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```					UEET 101 Introduction to Engineering

Nanotechnology
in
Mechanical Engineering
Presented By
Professor
Department of Mechanical Engineering
Northern Illinois University
DeKalb, IL 60115
1
Outline of the Presentation

   Lecture
   In-class group activities
   Homework

2
Lecture – II: Outline
Nano-Mechanics
Classical Mechanics Assumptions
Material Mechanical Properties
Nanoscale Thermal Phenomena
- Basics of Heat Transfer
- Thermal Conductivity
- Heat Transfer Coefficients

3
Nanomechanics
   Classical theories
   Structure – Property relations
   Stress-strain relations
   Mechanical properties
   Issues in nanomechanics
   Mechanics of nanotubes

4
Classical Mechanics: Assumptions
 Solid is assumed as homogeneous
 Smallest material element has macroscopic properties

 Involves only mechanical forces such as inertia, gravity
and friction
 Motion is uniquely determined by forces - given by
Newton’ s law of motion
 Total Energy = Internal Energy+Kinetic Energy

+ Potential Energy
 Single phase – no phase transformation
5
Basics of Classical Mechanics
Mechanical Behavior of Materials:
Material’s response to applied and residual forces
Deformation:
• When a material is subjected forces, its atoms may be
displaced from their equilibrium position.
• Any separation or displacement from the equilibrium position
requires energy, which is supplied by the force.
- As a material is stretched, atoms tend to separate and
brings attractive forces into play.
- As a material is compressed, atoms tend to come together
and causes repulsion

6
Elastic Deformation: Atoms resumes back to the original
position when imposed forces are released – represents the
relative resilience of the materials.

Plastic Deformation: When a material exceeds the elastic
capability (elastic limit) to restore back to equilibrium position
as the imposed forces are released - the deformation is
permanent.

Engineering Strain:
It is the deformation
l
defined as the ratio of                            l

the dimensional change             l
to the original
l  l
dimension.            Extensional Strain
7
Shear Strain:
This is the deformation of a material between two parallel
plane through a certain angle when subjected to tangential or
shear forces.
- Shear strain is defined as the displacement to the distance
between the planes:
Shear Force
x
x
   tan 
h                     
h

Poisson’s Ratio
Defined as the ratio of strain in     x        y
x-direction to the strain in y-  
direction and expressed as
y       P               P
x

8
Stress:
• Stress is the internal response or resistance that a material
creates when exposed to some kind of external force.
• This internal resistance is due to the inter-atomic attractive
and repulsive forces.
• Displacement in either direction produces an increase in
the force (tensile or Compression) that oppose the
deformation

F                         F                          F

Defined based on balance of       Where
 = Average stress (Internal
external force with the         F
internal resistance force as    resistance force per unit area)
A F = External load or force
A = Cross-sectional area over which
9
the force acts
Hooks’s Law ( Macroscopic Constitutive
Relation or Stress-strain relation)
Defines the proportional relation between the
stress and strain for material below the elastic
limit as   E        = Linear relation
Where E = Modulus of Elasticity (Young’s Modulus)
•Elastic modulus (E) is a measure of the stiffness of the
engineering material
• A higher values of E results in a smaller elastic strains – smaller
the response of the material structure to imposed load
• This is an important parameter for design and analysis in the
estimation of allowable displacements and deflection of a
component or structure
10
Modulus of Rigidity (G)
The modulus of rigidity is the modulus of
elasticity in shear (Relation between shear stress
and shear strain) and defined as   G

Values of G is usually determined by torsion
testing and related to E by the relation
E
G
2(1   )

11
Tensile Strength
Yield Strength (Point-C)
Stress required to produce a
small amount of plastic
deformation
Ultimate Strength (Point –
D)
Maximum stress that a
material can withstand under
the condition of uniaxial
- undergoes substantial
plastic deformation
- not often used for designing
a component                       12
Beam Deformation for Different
Materials
•Many materials are not
strength limited, but
Steel
modulus limited

Titanium
•In some applications,
m          we need material of
high modulus of
elasticity rather than
Aluminum
high strength
•These structure may
not fail if low modulus
Higher the modulus of elasticity     of elasticity is used
lower is the deformation
•It, however, may reach
too much of deflection13
Typical Material Properties
Material      Elastic   Shear     Tension     Possson’sratio
Modulus (E) Modulus    Yield
(GPa)     (GPa)      (MPa)

