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Welcome to Introduction to Chemical Engineering

Name: Greg Griffin

Room: Opposite School OfficeEmail: gregory.griffin@nu.edu.kz

Assistant: Mereke Tontayeva

6 weeks duration (weeks 2 7) 5 weeks of lectorials (3hrs Tuesday/

1hr Thursday) 1 assessable tute question/week (1%

each) Expectation that you will attempt all

tutorial questions. Solutions are provided at the end of the

week. 1 week (week 7) - 2 hr mid-semester

test (70% of final grade) Sample test with solutions will be

distributed prior to week 7.

This course the basicsMy Part

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Consultation times I have a relaxed open door policy if you are struggling with understanding the content or answering the tutorial questions then come and see me.

Prescribed text - Elementary Principles of Chemical Processes, 3rd Edition, R M Felder and R W Rousseau, John Wiley and Sons, 2005.

This course the basicsMy Part

Introduction to Chemical Engineering Week 2

Units

Almost all numerical quantities has a unit associated with them.

There are 50 students enrolled in this course

eg

Units are necessary to make the number meaningful.

Note: Your tutorial & test solutions should always contain the correct units!

Number

Unit

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Dimensions

Basic building blocks of measurement

Properties that can be measured

Length

Temperature

Mass

Time

Density

Student number (Number of students)

Units Ways of expressing dimensions.

Questions: What is my mass?

Dimension

Answer: My mass is 72 kgNumber Unit (gives number a meaning)

or My mass is 72,000 g

or My mass is 158 lb

gram

pound

Conversion

For every dimension, there are lots of number/unit combinations. Getting the right combination is very important.

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The Mars Probe A cautionary tale

Mars

Mars Climate Orbiter

Rocket thrusters control flight path.

Calculation for Thrust given in pound-force (American Engineering).

NASA engineers thought thrust was in Newtons (SI).

Actual Orbit

Ouch!!

Intended Orbit

Systems of Units

Many of these exist:

SI* (or Systme International) Otherwise known as the metric system.

American Engineering*

British Engineering

cgs

fps or English absolute

*Most common systems

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Why SI is such a nice unit system

Calculate the kinetic energy of a 4kg particle traveling at 5 m/s

eg

SI Unit

KE = mv

= (4 kg) (5 m/s)

= 50 kg m/s

= 50 J

Note: 1 J = 1 kg m/s

SI. Unit for energy

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What is the weight of a 5.0 kg body at the earths surface?

W = mg

= (5.0 kg) (9.81 m/s)

= 49 kg m/s

= 49 N

Gravitational constant

S.I unit

S.I Unit for force.

An electrical current, 9A, flows across a voltage drop of 10V. What is the power dissipated in this process?

S.I unit

P = VI

= (10V) (9A)

= 90 VA

= 90 W

S.I unit

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Why the American Engineering system is not so nice:

What is the kinetic energy of a 4.0 lb particle traveling at 5.0 ft/s.

A.E. Units

KE = (4.0lb) (5.0 ft/s)

= 50 lb ft/s

50 Btu or 50hp.hr

To convert 50 lb ft/s to Btu or hp.hr, need to know conversion

What is the weight of a 5.0 lb body at the earths surface?

W = mg

= (5.0 lb) (32.2 ft/s)

= 161 lb.ft/s

161 lbf

A.E. units

pound force.

32.2 lb.ft/s = 1 lbf

1 lbm weighs 1 lbf at the earths surface

pound mass

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Other reasons S.I is more convenient than A.E

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Trick Question

What is heavier.

An ounce of gold or an ounce of feathers?

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Examples:

4 kg of water flows through a pipe at 25 ft/s.

What is the kinetic energy of the water in

a) Joules

b) ft.(lbf)

a) KE = mv2

= () (4 kg) (25 ft/s)2

= 1250 kg ft2/s2

1 ft = 0.3048 m

b)

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Another Example:

A oil blow out in Mexico Gulf was reported to discharge 30,000 bbl of oil per day.

Barrels still the most common unit used for oil quantities

If the oil slick is mi wide and 1 in. thick, how much does the slick grow each day ( in km)?Data: 1 bbl = 42 US gal

1 US gal = 0.1337 ft3

1 mi = 1.61 km.

