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 ).
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Introduction To Convection

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Convection

Convection is defined as, "conduction + bulk fluid motion".
    • Velocity boundary layer  ↠  due to viscosity effects 
    • Thermal Boundary Layer  ↠  due to temperature gradient due to thermal exchange among the adjacent layers.

Boundary Layer Equation

We will be identifying the energy terms of a control volume which lies within the thermal boundary layer. Some used assumptions are:
    • Incompressible Flow
    • Steady State conditions
    • Constant thermophysical properties of fluid
    • Velocity boundary layer > Thermal boundary layer

Local and Average Convective Coefficient 

  • Convective coefficient vary from point to point.

Dimensionless Parameters

1. Reynold's Number 

It is the ratio of inertial forces to viscous forces. It tells about the type of flow (turbulent or laminar).

2. Prandtl Number 

It is a fluid property which tells the relation between velocity and thermal boundary layer.
    • For gases  ↠  δ  =  δt
    • For liquid metal  ↠  δt  >>  δ
    • For oil  ↠  δt  <<  δ

3. Nusselt Number 

Dimensional less heat transfer coefficient defining relationship between convective and pure conductive heat transfer.
Ques: Which convective coefficient used for what conditions?
    • For Laminar Flow 
      • At trailing edge over a full surface  ↠  Avg. Convective Coefficient 
      • At any point  ↠  Local Convective Coefficient 
    • For Turbulent Flow 
      • Avg. Convective Coefficient  ↠  Always
Note:

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).

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