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

Fluid Kinematics

-

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).

Comments

Post a Comment

HI, we wI'll contact you later

Popular posts from this blog

Corrections Of Tape

-
Image
TAPING CORRECTIONS There are two types of corrections depending upon the type of errors in tape due to the different conditions.  1. Systematic Errors : Slope Erroneous tape length Temperature Tension Sag 2. Random Errors : Slope  Alignment Marking & Plumbing Temperature Tension & Sag 1. Temperature Correction  It is necessary to apply this correction, since the length of a tape is increased as its temperature is raised, and consequently, the measured distance is too small.  It is given by the formula,                         C t  = 𝛼 (T m  – T o )L Where,   C t  = the correction for temperature, in m.      𝛼 = the coefficient of thermal expansion.    T m  = the mean temperature during measurement.          T o  = the tempe...
Read more

Diffusion

-
Image
Diffusion  It is defined as, " The transportation of one atom from one state into other state " . Used for hardening of surfaces like die parts, gear, bolt, machine element. Hardening can be done using Temperature-Heat treatment ( diffusion couple ). There are two types of diffusion: Inter-diffusion   ↔ in which atoms tend to migrate from region of high concentration to low concentration . Self-diffusion   ↔  in which atoms migrate within a solid. Diffusion Mechanism There can be two conditions of moving atoms Empty spaces between adjacent sites. Atoms have sufficient energy to break bond with neighbors atoms which cause lattice distortion during displacement. If we rise temperature, small fractions of atoms is capable of diffusive motion (which cause lattice distortion). Types of Diffusion 1. Vacancy Diffusion It is defined as, " interchange of an atom from a normal lattice position to the adjacent vacant lattice site " . Extent of vacancy diffusion is a function...
Read more

Gear Forming by Machining

-
Image
Gear Forming by Machining Formation of gear through machining consists of following methods: Form Milling by Disc Cutter Form Milling by End Mill Cutter Shaper, Planner and Slotter Broaching 1. Form Milling by Disc Cutter It is defined as, " Tooth is cut one by one by plunging the rotating cutter into the blank " .  Each gear needs a separate cutter. 8 - 10 standard cutters are available for producing 12 - 120 teeth gears. Used for big spur gears of large pitch. 2. Form Milling by End Mill Cutter It includes the cutting of tooth at a time and then indexed for the next tooth space for cutting. For a small volume production of low precision gears. Set of 10 cutters   ↠  12 - 120 teeth gears . Used for teeth of large gears/module. To reduce cost, same cutter is often used for multiple sized gears resulting in profile errors . Characteristics: Use of Hardened stainless steels (HSS) form milling cutters. Use of Ordinary milling machines. Low production rate (need of indexing...
Read more