Radiation Heat Transfer

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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 ).

Crystal Structures

Crystalline Solids and it's Structures

Crystalline Solids are defined as, "atoms arranged in periodic manner over long atomic distances in 3D patterns".
  • It deals with the unit cell (smallest part of structure).
  • If no 3D pattern  ⇔  non-crystalline or amorphous solids.
  • Single Crystal  ⇔  all unit cells interlock in the same way in the same orientation.
  • Polycrystalline Material  ⇔  collection of small crystals (or grains) having random crystallographic orientation.
There are two types of unit cells, namely
  1. Hard-Sphere unit cell
  2. Reduced-Sphere unit cell

Types of Crystal Structures

Following are the types of crystal structures:

1. Face-Centered Cubic (FCC) Crystal Structure

It is defined as, "Unit cell of cubic geometry in which atoms are located at each of corners and centers of all cubic faces".
  • Each corner atom is shared among 8 unit cells.
  • Face-centered atom shared with 2 unit cells.

2. Body-Centered Cubic (BCC) Crystal Structure

It is defined as, "Cubic unit cell with atoms located at all eight corners and single atom at cubic center".
  • Center and corner atoms touch one another along cube diagonals.
  • Coordination number of BCC is 8.

3. Hexagonal Close-Packed (HCP) Crystal Structure

It is defined as, "Unit cell having cubic structure and have top and bottom faces consist of 6 atoms that forms regular hexagon and surround a single atom in the center".
  • Three additional atoms  ⇔  provided to a plane between top and bottom face.
  • Coordination number is 12.
  • Atomic Packing factor is 0.74.

Stacking Sequence

It is defined as, "conversion of 2D layers to 3D structures to minimize empty spaces".

Important Terms

  • Point Coordinates  ↔  are lattice parameters. It can be used to define which plane is more denser.
  • Crystallographic Directions  ↔  Line between two points.
  • Crystallographic Planes  ↔  Set of equally spaced planes that may be supposed to pass through the center of atoms in a crystal.
  • Linear Atomic Density  ↔  It is the ratio between number of atoms and unit length of direction vector.
  • Theoretical Density  ↔  Crystal structure of metallic solid permits computation of its theoretical density through the relationship.

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.

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