Nanotechnology in Mechanical Engineering

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Nanotechnology in Mechanical Engineering
UEET 101 Introduction to Engineering

• Presented By
• Pradip Majumdar, Ph.D
• Professor
• Department of Mechanical Engineering
• Northern Illinois University
• DeKalb, IL 60115

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Outline of the Presentation

• Lecture
• In-class group activities
• Homework

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Lecture II Outline

• Nano-Mechanics
• Classical Mechanics Assumptions
• Mechanical Properties of Materials
• Nanoscale Thermal Phenomena
• - Basics of Heat Transfer
• - Thermal Conductivity
• - Heat Transfer Coefficients

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Nanomechanics

• Classical theories
• Structure Property relations
• Stress-strain relations
• Mechanical properties
• Issues in Nano-mechanics
• Mechanics of Nanotubes

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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 EnergyKinetic Energy
  
• Potential Energy
• Single phase
• no phase transformation

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Basics of Classical Mechanics

• Mechanical Behavior of Materials
• Materials 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 repulsive forces into play.

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• 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
defined as the ratio of the dimensional change to
the original dimension.
Extensional Strain
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• 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 ratio
  of displacement to the distance between the
  planes

Poissons Ratio Defined as the ratio of strain in
x-direction to the strain in y-direction and
expressed as
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• 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

Where Average stress (Internal
resistance force per unit area) F External
load or force A Cross-sectional area over
which the force acts
Defined based on the balance of external force
with the internal resistance force as
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• Hookss Law (Macroscopic Constitutive
• Relation or Stress-strain
  relation)
• Defines the proportional relation between the
• stress and strain for material below the
  elastic
• limit as Linear
  relation
• Where E Modulus of Elasticity (Youngs
  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

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• 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
• Values of modulus of rigidity (G) is usually
• determined by torsion testing and related to
• modulus of elasticity (E) by the relation

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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
• uni-axial loading
• - undergoes substantial plastic deformation
• - not often used for designing a component

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Beam Deformation for Different Materials

• Many materials are not strength limited, but
  modulus limited (E)
• In some applications, we need material of high
  modulus of elasticity rather than high strength
• These structure may not fail if low modulus of
  elasticity is used
• It, however, may reach too much of deflection

Higher the modulus of elasticity lower is the
deformation
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Typical Material Properties

• Material Elastic Shear
  Tensile Poissons ratio
• 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
• Silicon Carbide 469.2
• Polycarbonate 3.4
• SWNT 0.191(TPa) 0.45 (TPa)
  0.18

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Breakdown of Continuum Concepts- Thresholds of
Micromechanics

• Macromechanics

Force, stress balance/equilibrium Constitutive
relation Hooks law linear Classical
thermodynamics
Stress Strain Area/volume
Scale
Micromechanics
Force/surface energy balance Constitutive
relation nonlinear Structure property
relation Adhesion friction laws
Structure Interface Adhesion Phases
Scale
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Breakdown of Continuum Concepts- Thresholds of
Nanomechanics

• Nanomechanics

Force/energy/structure balance Constitutive
relation ?? Molecular mechanics
effects Structure property relation ?? Energies
are linked
Molecule Atoms Quantum energies
Scale
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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

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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

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Nanomechanics

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

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Issues in Nanomechanics

• Nano-Materials Science
• - Nanotubes purity
• - Characterization of NTs
• - NT properties
• Multifunctional composites

• Approaches- top down
• Continuum models for NTs
• Strain gradient
• Lattice structure

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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

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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)

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Nano-Structured Material Properties

• Physical Material
  Mechanical
• Thermal Density
  Stiffness
• Optical Crystallinity
  Strength
• Electronic Crosslink density
  Fracture toughness
• Magnetic Orientation
  Fatigue
• Chemical Textures
  Durability
• Acoustic Absorption
  Viscoelastic

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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

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Nanotubes Mechanical Properties
Source NASA Langley Research Center
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Nanotubes Density and Thermal Conductivity
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VI Nano-Scale Heat Transfer

• Classical theories breaks down
• Thermal energy transport in a solid by two
  primary mechanisms
• - Excitation and motion of the free
  electrons
• - Lattice vibration or motion phonons
• Scattering phenomena dominates in micro and
  nanoscale heat transfer

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Basics of Heat Transfer
Basic Modes and Transport Rate Equation Conductio
n Heat Transfer This mode is primarily important
for heat transfer in solid and stationary
fluid Conduction heat transfer is due to the
activity in atomic and molecular level

• Heat transfer is thermal energy
• In transit as a result of a spatial
• temperature difference.
• Temperature at a point is
• defined by the energy
• associated with random
• molecular motions such as
• translational, rotational and
• vibrational motions.

