Transcript Temperature viscocity Dependence of olive oil - An

An-Najah National University
Faculty Of Science
Physics Department
Ahmed adel khlaif
Prof: Isam AL-Ashqar
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.
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
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.
Viscosity: 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.
In 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 .
a.
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).
 shear stress
 
 shear rate
Where, η is the dynamic viscosity in Pascal-second
(Pa.s); τ is shear stress (N/m2).
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
b.
• 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.
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.
The dynamic viscosity of water is 8.90 × 10^-4Pa·s or
8.90 × 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 1
centipoise 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.
The 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.
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.
To determine the value of Ƞ use any of theis formula …
1) Fulcher model
Ƞ=K (T-Tref) n
Where k, n: constant
T: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: constant
T: temperature(k)
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:
Constant
Value
SEE
k
637.7
1.15
n
-0.78
1.15
-For Arrhenius model:
Constant
Value
SEE
A
185
0.416
Ea
31.9
0.416
-For WLF model
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)
70
60
50
η(cp)
40
30
20
10
0
295
300
305
310
315
T(K◦)
320
325
330
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 .
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
The
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).
1) https://www.zotero.org/groups/vegetable_oil_fuel/items/itemKey/S5KW5C7V
2) http://acta.chem-soc.si/45/45-1-69.pdf
3) http://www.aqua-calc.com/what-is/dynamicviscosity/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.A
7.D8.AA
4)
http://www.brookfieldengineering.com/education/visc
osity_whymeasure.asp