lecture 2 processes and process variables
TRANSCRIPT
Lecture 2
Processes and Process variables
1 Dr. A. Alim
Processes and Process variables:
Density and Specific gravity
Mass and Volumetric Flow Rate
Moles and Molecular Weight
Concentration
Pressure
Temperature
2
Process Variables – Density and Specific Gravity
Summary:
Density (ρ) = Mass / Volume
Specific gravity (solids and liquids) = Density / Density of water
Specific gravity (gases) = Density / Density of air
Question: what are examples of units for density and for
specific gravity?
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
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Inc. All Rights Reserved
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Material primarily from “Elementary
Principles of Chemical Processes”,
Felder and Rousseau, 3rd ed. , Wiley
2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
4
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
5
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
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Inc. All Rights Reserved
6
Process Variables – Mass and Volumetric
Flow Rate Measurements
Material primarily from “Elementary
Principles of Chemical Processes”,
Felder and Rousseau, 3rd ed. , Wiley
2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
7
Process Variables – Moles and Molecular
Weight
A more accurate definition of atomic weight :
A dimensionless ratio of the average atomic mass (average of all present isotopes) to
1/12 the atomic mass of carbon -12
Note that “weight” here does not mean the usual definition of “weight” as the force exerted
by gravity we discussed earlier.
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
8
Material primarily from
“Elementary Principles
of Chemical Processes”,
Felder and Rousseau,
3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
9
Process Variables – Moles and Molecular
Weight
Material primarily from
“Elementary Principles
of Chemical Processes”,
Felder and Rousseau,
3rd ed. , Wiley 2005 © 2005 by John Wiley & Sons,
Inc. All Rights Reserved
10
Material primarily from
“Elementary Principles
of Chemical Processes”,
Felder and Rousseau,
3rd ed. , Wiley 2005 © 2005 by John Wiley & Sons,
Inc. All Rights Reserved
11
Material primarily from “Elementary
Principles of Chemical Processes”,
Felder and Rousseau, 3rd ed. , Wiley
2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
12
• What is the average molecular weight :
From equation 3.3-7:
Av mol weight = (0.15)(32) + (0.044)(28) + (0.12)(44) + (0.69)(28) = 30.5
From equation 3.3-8:
Av mol weight = 1/[0.16/32 + 0.04/28 + 0.17/44 + 0.63/28] = 30.5
Or simply:
Av mol weight = total mass / total moles = 100 / 3.279 = 30.5
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
13
Mole fraction-Mass fraction- Volume fraction:
The process for converting mass fraction to mole fraction and vice versa can
Also be extended to include conversions to and from volume fractions.
Key equation for each material is : volume = mass/density
Example:
A mixture of A and B has 30% by mass of A (sp.gravity 0.6) and the rest is B
(sp. Gravity 0.7). What are the volume fractions of A and B in the mixture?
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
14
Mole fraction-Mass fraction- Volume fraction:
The process for converting mass fraction to mole fraction and vice versa can
Also be extended to include conversions to and from volume fractions.
Key equation for each material is : volume = mass/density
Example:
A mixture of A and B has 30% by mass of A (sp.gravity 0.6) and the rest is B
(sp. Gravity 0.7). What are the volume fractions of A and B in the mixture?
Basis 100 grams of mixture:
Material Mass (g) density(g/cm3) volume(cm3) Volume fraction
A 30 0.6 50 50/100 = 0.33
B 70 0.7 100 100/150 = 0.67
Total 100 150
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
15
Process Variables – Concentration
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
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Inc. All Rights Reserved
16
Process Variables – Pressure
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
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Inc. All Rights Reserved
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Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
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Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
19
Pressure as Fluid head
• In addition to being expressed as force per unit area, a
pressure may also be expressed as head of a particular fluid.
• This is the equivalent height of a hypothetical column of this
fluid that would exert the given pressure at its base if the
pressure at the top were zero.
• With P0 = 0 , we can write P = ρ. h . (g/gc)
• Therefore Ph = h = (P. gc) / (ρ . g)
Material primarily from “Elementary
Principles of Chemical Processes”,
Felder and Rousseau, 3rd ed. , Wiley
2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
20
The Barometer An instrument to measure atmospheric (barometric) pressure
Material primarily from “Elementary
Principles of Chemical Processes”,
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2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved 21
Pressure - is the ratio of force to the area on which the force acts; has
dimensions of (Force/length2)
Units in SI system = N/m2 or Pascal (Pa)
Units in CGS system = dynes/cm2
Units in British system = Ibf/ft2 (psf), or more commonly Ibf/in
2 (psi)
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
22
The Bar:
The Bar is a widely used metric unit of measurement for pressure and 1
bar equals precisely 100,000 Pascals. Even though Bar is not an SI unit it
has been adopted as one of the most popular pressure units particularly
in European countries where most pressure measurement instruments
are specified with pressure ranges in bar.
