1. Chemical processes I LECTURER Dr. Riham Hazzaa
TEXTBOOK R.M. Felder and R.W. Rousseau “ Elementary Principles of Chemical Processes”, John Wiley & Sons, 3rd Edition 2005.

2. Dimensions, Units, and Unit Conversion
“Every physical quantity can be expressed as a product of a pure number and a unit, where the unit is a selected reference quantity in terms of which all quantities of the same kind can be expressed”
Physical Quantities
• Fundamental quantities
• Derived quantities
Dr.Riham Hazzaa

3. Fundamental Quantities
Length
Mass
Time
Temperature
Amount of substance
Electric current
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4. • Area [Length × length or (length)2] • Volume [(Length) 3]
Derived Quantities
• Area [Length × length or (length)2]
• Volume [(Length) 3]
• Density [Mass/volume or mass/ (length) 3]
• Velocity [Length/time]
• Acceleration [Velocity/time or length/ (time) 2]
• Force [Mass × acceleration or (mass × length)/ (time) 2]
Dr.Riham Hazzaa

5. Value Unit Dimension 110 mg mass 24 hand length 5 gal volume (length3)
110 mg of sodium
24 hands high
5 gal of gasoline
Value
Unit
Dimension
110 mg
mass 24
hand
length 5
gal
volume (length3)
Dr.Riham Hazzaa

6. Dimension :A property that can be measured directly (e. g
Dimension :A property that can be measured directly (e.g., length (L), mass (M), time (t), temperature (T)) or calculated, by multiplying or dividing with other dimensions (e.g., volume, velocity, force)
Unit: A specific numerical value of dimension. "Units" can be counted or measured. Many different units can be used for a single dimension, as inches, miles, centimeters are all units used to measure the dimension length.
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7. SYSTEMS OF UNITS
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8. Every system of units has:
A set of "basic units" for the dimensions of mass, length, time, absolute temperature, electric current, and amount of substance.
Derived units, which are special combinations of units or units used to describe combination dimensions (energy, force, volume, etc.) For example:
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9. Derived SI Units
The unit for Force can be expressed in terms of the derived unit (newton) or in base units (kg.m/s2)
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10. Multiple units, which are multiples or fractions of the basic units used for convenience (years instead of seconds, kilometers instead of meters, etc.).
the base unit is second, the multiple units of time:
Minutes = seconds
Hour = seconds
Day = second.
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11. Acceleration (a) V/t = L/t2
Examples of the Dimensions of Derived Quantities
Area (A) A = L×L=L2
Volume (V) V = L×L×L=L3
Density (ρ) ρ = M/V=M/L3
Velocity (V) V = L/t
Acceleration (a) V/t = L/t2
Dr.Riham Hazzaa

12. What is the dimension of P?
Pressure (P ) is defined as “the amount of force (F ) exerted onto the area (A)
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13. Unit of pressure (P), in SI system, kg/m.s2 N/m2
“Pascal (Pa)”, which is defined as
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14. Example: Determine the units of density, in c gs, SI, and AE systems?
cgs unit system is g/cm3
SI unit system is Kg/m3
AE unit system is 1bm/ft3
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15. This is defined as follow:
CONVERSION OF UNITS
To convert units from one system to another, we simply multiply the old unit with a conversion factor.
This is defined as follow:
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16. EXAMPLE 1 Convert 10 m/s to ft/s. 1 m is equal to 3.28 ft.
The conversion factor is 3.281ft/m
Dr.Riham Hazzaa

17. EXAMPLE 2 Convert 10 m2/s to ft2/s. The conversion factor is
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18. EXAMPLE 3 Convert 10 kg m/s2 to lb ft/min2 1 kg = 2.2 lb 1m = 3.28 ft
60 s = 1 min
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19. EXAMPLE 5 Convert the mass flux of 0. 04g/m
EXAMPLE 5 Convert the mass flux of 0.04g/m.min2 to that in the unit of lbm/h ft2
= 4.92 × 10-4 lbm/h ft2
Dr.Riham Hazzaa

20. EXAMPLE 6 Convert 23 1bm ft/ min2 to its equivalent in kg.cm/s2
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21. EXAMPLE 7
At 4 oC, water has a density of 1 g/cm3. Liquid A has a density at the same temperature of 60 lbm/ft3. When water is mixed with liquid A, which one is on the upper layer?
Dr.Riham Hazzaa

22. Force & Weight
force (F) is the product of mass (m) and its acceleration (m)
F=ma
its corresponding units:
"Pound-force" (lbf),
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23. The force in newtons required to accelerate a mass of 4 kg at a rate of 9 m/s2 is
The force in lbf required to accelerate a mass of 4 lbm at a rate of 9 ft/s2 is
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24. The conversion between the defined unit of force (N, dyne, lbf) and natural units is so commonly used that we give it a special name and symbol, gc.
g/ gc = N/kg
g/ gc = dyne/g
g/ gc = 1 lbf/lbm
Dr.Riham Hazzaa

25. Weight
Weight is defined to be the force exerted on an object by gravity, so an object of mass m subjected to the gravitational acceleration g, will have weight
W = mg/gc
For example, the mass of a steel ball is 10 kg. The weight of this ball on the earth’s surface is:
W = 10 Kg x 9.81 N/kg = 98.1 N
g/ gc = N/kg
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26. W(lbf) = 124.8 lbm g/gc (lbf/lbm)
Example: Water has a density of bm/ft3. How much does 2 ft3 of water weigh
(1) at sea level and 45◦ latitude
(2) in Denever, Colorado, where the altitude is 574 ft and the gravitational acceleration is ft/s2
The mass of the water is
The weight of water is
W(lbf) = lbm g/gc (lbf/lbm)
At sea level, g= ft/s2, g/gc=1 lbf/lbm
W= bf
In Denver, g = , g/gc=32.139/ lbf/lbm
W= bf
Dr.Riham Hazzaa

27. DIMENSIONAL HOMOGENEITY
When adding or subtracting values, the units of each value must be similar to be valid.
EXAMPLE
A (m) =2 B(s)+5
What should the units for constants 2 and 5 have to be for the equation to be valid?
Dr.Riham Hazzaa

28. DIMENSIONLESS QUANTITIES
An example of a dimensionless quantity is Reynold’s number NRe.
This describes the ratio of inertial forces to viscous forces (or convective momentum transport to molecular momentum transport) in a flowing fluid. It thus serves to indicate the degree of turbulence. Low Reynolds numbers mean the fluid flows in "lamina" (layers), while high values mean the flow has many turbulent eddies.
Dr.Riham Hazzaa

29. A quantity k depends on the temperature in the following manner:
The units of the quantity 20,000 are cal/mol, and T is in K (kelvin). What are the units of and 1.987?
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30. Dr.Riham Hazzaa