Lecture 2 Processes and Process Variables

56
Lecture 2 Processes and Process variables 1 Dr. A. Alim

Transcript of Lecture 2 Processes and Process Variables

Page 1: Lecture 2 Processes and Process Variables

Lecture 2

Processes and Process variables

1 Dr. A. Alim

Page 2: Lecture 2 Processes and Process Variables

Processes and Process variables:

Density and Specific gravity

Mass and Volumetric Flow Rate

Moles and Molecular Weight

Concentration

Pressure

Temperature

2

Page 3: Lecture 2 Processes and Process Variables

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

© 2005 by John Wiley & Sons,

Inc. All Rights Reserved

3

Page 4: Lecture 2 Processes and Process Variables

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

Page 5: Lecture 2 Processes and Process Variables

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

Page 6: Lecture 2 Processes and Process Variables

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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Page 7: Lecture 2 Processes and Process Variables

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

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Page 8: Lecture 2 Processes and Process Variables

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

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Page 9: Lecture 2 Processes and Process Variables

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

Page 10: Lecture 2 Processes and Process Variables

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

Page 11: Lecture 2 Processes and Process Variables

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

Page 12: Lecture 2 Processes and Process Variables

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

Page 13: Lecture 2 Processes and Process Variables

• 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

Page 14: Lecture 2 Processes and Process Variables

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

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Page 15: Lecture 2 Processes and Process Variables

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

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Page 16: Lecture 2 Processes and Process Variables

Process Variables – Concentration

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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Page 17: Lecture 2 Processes and Process Variables

Process Variables – Pressure

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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Page 18: Lecture 2 Processes and Process Variables

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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Page 19: Lecture 2 Processes and Process Variables

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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Page 20: Lecture 2 Processes and Process Variables

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

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Page 21: Lecture 2 Processes and Process Variables

The Barometer An instrument to measure atmospheric (barometric) pressure

Material primarily from “Elementary

Principles of Chemical Processes”,

Felder and Rousseau, 3rd ed. , Wiley

2005

© 2005 by John Wiley & Sons,

Inc. All Rights Reserved 21

Page 22: Lecture 2 Processes and Process Variables

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

Page 23: Lecture 2 Processes and Process Variables

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

Page 24: Lecture 2 Processes and Process Variables

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

Page 25: Lecture 2 Processes and Process Variables

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

Page 26: Lecture 2 Processes and Process Variables

IMPORTANT : Only absolute pressure is used in thermodynamic calculations !

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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Page 27: Lecture 2 Processes and Process Variables

IMPORTANT : Only absolute pressure is used in thermodynamic calculations !

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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Gage +ve

Gage –ve

Or Vac.

Abs.

Page 28: Lecture 2 Processes and Process Variables

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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Page 29: Lecture 2 Processes and Process Variables

29 2. Resistance Transducer

3. 1.

Page 30: Lecture 2 Processes and Process Variables

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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Page 31: Lecture 2 Processes and Process Variables

Resistance Transducer

31

Page 32: Lecture 2 Processes and Process Variables

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

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Page 33: Lecture 2 Processes and Process Variables

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

33

Page 34: Lecture 2 Processes and Process Variables

DO NOT FORGET

gC !!!

Material primarily from “Elementary

Principles of Chemical Processes”, Felder

and Rousseau, 3rd ed. , Wiley 2005

© 2005 by John Wiley & Sons, Inc. All Rights Reserved

34

Page 35: Lecture 2 Processes and Process Variables

Material primarily from “Elementary

Principles of Chemical Processes”, Felder

and Rousseau, 3rd ed. , Wiley 2005

© 2005 by John Wiley & Sons,

Inc. All Rights Reserved

35

Manometers: Special Cases

Page 36: Lecture 2 Processes and Process Variables

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

© 2005 by John Wiley & Sons,

Inc. All Rights Reserved

36

Manometers: Special Cases

Page 37: Lecture 2 Processes and Process Variables

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

37

Page 38: Lecture 2 Processes and Process Variables

Material primarily from “Elementary

Principles of Chemical Processes”, Felder

and Rousseau, 3rd ed. , Wiley 2005

© 2005 by John Wiley & Sons,

Inc. All Rights Reserved 38

Page 39: Lecture 2 Processes and Process Variables

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

Page 40: Lecture 2 Processes and Process Variables

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

40

Page 41: Lecture 2 Processes and Process Variables

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

Page 42: Lecture 2 Processes and Process Variables

Material primarily from “Elementary

Principles of Chemical Processes”, Felder

and Rousseau, 3rd ed. , Wiley 2005

© 2005 by John Wiley & Sons,

Inc. All Rights Reserved

42

Page 43: Lecture 2 Processes and Process Variables

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

Page 44: Lecture 2 Processes and Process Variables

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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Page 45: Lecture 2 Processes and Process Variables

Home Work # 1

45

Page 46: Lecture 2 Processes and Process Variables

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

Page 47: Lecture 2 Processes and Process Variables

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

47

Page 48: Lecture 2 Processes and Process Variables

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

Page 49: Lecture 2 Processes and Process Variables

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

Page 50: Lecture 2 Processes and Process Variables

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

Page 51: Lecture 2 Processes and Process Variables

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

Page 52: Lecture 2 Processes and Process Variables

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

Page 53: Lecture 2 Processes and Process Variables

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

Page 54: Lecture 2 Processes and Process Variables

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

Page 55: Lecture 2 Processes and Process Variables

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

Page 56: Lecture 2 Processes and Process Variables

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