Aluminum
Alloy            72.4      27.6    504             0.31

Steel-
Low Carbon      207.0      75.9     140            0.33

SS -304         193.2      65.6    960-1450        0.28

Titanium       110.5      44.8      1035           0.31
Silcon Carbide 469.2
Polycarbonate 3.4
SWNT            0.191(TPa) 0.45 TPa                 0.18
14
Breakdown of Continuum Concepts-
Thresholds of Micromechanics
Macromechanics:                                Force, stress
balance/equilibrium
Stress
Constitutive relation:
10   23
atoms   Strain           Hooks law – linear
Area/volume      Classical thermodynamics
Scale:  10 3 m
Micromechanics
Force/surface energy
Structure     balance
Interface     Constitutive relation:
1011 atoms                       nonlinear
Structure property
Scale:  106 m              Phases        relation
Breakdown of Continuum Concepts-
Thresholds of Micromechanics
Nanomechanics:                       Force/energy/structure
Molecule   balance
Atoms      Constitutive relation: ??
10 2 atoms
Quantum    Molecular mechanics
effects
Scale:    10 9 m       energies
Structure property
relation: ??

16
Structure – Property Relations
Nano             Macro
Inter-molecular      Strength
interaction

Bond rotation/       Modulus
angle/strength

Chemical sequence    Viscosity/conductivity
Nanotube diameter/   density/toughness/
Nanotube l/d ratio   dielectric/plasticity

17
Nano-scale Science Hierarchy
Average material properties:
- Surface effects vs volume average
- Molecular network homgenization
- Electromechanical interactions
Nano-scale laws
- Application of classical mechanics law
- New and coupling forces
- Properties/energy depend on molecular structure
- Role of quantum effects

18
Nanomechanics
   Nanomechanics vs. molecular mechanics
   Structure – property relations and dependencies
   Scaling analysis of molecuar structures
   Reliability of characterization techniques at
nano-scale – what are to be measured?

19
Issues in Nanomechanics
Nano-Materials Science
Approaches- top down
- Nanotubes purity
-Continuum models for NTs
- Characterization of NTs
- NT – properties
-Lattice structure
- Multifunctional
composites

20
Models for Multiscale Effects
   Development of constitutive laws for nano-scale
- modeling of nano-structural behaviors
   Average nano-constitutive laws for use in higher scale
model
   Models for nano-structure/force potentials to take into
account of multi-scale model

Nanotechnology – Modeling Methods
• Quantum Mechanics
• Atomistic Simulations
• Molecular Mechanics and Dynamics
- nanomechanics                                    21
Nano-scale Measurement Techniques
and Tools
   Atomic Force Microscopy (AFM)
   Magnetic Force Microsopy (MFM)
- Scanning Electron Microscopy (SEM)
- Transmission Electron Microscopy (TEM)
- Scanning Tunnel Microscopy (STM)
Raman (IR) Spectroscopy
Electron Nano-Diffraction
Neutron Scattering
Electron Spin Resonance (ESR)

22
Nano-Structured Material Properties

Physical     Material            Mechanical
Thermal      Density             Stiffness
Optical      Crystallinity       Strength
Magnetic     Orientation         Fatigue
Chemical     Textures            Durability
Acoustic     Absorption           Viscoelastic

23
Mechanics of Carbon Nanotubes
   The structure of single wall nanotubes (SWNTs)
- molecules or crystals
- Effective geometry
- length scales
- geometric parameters
   Properties of Carbon nanotubes
- Thermal and electrical conductivities
- density
- mechanical properties such as modulus, strength
- effect of geometry and molecular structure
- classes of NTs
   Deformation of NTs
- Tension, compression, torsion
- nonlinear elastic and plastic deformation
24
Nanotubes Mechanical Properties

NASA Langley ResearchCenter [ ]   25
Nanotubes Density and Thermal Conductivity

26
VI: Nano-Scale Heat Transfer
   Classical theories breaks down
   Thermal energy transport in a solid by two
primary mechanisms:
- Excitation of the free electrons
- Lattice vibration or phonons
   Scattering phenomena dominates in micro and
nanoscale heat transfer

27
Basics of Heat Transfer
Heat transfer is thermal energy in   Basic Modes and
transit as a result of a spatial     Transport Rate Equation
temperature difference.
Conduction Heat
Temperature at a point is defined
by the energy associated with
Transfer
random molecular motions such as     This mode is primarily
translational, rotational and        important for heat transfer in
vibrational motions.                 solid and stationary fluid

