1. Viscosity & conductance
Part 10

2. Introduction Kinematic Viscosity :
Viscosity is a quantitative measure of a fluid’s resistance to flow.
Dynamic (or Absolute) Viscosity:
The dynamic viscosity(η) of a fluid is a measure of the resistance it offers to relative shearing motion الحركة القصية.
η= F/ [A×(u/h)]
η= τ /(u/h) N-s/m²
Kinematic Viscosity :
It is defined as the ratio of absolute viscosity to the density of fluid.
ν= η/ρ m²/s ; ρ= density of fluid

3. Viscosity Measurements
Capillary Viscometers
It gives the ‘kinematic viscosity’ of the fluid. It is based on Poiseuille’s law for steady viscous flow in a pipe.

4. Viscosity Measurements
Rotational Viscometers
These viscometer give the value of the ‘dynamic viscosity’.
It is based on the principle that the fluid whose viscosity is being measured is sheared between two surfaces.
In these viscometers one of the surfaces is stationary and the other is rotated by an external drive and the fluid fills the space in between.
The measurements are conducted by applying either a constant torque and measuring the changes in the speed of rotation or applying a constant speed and measuring the changes in the torque.
There are two main types of these viscometers: rotating cylinder and cone-on-plate viscometers

5. Viscosity Measurements
Rotating cylinder viscometer

6. Viscosity Measurements
Cone-on-plate viscometer

7. Effects of temperature
The viscosity of liquids decreases with increase the temperature.
The viscosity of gases increases with the increase the temperature.

8. Effects of temperature
The lubricant oil viscosity at a specific temperature can be either calculated from the viscosity - temperature equation or obtained from the viscosity-temperature ASTM chart.
Viscosity-Temperature Equations

9. Effects of temperature
fig: Viscosity-temperature characteristics of selected oils

10. Viscosity index VI = (L - U)/ (L - H) * 10
An entirely empirical parameter which would accurately describe the viscosity- temperature characteristics of the oils.
The viscosity index is calculated by the following formula:
VI = (L - U)/ (L - H) * 10
where ,
VI is viscosity index
U is the kinematic viscosity
of oil of interest
L and H are the kinematic
viscosity of the reference oils
Fig . Shows the evaluation of viscosity index

11. Effects of pressure Lubricants viscosity increases with pressure.
For most lubricants this effect is considerably largest than the other effects when the pressure is significantly above atmospheric.
The Barus equation :

12. Effects of pressure

13. Viscosity - shear relationship
For Newtonian fluids, shear stress linearly vary with the shear rate as shown in Figure. Viscosity is constant for this kind of fluid.
τ = η (u/h)
Non Newtonian fluid doesn’t
follow the linear relation
between viscosity and shear rate.

14. Viscosity – shear relationship
Pseudoplastic Behaviour
Pseudoplastic or shear thinning and is associated with the thinning of the fluid as the shear rate increases.
Thixotropic Behaviour
Thixotropic or shear duration thinning, is associated with a loss of consistency of the fluid as the duration of shear increases.
The opposite of this behavior is
known as inverse thixotropic.

15. Applications Selection of lubricants for various purpose.
- we can choose an optimum range of viscosity for engine oil.
- for high load and also for speed operation high viscous lubricants is required.
In pumping operation
- for high viscous fluid high power will require.
- for low viscous fluid low power will require.
In making of blend fuel
- less viscous fuels easy to mix.
In the operation of coating and printing.

16. Viscosity definations
A measure of the resistance of flow due to internal friction when one layer of
fluid is caused to move in relationship to another layer. The Poise represents absolute
viscosity, the tangential force per unit area of either of two horizontal planes at unit
distance apart, the space between being filled with the substance. A liquid with an absolute
viscosity of one Poise requires a force of one dyne to maintain a velocity differential of one
centimeter per second over a surface one centimeter square.
When the ratio of shearing stress to the rate of shear is constant, as is the case with water and thin motor oils, the fluid is called a Newtonian fluid. In the case of non- Newtonian fluids, the ratio varies with
the shearing stress, and viscosities of such fluids are called apparent viscosities.
In the new SI system, it is proposed that values for the Poise be stated as Pascal seconds, the
conversion factor being 1 Poise equal to 1 × 10-1
Pa·s. A common measurement unit is the
milliPascal second (mPa·s). Conversion factors are as follows:
1 centipoise (cP) = 0.01 poise (P)
1 Pa·s = 10 P
1 cP = Pa·s = 1 mPa·s
1 Pa·s = 1000 cP

