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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Intrumentation

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SURVEYING INSTRUMENTS

We are discussing intruments like total station, theodolite, EDMI and military compass.

1. Total Station:

A total station is an electronic and optical instrument used in modern surveying and is designed for measuring slant distances, horizontal & vertical angles, elevation, i.e, it is the combination of EDMI and theodolite.

Parts of Total Station :

  • Alidade: used for rough alignment.
  • Focusing Knobs: used in focusing the target object 
  • Eye-piece: used to see the object.
  • Leveling Screws: used to level the instrument.
  • Display Panel: the screen where the data is shown.
  • Clamps: they are used to lock down the vertical and horizontal motion.
  • Optical Plummet: used for centering the instrument.

Working :

Set the total station on a station by leveling and centering. Switch on the machine and rotate the machine once in horizontal and once in vertical position to activate the machine. Then check the leveling on the screen by pressing FNC (to change page) and choose TILT option by pressing F4. Now change the reflector type on page 1, F3 and set reflectors. Now, you can find the distance, elevation, angles etc.

2. Theodolite :

A theodolite is an optical instrument used for measuring angles. Theodolite is further divided into 2 types:
  1. Transit theodolite
  2. Non-transit theodolite

Parts of Theodolite :

  • Eyepiece & objective lens
  • Tripod stand 
  • Horizontal clamp & tangent screw
  • Vertical clamp & tangent screw
  • Vertical plummet
  • Objective & Eyepiece focus
  • Leveling screws 
  • Vertical circle
  • Bubble tube 
  • Battery
  • Electronic display & operation keys for digital theodolite 
  • Manual scale for manual theodolite 

Working :

A theodolite may be in perfect adjustment and lines and planes should be checked. To minimize error, an angle is measured a number of times with instrument: face left & face right. Reading an angle face left and right will eliminate the errors due to the non-adjustment of line of collimation and trunnion axis. 
Temporary adjustments are a set of operation, necessary in order to make theodolite ready for taking observations. These include centering, leveling, setting up and elimination of parallax. 
A theodolite works by combining optical plummet, spirit level and graduated circles. 

3. Electronic Distance Measuring Instrument (EDMI) :

EDMI is a surveying instrument used for measuring distance electronically between two points through electromagnetic waves. 

Parts of EDMI :

  • Frequency generator 
  • Filter (variable & interference) 
  • Modulator
  • Retro reflector 
  • Amplifier 
  • Display screen
  • Phase meter 
  • Beam splitter
  • Transmitter & Receiver

Working :

EDMI are further categorized into long wavelength, microwave and visible instruments depending upon the distance to be measured. 

An EDMI does its operation in following steps:

Transmittance & Modulation :

The instrument uses a system of mirrors to produce a narrow collimated beam. The wavelength of carrier wave is relatively short, so it is modulated and is transmitted by a radiator. Then a beam splitter divides this beam into internal and external beam. 

Reflector :

The instrument uses retro-reflector to send back the transmitted signals to the master station. 

Reception & Display :

The internal beam passes through a variable density filter to make it identical to the reflected beam. Both of them after passing through interference filter produce any undesired energy. The resulting weak signals is them amplified and passes through pahse discriminator which converts them into electrical signal and the distance is displayed on the screen. That's how EDMI works.

4. Military Compass (Lensatic compass) :

Military compass is used to determine the bearing and azimuth. It is used for attaining direction. 

Parts of a Military Compass :

  • Luminous magnetic arrow
  • Short luminous line 
  • Fixed index line
  • Thumb loop
  • Sighting slot
  • Lense 
  • Floating dial 
  • Cover

Working :

The most precise method of using a compass is similar to a handgun. Unfold the compass so the cover is at 90 degree and the lens is at 30 degree. Place your thumb on the thumb loop and support it with the rest of your fingers. Bring the compass close to your eye, so the thumb loop is touching your cheek. Look through the lens and align the distant object with the sighting wire. Now you can find bearings or azimuths. 

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