Conduction heat transfer is
due to the activity in atomic
TH                           and molecular level
q
TL

28
Physical Mechanism                      Conduction Rate
Equation:
Gas: Energy transfer due to random
molecular motion and collision with
each other                                Fourier’s law:
Liquid: Molecular interactions are
more stronger and more frequent                         dT
resulting in an enhanced energy                q   kA
dx
transfer than in a gas
Solid: Energy transfer due to the         Where q = Heat flow per
Lattice vibration and waves induced
by the atoms.
unit area per unit time or
- In a electrical nonconductor, the     heat flux,
energy transfer is entirely due to    k is the thermal conductivity
lattice vibration waves.
- In a electrical conductor it also     of the material defined as
due to the translational motion of
the free electrons.
dT
k  (q / A) /
dx

29
Macroscopic Thermal Conductivity Values
of
Substance Type Density Thermal Conductivity
W
Gases:                          mo C

Air:                          0.026
Liquid
Water                         0.63
Ethylene Glycol                 0.25
Solid
Aluminum            2702       237
Copper              8930       401
Gold               19300       317
Carbon Steel        7850       60.5
SS 304              7900       14.9
Carbon
Amorphous       1950          1.6
Diamond         3500         2300
Silicon Carbide   3160          490         30
Convection Heat Transfer
The convection heat transfer occurs between a moving fluid and an
exposed solid surface.

u                                             Convection Modes:
y
Natural Convection:
T
Flow induced by natural
x
Hydrodynamic     TS   Thermal    forces such as buoyancy
Boundary layer        Boundary
layer
Forced: Flow induced by
The fluid upstream                              mechanical means such as
temperature and velocity                        fan, blower or pump.
are T and u
respectively.                                   Phase Change: Boiling
or condensation- Bubble
formations and collapses
31
Convection Rate Equation:
Newton’s Law Cooling
qc  hc A(TS  T )      Where, hc is called the convection
heat transfer coefficient or film
coefficient.
Convection heat transfer             qc / A              T
hc                kf A
coefficients is defined as         (TS  T )            y y  0

• Convection heat transfer coefficients are influenced by the
velocity field and temperature field in the boundary layers.
• This depends on fluid types and properties, solid surface
geometry and orientations.

32
Typical Convection Heat Transfer
Coefficients
W
Convection Types            Typical Values (   m2 o C
)
Free Convection
Gases                       2-30
Liquids                    50-1000
Forced Convection
Gases                     30 – 300
Liquids                   100 – 15000
Phase Change
Boiling or Condensation   2500 – 100,000

33
Nano-scale Heat Transfer
• Heat conduction in the micro-nanometer scale is
important because of the increasing demand of cooling in
smaller devices with increasingly higher heat fluxes such
as in electronic devices, circuits and chips

• The main difficulty  is that bulk material properties are
not accurate when applied on the small scale

• Mechanism of thermal energy transfer by     conduction in
nano-thin films is dominated by electron-phonon
scattering process.
.
34
Thermal Interactions

phonon – phonon interaction
electron – electron interaction
phonon – electron interaction
   In most pure metals, the electron – electron
interaction is the dominant scattering process
and the conduction of heat by phonon is
negligible
   In dielectric crystalline solid, the phonon –
phonon interaction is the dominant scattering
process and heat conduction by free electron is
negligible.                                       35
Applications nanothin films and
nanoparticles in Heat Transfer
   Used for enhanced conduction heat spreaders in
electronic chips, devices and circuits. Use of
dielectric thin films of diamond or nitrides

   Used as filler materials (SWNTs) between two
material surfaces in contact
-Reduces resistance to heat transfer

