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 ).

Steam Nozzles

Steam Nozzle

It is defined as, "a passage through which heat energy of steam is converted to kinetic energy by producing a high velocity jet of steam which is used to drive a steam turbine".
  • Nozzle  ↣  Increase velocity at the expense of pressure drop.
  • Throat  ↣  Produce steam jet with high velocity to drive steam turbine.
Types of Nozzles:
  1. Convergent Nozzle  ↣  Cross-section decreases continuously from entrance to exit.
  2. Divergent Nozzle  ↣  Cross-section increases continuously from entrance to exit.
  3. Convergent-Divergent Nozzle  ↣  Cross-section first decreases from entrance to throat, then increase from its throat to exit.

Stagnation State

For a high speed flows (in jet engines), P.e. is negligible but K.e. is not. It is convenient t combine enthalpy and K.e. of the fluid into a single term called Stagnation or Total Enthalpy.
ho = h + 0.5 V^2
  • Total or Stagnation State  ↣  state in which flow is brought to rest isentropically in steady flow, zero adiabatic work output.
  • Dynamic Temperature  ↣ temperature change when molecules are moving.

Velocity of Sound & Mach Number

Sound wave is defined as, "a small pressure disturbance that propagates through a states (gas, liquid, solid)".
  • Velocity of wave depends on properties of the medium.
Mach Number  ↣ the ratio of actual velocity and the velocity of sound.
  • If M < 1  ↣ Subsonic Flow.
  • If M = 1  ↣ Sonic Flow.
  • If M > 1  ↣ Supersonic Flow.

Variation of Fluid Velocity with Flow Area

The last equation concludes that:

Stagnation Property Relations (Critical Pressure Ratio & Choked Flow)

Effect of Back Pressure in Convergent Nozzle

Back Pressure is defined as, "the pressure applied at the nozzle discharge region".
  • Condition of Flow ↣ pressure difference between inlet and outlet.
  • Choked Flow ↣ when nozzle operates with maximum mass flow (done by reducing back Pressure to critical pressure). 
  • Critical Pressure  ↣  pressure of fluid at a location in the nozzle where M=1 (at throat).

Note:

References:

  • Material from Class Lectures + Book named Power plant Engineering by P.K Nag (4th Edition) + My knowledge. 
  • Photoshoped pics are developed. 
  • Some pics and GIF from Google.  
  • Videos from YouTube (Engineering Sights).

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