Radiation Heat Transfer

-
Image
View Factor Orientation (or View factor or shape factor) plays an important role in radiation heat transfer. View factor is defined as, "fraction of radiation leaving surface 'i' and strike 'j' ". Summation Rule (View Factor) If there is are similar surfaces 'i' and 'j' , then: Blackbody Radiation Exchange Radiation Exchange between Opaque, Diffuse, Gray surfaces in an Enclosure 1. Opaque 2. Surfaces 3. Two surface enclosure Radiation Shield It is used to protect surfaces from radiation act like a reflective surface. References: Material from Class Lectures + Book named Fundamentals of Heat and Mass Transfer by Theodore L. Bergman + My knowledge.  Photoshoped pics  are developed.  Some pics and GIF from Google.   Videos from YouTube ( Engineering Sights ).
Post a Comment

Nano-Materials

-

Nano-Materials 

It is defined as, "materials having size of individual building blocks less than 100 nm".
  • Bulk gold  ↔  have no catalytic properties but Au-Nanocrystal  ↔  excellent low temperature catalyst.
Why Nano-materials?
At nanoscale strange things happen to materials and their properties may change.
  1. Reactivity  ↔  smaller particles react differently with their environment than larger particles.
  2. Size  ↔  have different optical and reflection properties.
  3. Magnetism  ↔  have different magnetic properties.

Nanomaterials Synthesis Technique

It includes design and preparation of nanomaterials with high functionality (i.e. to fabricate nanoparticles with suitable properties).
Synthesis involves the control of size, shape, structure and composition and purity of constituents.
  1. Method of synthesis
  2. Growth Kinetics

1. Method of Synthesis

Two approaches are used:

a. Top-Down Approach

  • Refers to slicing or cutting of bulk materials.
  • Biggest problem is imperfection of structure surface.
  • It involves cutting, grinding, ball milling of solid state.

b. Bottom-Up Approach

  • Refers to build-up of material from bottom, atom-by-atom, molecule-by-molecule or cluster-by-cluster.
  • Better chance to obtain nanostructures with less defects, more homogenous chemical composition.
  • Physical Vapor Disposition Technique (PVD) ↔ involves evaporation, sputtering, plasma arcing, laser ablation.

2. Growth Kinetics

Synthesis of nanoparticles is a combination of two stages: Nucleation and Growth.
  • Nucleation  ↔  in which nuclei (seeds) act as templates for crystal growth.

Properties of Nano-Particles

  1. Catalytic  ↔  Better catalytic efficiency through higher surface to volume ratio.
  2. Electrical  ↔  Increase electrical conductivity in Ceramics. Increase electrical resistance in Metals.
  3. Magnetic  ↔  Increase magnetic coercivity up to a critical grain size, super paramagnetism.
  4. Mechanical  ↔  Improve hardness and toughness in metals and alloys and ductility and super-plasticity in Ceramics.
Note: 

References:

  • Material from Class Lectures + Book named Materials Science and Engineering: An Introduction by Callister and Rethwick + my knowledge. 
  • Pics and GIF from Google Images.  
  • Videos from YouTube (Engineering Sights).

Comments

Post a Comment

HI, we wI'll contact you later

Popular posts from this blog

Orthographic Projections

-
Image
Projection: The term Projection is defined as: Presentation of an image or an object on a surface. The principles used to graphically represent 3-D objects and structures on 2-D media and it based on two variables: Line of Sight.  Plane of Projection.  Line of Sight & Plane of Projection: Line of sight is divided into 2 types: Parallel Projection Converging Projection  & A plane of projection is an imaginary flat plane upon which the image created by the lines of sight is projected. Orthographic Projection: When the projectors are parallel to each other and perpendicular to the plane of projection. The lines pf sight of the observer create a view on the screen. The screen is referred to as the Plane of Projection (POP). The lines of sight are called Projection lines or projectors. Rules of Orthographic Projection: Edges that are parallel to a plane of projection appear as lines. Edges that are incl...
Read more

Flywheel

-
Image
Flywheel It is defined as, " a machine element which serves as reservoir which stores energy during the period when energy supply is more than the requirement and releases it when energy is less than requirement " . Used in IC, reciprocating (compressors or pumps) engines, presses, etc. Excess energy is stored in flywheel and release to crankshaft during other strokes in which no energy is developed. If space is small   ↠ use small diameter and solid flywheel . If space is not limited (like for presses, crushing machine, hammering machine)  ↠  use large diameter and hollow flywheel . Purpose of flywheel is to: reduce amplitude of speed fluctuation (sinusoidal) for constant power output. reduce maximum torque required. energy stored and release when needed during cycle. Parts of flywheel are Rim   ↠  outer portion of flywheel (which is like a wheel). Hub   ↠  center part which is installed on shaft. Arms or Needle   ↠  rods joining rim to ...
Read more

Angles & Directions

-
Image
Angles & Directions Angles are also called bearings. Bearings are the acute angles between lines and meridians. They are divided into following types. Related Terms : Meridian : Imaginary line joining North and South poles. Declination : Difference between magnetic and true meridians. Azimuth : Clockwise angle taken from Geodatic North. * If area is greater ➤ use Geodatic North * If area is smaller ➤ use Magnetic North Magnetic Declination maybe towards East or West. For east     ➤       Magnetic bearing=true bearing - Declination For west    ➤       Magnetic bearing=true bearing + Declination Forward Bearing : Bearing taken in the direction of traverse. Backward Bearing : Bearing taken in opposite direction of traverse. Forward bearing - Backward bearing=180 For anti-clockwise :  FB of line = BB of previous line + angle Example: In an anti-clockwise traverse <A=102'30',...
Read more