17. Viscosities
Absolute Viscosity: The tangential force per unit area of two parallel planes at unit distance apart
when the space between them is filled with a fluid and one plane moves with unit velocity in
its own plane relative to the other. Also known as coefficient of viscosity.
Apparent Viscosity : The value obtained by applying the instrumental equations used in obtaining the viscosity of a Newtonian fluid to viscometer measurements of a non-Newtonian fluid. .
Dilute Solution Viscosity: The viscosity of a dilute solution of a polymer,
measured under prescribed conditions, is an indication of
the molecular weight of the polymer and can be used to
calculate the degree of polymerization

18. (mm2/s). Conversion factors are as follows:
Kinematic Viscosity: The absolute viscosity of a fluid divided by the density of the fluid. Also known
as the coefficient of kinematic viscosity. Measured in stokes (St) or centistokes (cSt). One
centistoke = 0.01 stokes. The metric unit is square metres per second (m2/s). A common
metric measurement unit in glass capillary viscometry is millimeters squared per second
(mm2/s). Conversion factors are as follows:
1 St = 1 x 10-4m2/s
1 m2/s = 10,000 St
1 cSt = 1 x 10-6m2/s = 1 mm2/s
1 m2/s = 1,000,000 cSt
Centistokes may be converted to centipoise (cP) by multiplying by the density of the fluid
being measured, all measured at the same temperature

19. Intrinsic Viscosity ([η]): The ratio of a solution’s specific viscosity to the concentration of the
solute, extrapolated to zero concentration.
Intrinsic viscosity reflects the capability of a polymer in solution to enhance the viscosity of the solution.
The viscosity behavior of macromolecular substances in solution is one of the most frequently used approaches for characterization.
The intrinsic viscosity number is defined as the limiting value of the specific viscosity/concentration ratio at zero concentration.
Intrinsic viscosity is determined by measuring the relative viscosity at several different concentrations and then extrapolating the specific viscosity to zero concentration. The variation of the viscosity number with concentration depends on the type of molecule as well as the solvent. In general, the intrinsic viscosity of linear macromolecular substances is related to the molecular weight or degree of polymerization. With linear macromolecules, viscosity number measurements can provide a method for the rapid determination of molecular weight when the relationship between viscosity and molecular weight has been established. Intrinsic viscosity is
calculated by determining the reduced viscosity (ηsp/c) and extrapolating to infinite dilution.
Huggins equation
c → 0
η = ηred

20. Craemer equation
η = lim ηinh
Where: c = concentration of polymer in grams per 100 milliliters of solution Also known as LIMITING VISCOSITY NUMBER.
Inherent Viscosity (ηinh): The quotient of the natural logarithm of
relative viscosity and the concentration.
Inherent viscosity (ηinh) is expressed in the following equation:
η red=ηrel-1/c

21. Relative Viscosity (ηrel): The ratio of the viscosities of the polymers olution (of stated concentration) and of the puresolvent at the same temperature.
Also known as SOLUTIONSOLVENT VISCOSITY RATIO.
Specific Viscosity (ηsp) The relative viscosity of a polymer solution of known concentration minus 1;
usually determined at low concentration of the polymer; for example, 0.5 gram per 100
milliliters of solution, or less.

22. Electrical conductance
Thank you
The next part will be
Electrical conductance

23. Conductivity
PART 11

24. Conductivity A measure of how well a solution conducts electricity
Water with absolutely no impurities (does not exist)
Conducts electricity very poorly
Impurities in water increase conductivity
So, when measure conductivity of water can estimate the degree of impurities

25. Conductivity The current is carried by dissolved ions
The ability of an ion to carry current is a function of:
Ions charge (more charge, more current)
Ions mass or size (larger ions, conduct less)

26. Electrolytes Electrolytes Strong electrolytes Weak electrolytes
Substances whose aqueous solution is a conductor of electricity
Strong electrolytes
All the electrolyte molecules are dissociated into ions
Weak electrolytes
A small percentage of the molecules are dissociated into ions
Nonelectrolytes
None of the molecules are dissociated into ions

27. Dissociation of Water

28. Electrolytes

29. Strength of Solutions Conductivity of various solutions
Conductivity of a solution is proportional to its ion concentration
Since charge on ions in solution facilities the conductance of electrical current

30. Conductivity Measurement
Conductivity is measured by
Two plates placed in the sample
Potential is applied across the plates and current is measured
Conductivity (G), the inverse of resistivity (R) is determined from the voltage and current values according to Ohm's law
G = 1/R = I (amps) / E (volts)

31. Conductivity Units Basic unit of conductivity
Siemens (S), formerly called the mho
Cell geometry affects conductivity values
Standardized measurements are expressed in specific conductivity units (S/cm) to compensate for variations in electrode dimensions
Specific conductivity (C) is the product of measured conductivity (G) and the electrode cell constant (L/A)
L: length of the column of liquid between the electrode
A: area of the electrodes
C = G x (L/A)