Solve in class

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Another example:

Air cannot be used for diving at depths of greater than 150 ft because of nitrogens narcotic effects. Divers cite the Martini Law: Every 50 ft of depth is equivalent to drinking one martini.

A depth of 1000 ft is equivalent to how many:

a) Martinis

b) lbf /ft2

c) Newtons/m2 (or Pascal, Pa)

Sea water has a density of 63.9 lb/ft3

Solve in class

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Tutorial time Complete question 1 from tutorial sheet

Another Example

Does 0.943 have a unit?

h = heat transfer coefficient

[=] Btu/hr.ft2 F

k = thermal conductivity

[=] Btu/hr.ft F

= density

[=] lb/ft3= viscosity

[=] lb/hr. ft

= enthalpy

[=] Btu/lb

L = length

[=] ft

G = gravitational constant

[=] ft/hr2

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Solution:

Ignore the numbers, consider only the units.

Let 0.943 [=]

(0.943) is dimensionless

Dimensional Homogeneity

Engineering equations contain many variables (almost always).

For Consistency:

Dimensions on both sides of = must be same

Added/subtracted elements must have the same dimensions.

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Example

Van Der Waals Equation:

Must have same units

Must have the same units Must have the same units

What are the units of a and b?

(V- b) =

Must have same units

b has units of m3/mol

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What is the units of c

L.H.S of equation:

R.H.S. of equation:

Units Used Affect Constants

Example:

Simple equation for heat transfer from a pipe to air is:

h = heat transfer coefficient, Btu/hr.ft2.F

G = mass flow rate, lbm/hr.ft2

D = outside diameter of pipe, ft.

What are units of 0.026?

What is the SI equivalent of the equation?

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Note that there are functions of variables that must be dimensionless.

eg x = et

t [=] hr

x [] ehr

Similarly for the functions

sin(x) arcsin(x) ax

cos(x) : ex

tan(x) : :

ln(x) : :

log(x)

f(x) is dimensionless.

Example:

The volume of a microbial culture is observed to increase according to the formula:

V = et

Where V [=] cm3

t [=] s

Calculate a new equation where:

V [=] in3

t [=] hr

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Now, we write

V = a ebt

Where: b = 1 s-1

a = 1 cm3

bt is dimensionless

ebt is dimensionless

aebt [=] cm3 [=] V

Now, if V [=] in3

t [=] hr

then for consistency:

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Dimensionless Groups

In engineering, you will be exposed to a number of Dimensionless Groups that have physical significance.

For example:

= Density [=] kg/m3

v = velocity [=] m/s

D = Diameter of pipe [=] m

= viscosity [=] kg/m.s

SI. units

[=] lb/ft3

v [=] ft/s

D [=] ft

[=] lb/ft.s

Note: If the A.E. system is used

Dimensionless

Dimensionless

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Dimensionless groups are always dimensionless as long as a consistent unit system is used.

Example: You are given the following data for the properties of a polymer melt. It is desired to pump this material in laminar flow (Re < 2100) through a pipe of 1 inch diameter.

What is the maximum allowable velocity in the pipe? (in m/s)

Data: = 1.5 g/cm3

= 10.0 centipoise (cp)

Method 1: Convert all dimensions to SI.

1 g/cm3 = 1000 kg/m3

1 centipoise = 10-2 poise

1 poise = 10-1 kg/m.s

1 inch = 2.54 cm = 2.54 10-2 m

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1 inch = 2.54 10-2 m

For laminar flow;Method 2

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Tutorial time Complete question 6 from tutorial sheet Another example:

The Prandtl number, Pr, is an important dimensionless group used in heat transfer calculations.

Where: CP = Heat capacity (J/kgC)

= viscosity (kg/m.s) in SI.

k = Thermal conductivity (W/m.k) in SI.

If: CP = 0.583 J/g.C

= 1936 lb/ft.hr

k = 0.286 w/m.C(W/m.k) in SI.

Calculate Pr.

In SI units

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Solution: Process Variables

In all processes, whether they are chemical or environmental in nature, there are a series of operations where an objective is accomplished.

Process

Process operations or unit operations

Inputs

FeedOutputs

Products

Process Streams

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Need to analyse the performance of a unit operation. Need to control a unit operation.

ie - How well does it work?

- Given the inputs, what is the output?

- Given a desired output?what are the inputs?

- What are the waste?Can these be reduced?

