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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Fluid Kinematics

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Fluid Kinematics

It is defined as, "study of motion of a body without considering the forces acting on it".
  • If particle follow path  ⇰  Langrangian Approach (analogous to closed system analysis in thermodynamics).
  • For Flow field, Material derivative  ⇰  click here.
  • Unsteady Effects  ⇰  deals with properties (like velocity, temperature, density) changes with time.
  • Convective Effects  ⇰  change in acceleration due to change in space represented by spatial derivative.
  • For Flow Pattern and Visualization  ⇰ click here. 

Stream Tube

It consists of a bundle of individual streamlines (like cables) which tells us whether the flow is accelerating or decelerating.
  • If steady flow  ⇰  streamlines = pathlines = streaklines.

Potential Lines

These are the lines joining points of equal velocity potentials on streamlines.

Flow Net

A grid obtained by drawing a series of stream lines and equipotential lines.
  • Flow net analysis assist design of an efficient boundary shapes.
  • Used to calculate the flow at ground level.

Refractive Flow Visualization Technique

Flow visualization method used refractive property of light waves. There are two methods, namely:
  1. Shadowgraph Technique
  2. Schileren Technique

Plots of Flow Data

It is the representation of flow properties varying in time or space.
  1. Profile Plot  ⇰  line graph
  2. Vector Plot  ⇰  array of arrows indicating vector properties in time.
  3. Contour Plot  ⇰  curves of contact values.

Types of Fluid Flow

1. 1D, 2D and 3D Flow

  • 3D Flow  ⇰  Three velocity components are important and of equal magnitude. For eg: flow passes a wing.
  • 2D Flow  ⇰  One of the velocity components may be small relative to other two. For eg: flow over an airfoil.
  • 1D Flow  ⇰  Two velocity components may be small relative to other one. For eg: flow in open channel.

2. Steady & Unsteady Flow

  • Steady Flow  ⇰  flow is not changing with time.
  • Unsteady Flow  ⇰  flow is changing with time at a particular cross-section.

3. Uniform & Non-Uniform Flow

  • Uniform Flow  ⇰  flow in which velocity is not changing with respect to space.
  • Non-Uniform Flow  ⇰  flow in which velocity is changing with space.

4. Laminar & Turbulent Flow

  • Laminar Flow  ⇰  Smooth flow and Re < 2300.
  • Turbulent Flow  ⇰  Efficient mixing, velocity at any point fluctuates and Re > 4000.

5. Rotational & Irrotational Flow

  • Rotational Flow  ⇰  The flow in which fluid particles while flowing along streamlines rotate about their own axis.
  • Irrotational Flow  ⇰  Flow in which fluid particles do not rotate about their own axis.

6. Compressible & Incompressible Flow

  • Compressible Flow  ⇰  if density is changing with time (mostly gases).
  • Incompressible Flow  ⇰  if density is not changing with time (mostly liquids).

Control Volume and System Representation

System Approach (Integral approach)  ↠  no mass crosses the boundary and the total mass of the system remain fixed.
Control Volume Approach (Differential approach)  ↠  mass crosses the boundary (fixed interior volume).
  • Control Surfaces  ↠  Boundaries which allow flow in or out.
  • Reynolds Transport Theorem (RTT)  ↠  Relation between time rates of change of an extensive property for a system and for a control volume (i.e. relation between system and control volume approach).

Reynolds Transport Theorem (RTT)


The assumptions made during RTT Derivation are given below:
  1. Fixed control volume.
  2. One inlet and one outlet.
  3. Uniform Properties.
  4. Normal velocities to I and II sections.
If there were more than one inlet and one outlet:
  • Sum the Inlets  ↠  I = I1 + I2 + I3 + . . . + In.
  • Sum the Outlets  ↠  II = II1 + II2 + II3 + . . . + IIn.  
If velocity is not normal to the control surface:
The assumptions are: 
  1. Time rate of change of extensive parameter of a system mass, momentum, etc.
  2. Time rate of change of extensive parameter within CV.
  3. Net flow rate of extensive parameter across entire CS.

Relationship between Material Derivative & RTT

  • RTT deals with finite size CV (integral analysis).
  • Material derivative deals with infinitesimal fluid particles (differential analysis).
Note:

References:

  • Material from Class Lectures + Book named Fundamentals of Fluid Mechanics by Munson, Young & Okiishi's (8th Edition) + my knowledge. 
  • Pics and GIF from Google Images.  
  • Videos from YouTube (Engineering Sights).

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