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Physical Mechanism
Conduction Rate Equation

• Gas Energy transfer due to
• random molecular motion
• and collision with each other
• Liquid Molecular interactions
• are more stronger and more
• frequent resulting in an
• enhanced energy transfer
• than in a gas
• Solid Energy transfer due to
• the Lattice vibration and
• waves induced by the atoms.
• - In a electrical nonconductor, the energy
  transfer is entirely due to lattice vibration
  waves.
• - In a electrical conductor it is due to the
  translational motion of the free electrons.

Fouriers law
Where q Heat flow per unit area per unit time
or heat flux, k is the thermal conductivity of
the material defined as
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Macroscopic Thermal Conductivity Values of
Substance Type Density Thermal
Conductivity Gases 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
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• Convection Heat Transfer
• The convection heat transfer occurs between a
  moving
• fluid and an exposed solid surface.
• The fluid upstream
• temperature and velocity
• are and
• respectively.

Convection Modes Natural Convection Flow
induced by natural forces such as
buoyancy Forced Flow induced by mechanical means
such as fan, blower or pump. Phase Change
Boiling or condensation- Bubble formations and
collapses
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• Convection Rate Equation
• Newtons Law Cooling

Where, is called the convection heat
transfer coefficient or film coefficient.
Convection heat transfer coefficients is defined
as

• 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.

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Typical Convection Heat Transfer Coefficients

• Convection Types Typical Values
  ( )
• Free Convection
• Gases
  2-30
• Liquids
  50-1000
• Forced Convection
• Gases 30
  300
• Liquids 100
  15000
• Phase Change
• Boiling or Condensation 2500 100,000

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Nano-scale Heat Transfer

• Heat conduction in micro-nano 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 use of bulk
  material properties is not accurate when applied
  on the nano scale
• Mechanism of thermal energy transfer by
  conduction in nano-thin films is dominated by
  electron-phonon scattering process.
• .

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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.

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Applications of 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

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Nanofluids

• Nanofluids are engineered colloid formed with
  stable suspensions of solid nano-particles in
  traditional base liquids.
• - Thermal conductivity of solids is an 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
• Nanoparticle materials
• - Metal Oxides
• - Stable metals Au, cu
• - Nitrides AIN, SIN
• - Carbon carbon nanotubes (SWNTs,
  MWNTs),
• diamond, graphite, fullerene,
  Amorphous Carbon
• - Polymers Teflon
• Nanoparticle size 1-100 nm

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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.

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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 metals or metallic oxides or nanotubes.
  
• Convective heat transfer enhancement
• Critical Heat Flux enhancement (CHF)

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Enhanced Nanofluid Conductivity
Shows increase in effective thermal conductivity
of nanofluid with an increase in temperature and
CNT concentration.
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Possible Mechanisms for Enhanced Thermal
Conductivity

• Energy transport due to mixing effect of Brownian
  motion of nanoparticles
• Formation of liquid molecule layer around
  nanoaprticles - enhancing local ordering (Phonon
  energy transport)
• Balastic transport in nanoparticles Balastic
  phonon initiated by a nanoparticle and and
  transmits through fluid to other nanoparticles
• Possibility of formations of clusters of
  nanoparticles
• Micro convection and turbulence formed due to
  nanoparticle concentration and motion.

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Forced Heat Convection
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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.

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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 over
  heating 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.

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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.
Source Kim and You
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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

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Nanofluids as Engine Coolant

• 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.

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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

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Nanotechnology Video clips

• http//www.youtube.com/watch?vsITy14zCvI8
• http//www.youtube.com/watch?vYcqvJI8J6Lcfeature
  related
• http//www.youtube.com/watch?vzAIUsssNKmgfeature
  channel