosity Of Liquids And Gases?

Viscosity of a liquid or gas is the opposition a fluid or gas gives when under shear stress or tensile stress. It is the thickness of its internal friction. The relationship between viscosity and temperature is that higher temperatures decrease the viscosity and low temperatures increase it.

Viscosity Of WaterThe dynamic viscosity of water is 8.90 × 10^-

4Pa·s or8.90 × 10^-3 dyn·s/cm2 or 0.890 cP at about 25 °C.Water has a viscosity of 0.0091 poise at 25 °C, or 1centipoise at 20 °C.As a function of temperature T (K): (Pa·s) = A ×10B/(T-C)

where A=2.414 × 10^-5 Pa·s ; B = 247.8 K ; and C = 140K .Viscosity of liquid water at different temperatures up to the normal boiling point is listed below.

Viscosity Of AirThe viscosity of air depends mostly on the temperature. At 15.0 °C, the viscosity of air is 1.78×10−5 kg/(m·s), 17.8 μPa.s or 1.78×10−5 Pa.s.. One can get the viscosity of air as a function of temperature from the Gas Viscosity Calculator.

Is There A Relation Between Viscosity And Density?

You said that there is no obvious relationship between density & viscosity. I disagree. If you heat a liquid, you increase it's volume because as the molecules are heated, they move & take up more space. The mass of the liquid, on the other hand, has not changed. Since the formula for density is mass divided by volume, the density of a heated liquid may change because its volume has changed, very slightly, but changed.

TheoryTo determine the value of Ƞ use any of theis formula …

1) Fulcher model

  Ƞ=K (T-Tref) n

Where k, n: constantT:temperature(K)Tref : referance temperature(K).

2) Arrhenius model

Ƞ=A eEa/RT

Where Ea: activation energy (KJ/Kg)

R:universal gas(constant)(8.314kJ/kg. mol. k)T:absoulute temp(k)A:constant(mpa.s).

3) William- landel Ferry model

Ln (η) =a/(b+T)Where a , b: constantT: temperature(k)

Standard Error Estimate(see)

To obtain the value of SEE , apply this equation :

where n:nomber of data point.P:nomber of parameter in each equation.Ƴi:oil viscosity at particular temperature.Ƴi':predicted viscosity from equation's

-For Fulcher model:

-For Arrhenius model:

-For WLF model

Constant Value SEE

k 637.7 1.15

n -0.78 1.15

Constant Value SEE

A 185 0.416

Ea 31.9 0.416

Constant Value SEE

a 1.005 0.027

b -224.8 0.027

328.15 318.5 308.15 298.15 T(k)

21.03 28.99 41.67 63.28 η(cp)

295 300 305 310 315 320 325 3300

10

20

30

40

50

60

70

T(K◦)

η(c

p)

Chemical Characteristics Affected The Viscosity Of Olive Oil.

The composition of olive oil primarily triacylglycerols and secondarily free fatty . Viscosity for oil has direct relation with the chemical characteristic like Iodine value (IV) (degree of unsaturation) and saponification value (SV) (the chain length of fatty acid), this relation describes the variation of viscosity with (IV) and (SV) for oil

:Ln(η)=-4.7965+2525.92962(1/T) +1.6144[(SV)2/T2]-101.06*10-7(IV)2 .

The oil's with more double bonds appeared to have lower viscosity, and oil with more single bonds appeared to have higher viscosity .

Interesting Facts On Viscosity:

When measuring viscosity with any type of viscometer, accurate temperature is so important that viscosity can double with a change of only 5 Celsius

The viscosity of gases is approximately proportional to the square root of temperature

Rheology is the study of viscosity

ConclusionThe viscosity of olive oil decrease with increasing temperature.

Oil with more double bonds have lowest viscosity and the other with more single bond have high viscosity.

William landel ferry model is the best model to find value of Ƞ ,because it's the lowest standard error of estimate (SEE).

Referance1) https://www.zotero.org/groups/vegetable_oil_fuel/items/itemKey/S5KW5C7V

2) http://acta.chem-soc.si/45/45-1-69.pdf3) http://www.aqua-calc.com/what-is/dynamic-viscosity/centipoisehttp://ar.wikipedia.org/wiki/%D9%84%D8%B2%D9%88%D8%AC%D8%A9#.D9.84.D8.B2.D9.88.D8.AC.D8.A9_.D8.A7.D9.84.D8.BA.D8.A7.D8.B2.D8.A7.D8.AA4) http://www.brookfieldengineering.com/education/viscosity_whymeasure.asp