Abstract
The problem of buoyancy driven turbulent flow in parallel-plate channels is investigated. The investigation is limited to vertical channels of uniform cross-section with different modes of heating. The details of the flow and thermal fields are obtained from the solution of the conservation equations of mass, momentum, and energy in addition to equations of the low Reynolds number turbulence model. The study covers Rayleigh number ranging from 105 to 107 and focuses on the effect of channel geometry on the characteristic of the flow and thermal fields as well as the local and average Nusselt number variation. A Nusselt number correlation has been developed in terms of a modified Rayleigh number and channel aspect ratio for the cases of symmetrically heated isothermal and isoflux conditions.
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Abbreviations
- b :
-
Half channel width
- C P :
-
Specific heat at constant pressure
- C 1ɛ, C 2ɛ, C μ :
-
Empirical constants in the k − ɛ turbulence model
- D :
-
Extra term in Eq. 6
- E :
-
Roughness parameter
- f 1, f 2, f μ :
-
Wall damping function
- g :
-
Gravitational constant
- g i :
-
Component i of the gravitation vector
- G b :
-
Production of turbulent kinetic energy due to buoyancy
- G k :
-
Production of turbulent kinetic energy due to mean velocity gradient
- Gr :
-
Grashof number = gβb 3(T w − T o)/ν2
- h :
-
Average heat transfer co-efficient
- h y :
-
Local heat transfer coefficient
- κ:
-
Thermal conductivity
- k :
-
Kinetic energy of turbulence
- L :
-
Channel length
- Nu y :
-
Local Nusselt number
- \(\overline{{\hbox{Nu}}} \) :
-
Average Nusselt number
- P :
-
Pressure
- Pr:
-
Prandtl number
- Prt :
-
Turbulent Prandtl number
- Ra:
-
Rayleigh number = (Gr·Pr)
- Ram :
-
Modified Rayleigh number = Ra(b/L)
- R y :
-
Local Reynolds number = k 1/2 y/ν
- T :
-
Temperature
- \(\overline{T} \) :
-
Dimensional temperature
- T o :
-
Ambient temperature
- T s :
-
Channel wall (surface) temperature
- u, v :
-
x- and y-components of velocities, respectively
- \(\overline{u}, \;\overline{v} \) :
-
Time-averaged x and y components of velocities, respectively
- u i :
-
ith component of velocity
- x, y :
-
Cartesian coordinates
- α:
-
Thermal diffusivity
- β:
-
Co-efficient of thermal expansion
- ε:
-
Rate of dissipation of the kinetic energy
- μ:
-
Laminar viscosity
- μt :
-
Turbulent viscosity
- ν:
-
Molecular kinematic viscosity
- θ:
-
dimensionless temperature [=(T − T o)/(T w − T o)]
- ρ:
-
Density
- σ k :
-
Prandtl number for k
- σɛ :
-
Prandtl number for ɛ
- avg:
-
Average
- i :
-
ith component
- o:
-
Ambient
- \(\overline{{\;\;\;}}\) :
-
Time-average value
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Acknowledgements
The authors would like to acknowledge the support received from King Fahd University of Petroleum and Minerals during the course of this study.
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Badr, H.M., Habib, M.A., Anwar, S. et al. Turbulent natural convection in vertical parallel-plate channels. Heat Mass Transfer 43, 73–84 (2006). https://doi.org/10.1007/s00231-006-0084-z
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DOI: https://doi.org/10.1007/s00231-006-0084-z