The value of 1 bar is a close approximation to atmospheric pressure and
is often used to represent atmospheric pressure rather than standard
atmosphere (101325 Pascals) which is the correct value used by the
scientific and engineering community.
Material primarily from
“Elementary Principles
of Chemical Processes”,
Felder and Rousseau,
3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
23
Material primarily from
“Elementary Principles
of Chemical Processes”,
Felder and Rousseau,
3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
24
Material primarily from
“Elementary Principles
of Chemical Processes”,
Felder and Rousseau,
3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
25
IMPORTANT : Only absolute pressure is used in thermodynamic calculations !
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
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Inc. All Rights Reserved
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IMPORTANT : Only absolute pressure is used in thermodynamic calculations !
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
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Inc. All Rights Reserved
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Gage +ve
Gage –ve
Or Vac.
Abs.
Fluid Pressure Measurements
• Elastic elements methods - Bourdon
gauge
• Liquid column methods – Manometers
• Electrical methods – strain gauges,
transducers
Material primarily from
“Elementary Principles
of Chemical Processes”,
Felder and Rousseau,
3rd ed. , Wiley 2005 © 2005 by John Wiley & Sons,
Inc. All Rights Reserved
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29 2. Resistance Transducer
3. 1.
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
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Resistance Transducer
31
The Manometer
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
32
The Manometer
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
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33
DO NOT FORGET
gC !!!
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
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Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
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Inc. All Rights Reserved
35
Manometers: Special Cases
Note: For gases, you may assume the gas density is zero
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
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Inc. All Rights Reserved
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Manometers: Special Cases
IMPORTANT : Pressure difference does not depend on manometer shape
diameter, inclination,…etc.
The ONLY important factor is the vertical distance between fluid surfaces.
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
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Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
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Inc. All Rights Reserved 38
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
39
Process Variables – Temperature
• Is a measure of the average molecular
kinetic energy.
• Measurements:
Thermometers (Liquid expansion)
Thermocouples (Resistance)
Pyrometers (Radiation)
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
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Industrial thermometer
Pyrometer
Thermocouples
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005 © 2005 by John Wiley & Sons, Inc. All Rights Reserved
41
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
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Inc. All Rights Reserved
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Temperature conversion Temperature Interval conversion
Example: Water freezes at 0 oC which is the same as 1.8X0 + 32 = 32 oF
Example: The gas constant R is 1.987 cal/g mole K. Convert into Btu/lb mole oR. R = (1.987 cal/g mole K).(1Btu/252 cal) .(454 g mole/1 lb mole).(1 K/1.8 oR) = 1.987 Btu/lb mole oR.
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
43
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
44
Home Work # 1
45
Home Work # 1
Thursday, June 7, 2012
Problems:
2.1 page 31
2.2 page 31
2.3 page 31
2.6 page 31
2.7 page 32
2.8 page 32
2.9 page 32
2.10 page 32
2.25 page 35
Example 2.5-2 page 19
2.18 page 33
2.31 page 36
2.45 page 41 (parts a, b, and c only)
3.6 page 65
3.16 page 68
3.25 page 69
3.36 page 73
3.41 page 74
3.42 page 74
3.48 page 77
3.46 page 76
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
46
Solutions
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
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Material primarily from
“Elementary Principles
of Chemical Processes”,
Felder and Rousseau,
3rd ed. , Wiley 2005 © 2005 by John Wiley & Sons,
Inc. All Rights Reserved
48
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
49
Material primarily from
“Elementary Principles
of Chemical Processes”,
Felder and Rousseau,
3rd ed. , Wiley 2005 © 2005 by John Wiley & Sons,
Inc. All Rights Reserved
50
Material primarily from
“Elementary Principles
of Chemical Processes”,
Felder and Rousseau,
3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
51
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
52
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
53
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
54
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
55
Material primarily from “Elementary
Principles of Chemical Processes”, Felder
and Rousseau, 3rd ed. , Wiley 2005
© 2005 by John Wiley & Sons,
Inc. All Rights Reserved
56