To answer these questions, we need to be able to measure or calculate important process variables.

Example:

A large scale North Queensland industry

The Home Brew KitT P A single unit

operations

Ethanol Water Flavour

FlavourWaterSugarMaltYeast

This is a Batch process

- The vessel is charged or filled with reactants

- The reaction (fermentation) occurs

- The product is removed.

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Important variables to consider.

Mass and Volume of the materials

If the wrong amounts are added then the product beer will not taste right.

Flow Rate

For continuous processes, important to know rate of addition of materials.

Chemical Composition- How strong do you want your beer?Full Strength? Light?

- Ethanol concentration.

Temperature

- If the fermentation occurs at too high a temperature, the yeast dies (no product)

- If the temperature is too low, fermentation is too slow, long time for product to form.

Pressure

- Fermentation produces CO2 (carbon dioxide) gas

- Causes pressure to rise

- If pressure too high, vessel will burst

- If pressure is too low, outside feral yeast can enter.

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Note that most of these variables are important in environmental processes.

Example:

A lake

Flow Rate: How much water enters and leaves the lake?

- Low water flow causes stagnation, poor water quality

Chemical Composition:What is the salinity? pH? Concentration of toxins?

Temperature

- How hot is the lake?

- Too hot and the aquatic life dies (or thrives!)

Mass and Volume

- How large is the lake?

- How much solids are suspended in the water (turbidity)

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Density ()

- Mass/Volume of a substance (g/cm3 very common, kg/m3 SIlb/ft3 A.E.)

Specific Volume

- Volume/Mass of a substance

- Inverse of density.

Mass

Volume

Volume

mass

Specific Gravity

- Ratio of density to a reference density.

Density of material

Density of reference material

A common reference density is water at 4C.

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Density of solids + liquids vary little with temperature and pressure.

Where temperature is important, SG is quoted with material and reference temperature.

Example:

Measured material at 20C.

Reference material at 4C

= 0.73 1.000 g/cm3

= 0.73 g/cm3 at 20C

Flow Rate

Material is transferred from unit operation to unit operation.

Important to measure Flow Rate

- Mass flow rate (mass/time)

- Volumetric flow rate (volume/time)

The two flows are linked:

Dot signifies flow rate

Volumetric flow rateMass flow rate

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Usually, want to know mass flow rate, but traditional flow meters tend to read off volumetric flow.

P Pipe

In an orifice meter:Velocity

Cross sectional area of the pipe

Float

Glass tube

Rotameters

Open area around float

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Example:

Liquid benzene, an organic liquid, and n-hexane are blended to form a stream flowing at a rate of 700 lb/hr. The density of the combined stream is 0.85 g/cm3.

What are the flow rates of the benzene and n-hexane? (in ft3/hr)

Now

Assume:

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From _____ 2

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Tutorial time Complete question 3.6 from prescribed text Pressure

Pressure is ratio of Force to Areaupon which it is acting.

Fluid Pressure

Pressure on walls in a pipe in which fluid is flowing.

F

Area

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Hydrostatic Pressure

- Pressure due to weight of fluid.

- Consider a tank filled with liquid.

Pressure of atmosphere = Patm

Area = A

hFluid, density

Volume of tank = V = hA

Weight of fluid in tank = mg= Vg= Ahg

Now, total force exerted downwards at base of tank is:

Weight of atmosphere Weight of fluid in tank

Pressure at base of tank is

Atmospheric pressure can vary, but a standard atmospheric pressure is defined:

1 atm = 101325 Pa= 14.7 p.s.i.

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Absolute and Gauge Pressure

When quoting pressures, two different zero points are commonly used.

a) Absolute pressure 0 pressure is a perfect vacuum.

b) Gauge pressure 0 pressure is 1 atm pressure.

Patm

Perfect Vacuum

Pressure

Absolute Pressure Gauge

Pressure

Pabsolute = Patm + Pgauge

Commonly we will see gauge or absolute pressures denoted by the addition of g or a to the quoted pressure.

eg

50 psia

or

35.3 psig

absolute

gauge

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Example:

The great molasses disaster of 1919, Boston.

In 1919, a storage tank containing molasses burst in Boston releasing a wave of molasses down the city streets. Some 2.3 million gallons (US) of molasses was spilt resulting in the death of 21 people.

