Wärme - und Stoffübertragung

, Volume 17, Issue 2, pp 85–92 | Cite as

Turbulent heat-transfer characteristics along the heated convex wall of a rectangular cross-sectional return bend

  • N. Seki
  • S. Fukusako
  • M. Yoneta


The turbulent heat-transfer characteristics along the heated convex wall of a return bend which has rectangular cross section with large ratio have been examined for various clearances of the duct in detail.

The experiments are performed under condition that the convex wall is heated at uniform heat flux while the concave wall is insulated. Water as a working fluid is utilized. Using four kinds of clearances of 15, 40, 60 and 80 mm, the Reynolds number in the turbulent range is varied from 8×103 to 8×104 with Prandtl number ranging from 6.5 to 8.5.

In consequence, it is found that both the local and the mean heat-transfer rates are always smaller than those for straight parallel plates or for the straight duct. It is also found that the local heat-transfer characteristics in the outlet region of the return bend are more sensitively influenced by the variation of duct clearance than those in the inlet region.


Heat Flux Reynolds Number Prandtl Number Working Fluid Uniform Heat Flux 
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.



clearance of duct


specific heat at constant pressure


Dean number, [ū·(2c)/ν] √/c/R


hydraulic diameter of duct


centrifugal force per unit volume,ρ2/R)


mean heat-transfer rate, defined in Eq. (3)


local heat-transfer rate atx, q/Δt


mean Nusselt number,hm δ (2c)/λ


mean Nusselt number over inlet region, defined in Eq. (5)


mean Nusselt number over outlet region, defined in Eq. (6)


local Nusselt number based ond e ,h x δd e /λ


Nusselt number of hydrodynamically and thermally fully developed flow


Prandtl number, μδ cp


uniform heat flux from convex wall


radius of curvature of center line of passage in return bend, R o + c/2


Reynolds number, ūδ (2c)/ν


Reynolds number based ond e ,ūδd e /ν


local Reynolds number, ūδ x/ν


radius of curvature of convex wall


Stanton number, ax/ρūc p


local temperature on convex wall atx


uniform inlet temperature


general wall temperature


temperature difference,T-T in


fluid mean velocity


width of duct


streamwise coordinate along convex wall with origin at beginning of heating


coordinate perpendicular tox


nondimensional distance to determine mean Nusselt number

Greek symbols


angle of advance of convex wall taken from inlet


thermal conductivity of fluid


coefficient of viscosity of fluid


kinematic viscosity of fluid


density of fluid


implicit function to determineh m


(1/2)Re(Re/De)0.2[1 + (Re/De)1/4]Pr0.47


Re 1.2 De −0.2 Pr 0.47


Re 1.45 De −0.45 Pr 0.47



condition based on hydraulic diameter


inlet of return bend (Θ = 0 ∼ π/2)


outlet of return bend (Θ=π/2∼ π)

condition of hydrodynamically and thermally fully developed straight flow

Turbulente Wärmeübertragung längs einer beheizten Wand eines Umkehrkrümmers mit rechteckigem Querschnitt


Es wird der turbulente Wärmeübergang längs der beheizten konvexen Wand eines Umkehrkrümmers mit rechteckigem Querschnitt und großem Verhältnis Breite zu Höhe bei verschiedenen Höhen untersucht. Die konvexe Wand war mit konstanter Wärmestromdichte beheizt, die konkave war isoliert. Arbeitsfluid ist Wasser. Für die vier Kanalhöhen 15, 40, 60 und 80 mm liegen die Reynolds-Zahlen zwischen 8 δ 103 und 8 δ 104, die Prandtl-Zahlen reichen von 6,5 bis 8,5. Die gemessene lokale und mittlere Wärmeübertragung ist immer kleiner als jene zwischen parallelen Platten oder im geraden Kanal. Die lokale Wärmeübertragung im Austrittsbereich des Umkehrkrümmers ist empfindlicher gegen Änderungen der Kanalhöhe als jene des Einlaßbereichs.


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Copyright information

© Springer-Verlag 1983

Authors and Affiliations

  • N. Seki
    • 1
  • S. Fukusako
    • 1
  • M. Yoneta
    • 1
  1. 1.Department of Mechanical EngineeringHokkaido UniversitySapporoJapan

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