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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Bathymetric operation in Hydrographic Survey

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Hydrographic Survey

Uses:

  • It is used to determine mean sea level and observation of tides in oceans, lakes, Bayer and harbors.
  • Used to find water depths and locations of rocks, sand bars for navigation channel opening and salvage operation.
  • Determination of pollution sources. 
  • For designing of projects like dams, bridges, reservoirs, port, harbors and many alot.
  • Preparation of nautical charts(nautical chart is the graphical representation of a sea area and the adjacent coastal regions. 
  • Through the knowledge of Hydrographic Survey we can prepare navigation charts.

Objectives of Hydrographic Survey

  1. Measurements of wavelengths of tides and waves.
  2. Construction of sea defence works. 
  3. Determination of bed depth.
  4. Location of underwater features. 
  5. Off shore engineering and shipping industries and many more things.

Bathymetric operations in Hydrographic Survey 

Hydrographic Echo Sounder:

Hydrographic Echo Sounder is used to find the depth of seafloor by using the properties of acoustic waves. It's basic principles is to measure the time which is required by wave when it is transmitted and reflected back like echo at seafloor.
Hydrographic Echo Sounder is further divided into 2 types :
1. Single Beam Echo Sounder 
2. Multi Beam Echo Sounder


1. Single Beam Echo Sounder(SBES) :

It is also called depth Sounder which determines the depth of water by time travel measurement of a short sonar pulse or ping.
The emitter or instrument is placed just below water surface and SBES listens for the return echo from the bottom. By this method we accurately determine the depth of water. SBES may use different frequencies, typically at 100m 200 kHz is used but if the frequency is decreased about 24-33kHz then it can be used for deeper water survey. Results from SBES are easier to interpret, less time consuming and this equipment may be operated by less experienced persons.

2. Multi Beam Echo Sounder (MBES) :

In MBES, the sounding system emits sound in the form of waves. The time taken by the sound waves to strike the sea beds and bounced back to the receiver, is used to determine the depth of water. Echo Sounder can also be used to map the sea floor or to look for the specific items such as underwater ancient things or shipwreks. MBES shows the higher density of data. 
Multi beam echo sounders is not ideal for work in shallow river areas but has been produced for ocean and coastal survey. It works wonderfully with the depth of more than 100ft.

The difference between the multibeam and single Beam Echo Sounders is totally illustrated in the given pictorial presentation. 

References:

  • Combined project on Hydrographic Survey by Taha Nasir, Rameez, Anas & Talha Shafique.

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