Docstoc

Biofuels

Document Sample
Biofuels Powered By Docstoc
					UEET 101 Introduction to Engineering

        Nanotechnology
               in
     Mechanical Engineering
                  Presented By
                Pradip Majumdar
                     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
  loading
  - 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
                              Adhesion
                                            Structure property
 Scale:  106 m              Phases        relation
                                            Adhesion & friction laws15
      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: ??
                                     Energies are linked




                                                                 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
                             -Strain gradient
 - 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
Electronic   Crosslink density    Fracture toughness
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
   Heat Rejection   Radiator
                                                                            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
http://www.youtube.com/watch?v=sITy14zCvI8

http://www.youtube.com/watch?v=YcqvJI8J6Lc
  &feature=related
http://www.youtube.com/watch?v=zAIUsssNK
  mg&feature=channel



                                             50

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:1
posted:2/25/2013
language:English
pages:50