Abstract
Turbulent heat transfer from a sudden expansion pipe subjected to an externally convective boundary condition is studied numerically using the proposed modified turbulence model. Both HYBRID and QUICK schemes are employed for comparison purposes. The calculated velocity distribution and turbulent kinetic energy show a significant improvement over the existing model solutions. The present results of center-line velocity, temperature distribution and Nusselt number under a limiting condition compare well with the available experimental data.
Zusammenfassung
Mittels des vorgeschlagenen modifizierten Turbulenzmodells wurde die turbulente Wärmeübertragung in der Nähe einer abrupten, extern einer konvektiven Grenzbedingung unterliegenden Rohrerweiterung untersucht. Sowohl HYBRID- als auch QUICK-Verfahren fanden zu Vergleichszwecken Anwendung. Die berechnete Geschwindigkeitsverteilung und die turbulente kinetische Energie zeigen eine signifikante Verbesserung gegenüber den existierenden Modell-Lösungen. Die vorliegenden Ergebnisse für die Geschwindigkeit entlang der Mittellinie, die Temperaturverteilung und die Nusselt-Kennzahl stimmen unter einschränkenden Bedingungen gut mit vorhandenen experimentellen Daten überein.
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Abbreviations
- A :
-
model constant
- C f :
-
friction coefficient
- C 1,C 2,C μ :
-
model constants
- C p :
-
specific heat
- d :
-
diameter of inlet pipe
- D :
-
diameter of outlet pipe
- f 1,f 2,f μ,f ε :
-
model functions
- G K :
-
turbulent energy production
- h 0 :
-
outside wall heat transfer coefficient
- h i :
-
inner wall heat transfer coefficient
- H=(D-d)/2 :
-
step height
- k :
-
thermal conductivity
- K :
-
turbulent kinetic energy
- Nu=h i D/k :
-
Nusselt number
- Nu DB :
-
Nusselt number of fully developed pipe flow based on Dittus-Boelter equation
- P :
-
mean pressure
- Pr=μC p /k :
-
Prandtl number
- Pr t :
-
turbulent Prandtl number
- q w :
-
heat flux through pipe wall
- r :
-
radial coordinate
- R=D/2 :
-
radius of outlet pipe
- Re D =UD/v :
-
Reynolds number based on outlet pipe diameter
- Re d =Ud/v :
-
Reynolds number based on inlet pipe diameter
- R t =K 2/(vε) :
-
turbulent Reynolds number
- S Φ :
-
source term of Φ
- S ΦP,S ΦC :
-
source coefficients of Φ
- t :
-
temperature fluctuation
- T :
-
time mean temperature
- T i :
-
mean temperature at the inlet plane
- u i :
-
velocity fluctuation ini-th direction
- U :
-
axial time mean velocity
- U i :
-
time mean velocity ini-th direction
- U c :
-
center line velocity
- U iC :
-
center line velocity at inlet
- U in :
-
average velocity at the inlet plane
- V :
-
radial time mean velocity
- x :
-
axial coordinate
- x i :
-
spatial coordinate ini-th direction
- y :
-
distance from the wall
- y +=C 1/4 K 1/2 y/v :
-
dimensionless distance from the wall
- α t :
-
turbulent thermal diffusivity
- αΦ :
-
under-relaxation factor for Φ
- K=0.41:
-
model constant
- ΓΦ :
-
diffusivity for Φ
- ε:
-
turbulent energy dissipation rate
- ∀:
-
control volume
- μ:
-
dynamic viscosity
- v :
-
kinematic viscosity
- v t :
-
eddy viscosity
- V eff=V+V t :
-
effective viscosity
- σ K , σε :
-
model constants
- Φ:
-
common variable
- δ ij :
-
Kronecker delta
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This work was supported by a Research Challenge Grant sponsored by the Ohio Board of Regents.
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Chung, B.T.F., Jia, S. A turbulent near-wall model on convective heat transfer from an abrupt expansion tube. Heat and Mass Transfer 31, 33–40 (1995). https://doi.org/10.1007/BF02537419
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DOI: https://doi.org/10.1007/BF02537419