Data: Height of storage tank = 30 ft

SG (molasses) = 1.4

Calculate:

(i) The mass (in lbs) of molasses spilt.

(ii) The absolute and gauge pressure at the bottom of the tank (lbf /in2)

Solution:

2.3 million US gallons of molasses30 ft

Molasses Tank

Assume atmospheric pressure = 1 atm

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Example: (Cont.)

Absolute Pressure = Patm + gh

Assume Patm = 1 atm

= 14.7 p.s.i.

Absolute pressure = 14.7 + 18.2

= 32.9 psia

Gauge pressure = 18.2 psig

PgaugePabsolute

Atmospheric Pressure

Negative Pgaugeor Vacuum.

~ 1 atm

Note: Pgauge can be negative. Pabsolute is always positive vacuum is some times used to described negative Pgauge.

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For Example: Manometers and Head of Fluid

Manometer

gas

PipeOrifice

Liquid

P1P2

P2h P = gh

P1P1

Gravity

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If mercury is used in manometer:

1 atm = 760 mm Hg (at 0C)

or water = 10.333 m H2O (at 4C)

= 33.9 ft H2O (at 4C)

Chemical symbol for mercury

{Head of fluid

Open end manometer:

Patm

Patmh P1 - Patm = gh

P1

Pipe P1

Closed end manometer:

Sealed end -evacuated

P2 = 0 (absolute)h

P1 = gh

P1

Pipe

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Example:

Two mercury Manometers, one open-end and the other closed end, are attached to an air duct.

The reading on the open-end Manometer is 25 mm and that on the closed end Manometer is 800 mm.

Determine Pgauge, Pabsolute, PATMNow from the open end Manometer:

Now closed-end Manometer

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Temperature

- An important physical variable

- Effects what phase a material is (solid, liquid, gas)

- Is a measure of the average kinetic energy of constituent molecules/atoms in material

- Effects rate of reaction and extent of reaction.

Four Main Temperature Scales.

Celsius Scale

Fahrenheit Scale

0C

32F

100C

180F

100C

212F

Freezing point of water at 1 atm Pressure

Boiling point of water at 1 atm Pressure

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Kelvin (K)

Rankine Scale (R)

0 K

0R

273.15 K

491.67 R

373.15 K

Absolute zero (no energy)

Boiling point of water at 1 atm

Pressure

Freezing Point of water at 1 atm

ABSOLUTE SCALES

671.67 R

Example:

Convert 50C into F, R, K.

T(K) = T(C) + 273.15

T(K) = 50 + 273

= 323 K

T(F) = 1.8T(C) + 32

= 1.8 50 + 32

= 122 F

T(R) = T(F) + 460

= 122 + 460

= 582 R

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Composition and Concentration

Mixtures of chemical and their chemical composition can be described in a number of ways:

Mass and mole fractions are converted to % by multiplying by 100.

Note: If a composition is quoted in % without referring to whether it is mole of mass % then:

Liquid or Solid Mass%

Gas Mole%

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Eg.

An alcoholic beverage is said to contain 9.5 mass% ethanol (C2H5OH), 4.6 mass% glucose (C6H12O6) and 85.9 mass% water (H2O).

i) What is the average molecular mass of the beverage?

ii) What volume% of alcohol is in the beverage?

i) Let us assume we have 100 gm of beverage.

Basis

9.5 gm of EtOH (ethanol)

MW(EtOH) = 2 12.0 + 6 1.0+ 1 16.0

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Concentration

Most chemicals in both nature and during processing are diluted to some extent. We call the component in solution the solute.

- Orange juice/cordial (diluted in water)

- Fuel additive (diluted with petrol/oil)

- Pollutants (PCBs in water, VOCs in air).

Concentrations are expressed as ratio of solute to total solution.

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Some concentration units:

g/L Mass concentration

mole/L molarity (or molar)

ppm parts per million

ppb parts per billion.

Mass fraction for liquids/solids

Mole fraction for gases.

Molality (or molal) mols solute/1000g of solvent.

Example:

An aqueous 0.50 molar solution of sulphuric acid (H2SO4) flows into a process at 1.25 m3/min. If the S.G. of the solution is 1.03, calculate:

i) The mass concentration of H2SO4 in kg/m3.

ii) The mass flow rate of H2SO4 in kg/s.

iii) The mass fraction of H2SO4.

iv) In ppm?

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