36
Nanofluids
Nanofluids are engineered colloid formed with stable suspensions
of solid nano-particles in traditional base liquids.
- Thermal conductivity of solids are order of magnitude higher
than liquids.
- Use of macro or micro-size particle can not form stable
suspensions
Base fluids: Water, organic fluids, Glycol, oil, lubricants and other
fluids             Al 2O3 ZrO 2 SiO 2 Fe3O4
Nanoparticle materials:
- Metal Oxides:
- Stable metals: Au, cu
- Nitrides: AIN, SIN
- Carbon: carbon nanotubes (SWNTs, MWNTs),
diamond, graphite, fullerene, Amorphous Carbon
- Polymers : Teflon                                            37
Major Characteristics and Challenges
 Stability in dispersion of nanoparticles in base fluid
- Nanoparticles can stay suspended for a longer period of
time
- sustained suspension is achieved by using
surfactants/stabilizers
 Surface area per unit volume is much higher for
nanoparticles
 Forming a homogeneous mixture of nanoparticles in
base fluid
 Reduce agglomeration of nanoparticles and formation of
bigger particles.
 Sedimentation over a period of time.
38
Nanofluid Heat Transfer
Enhancement
   Thermal conductivity enhancement
- Reported breakthrough in substantially increase (20-
30%) in thermal conductivity of fluid by adding very
small amounts (3-4%) of suspended metallic or
metallic oxides or nanotubes.

   Convective heat transfer enhancement

   Critical Heat Flux enhancement (CHF)
39
Enhanced Nanofluid Conductivity

Shows increase in effective thermal
conductivity of nanofluid with an
increase in temperature and CNT
concentration.
40
Possible Mechanisms for Enhanced
Thermal Conductivity
   Energy transport due to mixing effect of Brownian
motion of nanoparticles
   Formation of liquid molecule layerr around
nanoaprticles, enhancing local ordering (Phonon energy
transport)
   Balastic transport in nanoparticles – Balastic
phonon initated by a nanoparticle transmits through
fluid to other nanoparticles
   Possibility of formations of clusters of nanoparticles
   Micro convection and turbulence formed due to
nanoparticle concentration and motion.

41
Forced Heat Convection

42
Boiling Heat transfer
 Boiling is considered as convection which occurs at
solid-liquid interface.
 In the case of boiling fluid phase changes from liquid to
vapor through rapid formation of bubbles and
subsequent collapse in the bulk fluid.
- This causes heat transfer from solid heating surface
- Fluid temperature remains constant
– Latent heat contributes to the heat transfer
 Surface roughness influences critical heat flux.
- Critical heat flux can be enhanced by roughening
surface.

43
Critical Heat Flux Enhancement (CHF)
   Pool boiling heat transfer tests with nanfluids containing
alumina, zirconia and silica nanoparticles show increased
critical heat flux values (Kim et al. [2006]

   Nanoparticles settles and forms porous layer of heat surface
- Surface wettability increases
- Show increased contact angle on nanofluid boiled surface
compared to pure water boiled surface.

 Helps formation of bubbles at boiling surfaces
 Boiling heat transfer is increased mainly due to the formation
of nanoparticle coating on heating surface.

44
Enhanced Critical Heat Flux
Experiment with
nanofluid (suspending
alumina nanoparticles in
distilled water) indicate
increase in critical heat
flux by 200% in
comparison to pure
water.
The nucleate boiling
heat transfer coefficients
remain almost the same.
Kim and You [ ]
45
Nanofluid Applications
 Energy conversion and energy storage system
 Electronics cooling techniques
 Thermal management of fuel cell energy systems
   Nuclear reactor coolants
   Combustion engine coolants
   Super conducting magnets
   Biological systems and biomedicine

46
Nanofluids as Engine Coolant

Air                                                 Fuel
Diesel
Engine                                                Diesel
Air                                Engine
Fuel
Air Pre-heater

Engine
water
Nano-fluid
Cooling
loop
system                                   Heat
Exchanger
Engine water
Cooling loop
to Atmosphere

• Select potential nanofluids as coolant
• Develop correlations for heat transfer coefficients and
pressure drop for nanofluids
• Development of radiator, heat exchanger and air-
preheater using nanofluids.                                                              47
Group Project

Engine cylinders are typically cooled by forced convection heat transfer
technique by circulating water-glycol solution through the cooling jackets
around the cylinder walls.
• Identify new cooling techniques based on nanotechnology for improved
cooling system performance.
• Identify major advantages and gains
• Identify major challenges and technical difficulties
48
HOME WORK
Problem # 1
A load of 4000 N is suspended from three identically sized wire 1-
mm diameter. Wires are made of SS-304, Aluminum and wire
made of SWNTs. Determine the strain (deformation) produce in
three wires.

   Problem #2
http://www.ceet.niu.edu/cecourse/UEET101_Fall10/
Nanotech in ME homework.doc

49
Nanotechnology – Video clips

&feature=related
mg&feature=channel

50

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