Nanotechnology in Mechanical Engineering

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Nanotechnology in Mechanical Engineering
UEET 101 Introduction to Engineering

• Presented By
• Pradip Majumdar
• 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
• Material mechanical properties
• 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 nanomechanics
• 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 -give 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 of 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

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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
  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

Defined based on balance of external force with
the internal resistance force as
Where Average stress (Internal
resistance force per unit area) F External
load or force A Cross-sectional area over
which the force acts
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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
• Where E Modulus of Elasticity (Youngs
  Modulus)

• Elastic modulus (E) is a measure of the stiffness
  of the engineering material
• Greater the values of E results in a smaller
  elastic strains smaller the response of the
  material structure to imposed load
• Important parameter for the 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 G is usually determined by torsion
• testing and related to 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 uniaxial loading
• - undergone 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
• 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
  Tension Posssonsratio
• 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

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Breakdown of Continuum Concepts- Thresholds of
Micromechanics

• Macromechanics

Force, stress balance/equilibrium Constitutive
relation Hooks law 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
Micromechanics

• 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 of 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 molecuar 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 polymer properties
• Multifunctional composites

• Approaches- Top down
• Continuum models fro NTs
• Strain gradient
• Lattice structure

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Models for Multiscale Effects

• Development of constitutive laws fro nano-scale
• - modeling of nano-structural behaviors
• Average nano-constitutive laws for use 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-Difraction
• 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
NASA Langley ResearchCenter
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Nanotubes Density and Thermal Conductivity
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VI Nano-Scale Heat Transfer

• Classical theories
• Thermal energy transport in a solid by two
  primary mechanisms
• - Excitation of the free electrons
• - Lattice vibration or phonons
• Scattering phenomena 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 waves.
• - In a electrical conductor it also 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 the micro-nanometer scale is
  becoming more important because of the increasing
  demand of cooling requirements in smaller devices
  with increasingly higher heat fluxes such as in
  electronic devices, circuits and chips
• The main difficulty with the simulation of heat
  flow through thin films is that bulk material
  properties are not accurate when applied on the
  small scale
• The understanding of the mechanism of thermal
  energy transfer by conduction in thin films
  ranging in thicknesses from micro-scale to
  nano-scale is becoming very important.
• Thin films should be modeled at the atomic level
  and this entails treating the heat transfer as
  energy transferred by the vibrations in a crystal
  lattice.

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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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Heat Conduction Dielectric Thin Films

• The vibration of a crystal structure can be
  modeled with the concept of phonons, which is
  described as the quanta of lattice vibration
  energy.
• The distribution of phonons represents the
  distribution of crystal energy. Heat
  transmission takes place as the distribution of
  phonons changes.
• When a temperature gradient is setup in the
  material a steady
• state distribution of phonons can be kept.
• Thermal conductivity therefore depends on the
  extent by which a distribution deviates from
  equilibrium for a given temperature gradient.
• The distribution of phonons is modeled by the
  Boltzmann transport equation

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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

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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 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
• 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 articles.
• 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 metallic 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 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.

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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
• 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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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
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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 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.

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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

• Selection potential nanofluids as coolant
• Develop correlations for heat transfer
  coefficients and
• pressure drop
• 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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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
• A square chip of width 5-mm in size is
  mounted on a substrate that is insulated in all
  sides while the top surface is cooled to
  dissipate heat generated in the chip. From
  reliability point, the chip surface has to be
  maintained at 85 C. Determine the maximum
  allowable chip power for he following three
  cases
• a) Forced convection with water at 20 C
  and h 2000
• b) Forced convection with nanofluid made
  of water and copper
• naoparticles at 20 C and h 2500

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• http//www.youtube.com/watch?vsITy14zCvI8