32. Conductivity of Common Solutions
0.055 µS/cm
1.0 µS/cm
50 µS/cm
53 mS/cm
865 mS/cm
Solution
Absolute pure water
Power plant boiler water
Good city water
Ocean water
31% HNO3

33. Conductivity and Temperature
Conductivity measurements are temperature dependent
The degree to which temperature affects conductivity varies from solution to solution
Calculated using the following formula:
Gt = Gtcal {1 + α(T-Tcal)}
Gt = conductivity at any temp T in °C
Gtcal = conductivity at calibration temp Tcal in °C
α = temperature coefficient of solution at Tcal in °C

34. Conductivity and Temperature
Common alphas (α ) are listed in tables
To determine that a of other solutions
Measure conductivity at a range of temperatures
Graph the change in conductivity versus the change in temperature
Divide the slope of the graph by Gtcal to get α

35. Conductivity and Temperature
Conductivity of a solution typically increases with temp
In moderately and high conductive solutions, this increase can be compensated for
Using a linear equation involving temp coefficient (K)
K= Percent increase in conductivity per degree centigrade
Temp coefficient for the following electrolytes generally fall in the ranges below

36. Conductivity and Temperature

37. Conductivity and Temperature

38. Conductivity is Non-Specific

39. Conductivity Probe فحص how??
2 metals in contact with electrolyte solution
Voltage is applied to electrodes and resulting current that flows btw electrodes is used to determine conductance
Amount of current flowing depends on:
Solution conductivity
Length, surface area, geometry of electrodes

40. Conductivity Probe
Apply an AC Voltage to Two Electrodes of Exact Dimensions
Acids, Bases and Salts (NaCl) Dissolve in Solution and Act as Current Carriers
Current Flow is Directly Proportional to the Total Dissolved Solids in Solution
Physical Dimensions of a Conductivity Electrode are Referred to as the Cell Constant
Cell Constant is Length/Area Relationship
Distance Between Plates = 1.0 cm
Area of Each Plate = 1.0 cm x 1.0 cm
Cell Constant = 1.0 cm-1

41. Cell Constant Cell constant:
Measure of current response of a sensor conductive solution
Due to sensor’s dimensions and geometry
Units: cm-1 (length divided by area)

42. Other Cell Constants
Specific conductivity (C) = Measured conductivity (G) X electrode cell constant (L/A)
L: length of the column of liquid between the electrode
A: area of the electrodes
C = G x (L/A)

44. Four Electrode Conductivity Cells
Measures Current and Voltage Drop
Current Increases with an Increase in Voltage Drop Across Electrodes
Compensates for Minor Coatings on Conductivity Electrodes
Used for Higher Range Measurement V

45. Conductivity vs. pH

46. Total Dissolved Solids
Total dissolved solids (TDS):
Measure of total amount of all materials that are dissolved in water
These materials, both natural and made by humans
Inorganic solids, with a minor amount of organic material
Depending on the type of water, TDS can vary
Seawater contains 3.5% (35,000 mg/L) TDS
EPA Secondary Drinking Water Standards recommends that the TDS concentrations in drinking water not exceed 0.05% (500 mg/L), based on taste and aesthetics

47. Measuring TDS With Conductivity Method
σ = conductivity (μs/cm)
Electrical conductivity of water is directly related to the concentration of dissolved solids in the water
Ions from the dissolved solids in water influence the ability of that water to conduct an electrical current, which can be measured using a conductivity meter
When correlated with laboratory TDS measurements, electrical conductivity can provide an accurate estimate of the TDS concentration

48. Hardness
Waters that contain a significant concentration of dissolved minerals like calcium, magnesium, strontium, iron, and manganese, are called "hard“
Because it takes a large amount of soap to produce a lather or foam with these waters.
Total hardness is expressed as mg/L of calcium carbonate because calcium (Ca) and carbonate (CO3) are dominant ions in most hard waters
The following table gives concentration of CaCO3 dissolved in water by its degree of hardness.
Degree of Hardness
mg/L as CaCO3
Soft
0-60
Moderately Hard
60-120
Hard
Very Hard
Greater than 180

49. Sample Measurements
Rinse the conductivity cell sensing element with DI water between sample
Dip cell up and down in sample 2-3 times to completely wet surface
Allow air bubbles to escape from conductivity cell side holes by tilting cell slightly
It is important to control sample temp
Since reading will continue to drift until the temp has stabilized

50. Storage
1. Best to store conductivity probe so that electrodes are immersed in DI water
2. Can also store dry
Before use:
Probe should be soaked in DI water for minutes
To assure complete wetting of the electrodes

51. Cleaning
1. For most applications, a hot solution of water with mild lab detergent can be used for cleaning
2. Dilute 1% nitric acid may be used followed by DI water rinsing