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Heat and Mass Transfer

, Volume 52, Issue 3, pp 621–634 | Cite as

Effect of jet-to-mainstream momentum flux ratio on mixing process

  • Alka Gupta
  • Mohamed Saeed Ibrahim
  • R. S. AmanoEmail author
Original

Abstract

Temperature uniformity after a mixing process plays a very important role in many applications. Non-uniform temperature at the entrance of the turbine in gas turbine systems has an adverse effect on the life of the blades. These temperature non-uniformities cause thermal stresses in the blades leading to higher maintenance costs. This paper presents experimental and numerical results for mixing process in coaxial ducts. The effect of increased jet-to-mainstream momentum flux ratio on the temperature uniformity of the exit flow was analyzed. It was found that better mixing of primary (or hot) stream and dilution (or cold) stream was achieved at higher flux ratio. Almost 85 % of the equilibrium mixture fraction was achieved at flux ratio of 0.85 after which no significant improvement was achieved while the exergy destruction kept on increasing. A new parameter, ‘Cooling Rate Number’, was defined to identify the potential sites for presence of cold zones within the mixing section. Parametric study reveals that the cooling rate numbers were higher near the dilution holes which may result in rapid cooling of the gases.

Keywords

Mixture Fraction Flux Ratio Exergy Destruction Momentum Flux Ratio Dilution Zone 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of symbols

Aclad

Area of cross-section of cladding

Aexit

Area of cross-section of exit section

Aholes

Total area of cross-section of the dilution holes

Aouter

Area of cross-section of outer duct

ed

Specific exergy destruction

f

Mixture fraction

fave

Weighted average mixture fraction

fequil

Equilibrium mixture fraction

h

Specific enthalpy

I

Jet-to-mainstream momentum flux ratio

\( \dot{m} \)

Mass flow rate

s

Specific entropy

T

Temperature

Tadb

Adiabatic, ideal mixing temperature

Ti

Local temperature

Tj

Dilution jet temperature

T

Main (or primary) stream temperature, before mixing

u*

Friction velocity at the nearest wall

ν, V

Velocity

Vave exit

Average exit flow velocity

Vave prim

Average primary inlet flow velocity

y

Distance to the nearest wall

Greek

ϑ

Kinematic fluid viscosity

ρ

Density of fluid

τw

Wall shear stress

Subscript

jet

Dilution jet

m

Mixed stream at the exit

o

Atmospheric

p, prim

Primary air

s, sec

Secondary air

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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • Alka Gupta
    • 1
  • Mohamed Saeed Ibrahim
    • 1
  • R. S. Amano
    • 1
    Email author
  1. 1.Department of Mechanical EngineeringUniversity of Wisconsin-MilwaukeeMilwaukeeUSA

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