ABSTRACT
Laminar Mixed Convective and Radiative Heat Transfer
in an Inclined Rotating Rectangular Duct with Centered
Elliptic Core
A numerical study of laminar forced and free convective and radiative heat
transfer in an inclined rotating rectangular duct with a centered elliptic core is
reported for a thermally and hydrodynamically fully developed flow. The two heat
transfer mechanisms of convection and radiation are treated independently and
interactively. The coupled equations of momentum and energy transports are
solved using Gauss-Seidel iteration technique subject to given boundary
constraints. Two cases of thermal boundary conditions are considered; CASE I:
The surface heat flux in the flow direction is uniform while the surface
temperature remains uniform around the periphery at a flow cross-section (UHF);
CASE II: The surface temperature of the wall is uniform in the direction of the fluid
flow (UWT). A unique method of spatial discritization is employed to solve the
problem associated with near boundary grid points. Results for local, mean and
total mean Nusselt numbers for various values of Reynolds number, Re; Rayleigh
number, Ra; Geometric ratio, GM; Aspect ratio , RH; Radiation –Conduction
parameter, ζ; Optical thickness, τ; Rotational Reynolds number , Ro and
Emissivity, ε are presented. For the range of parameters considered, radiation and
rotation enhance heat transfer. Results indicate an optimum total mean Nusselt
number when the geometric ratio is 0.84. For a situation when the central core is
a circular duct, the heat transfer from the circular surface is greater than that of
the rectangular surface. For a centered elliptic geometry of e = 0.866, the heat
transfer from the elliptic surface is only greater than that of rectangular surface
when the geometry ratio is within the range 0.2≤GM≤ 0.72. Also, there is
tendency for the flow to transit into turbulent if the rotational Reynolds number,
Ro is greater than 250. The parameter ranges of 0.2≤GM≤ 0.84 and 0≤PeRa ≤ 7.3 x
105 demarcate the region of validity of the numerical solution.
An experimental investigation was conducted for the case of non-rotating and
non radiating configuration only due to limitations in facilities. Experimental
results, using water as the heat transfer fluid, compare favourably with the
corresponding numerical results to within nine percent margin for a given set of
parameters.
Student: Adegun, Isaac Kayode
Supervisor: Prof. B.F. Bello-Ochende
Date: 19th September, 2001
Matric Number: 84/7771