Environmental Engineering Reference
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fer in enclosures, the inclusion of waviness parameters of walls, as amplitude and
wavelength, could become important to model realistic conditions.
In recent years, studies of external natural convection from wavy walls have
been investigated to analyze waviness parameters on heat transfer and fluid flow.
Ashjaee et al. (
2007
) studied the natural convection heat transfer from a constant
temperature wavy wall and computed local heat transfer coefficients using the Mach-
Zehner interferometer. Experimental measurements were carried out for amplitude-
wavelength ratios of 0
10
5
to 5
×
10
5
. Numerical results from a finite-volume based code were successfully compared
with experimental measurements. The average heat transfer coefficient decreases
as the amplitude-wavelength ratio increases. Additionally, experimental data were
fitted to a single equation which gives the local Nusselt number along the wavy
surface as function of the amplitude-wavelength ratio and the Rayleigh number. A
thermal convection from a more complex wavy surface is found when a combination
of two sinusoidal functions occurs, a fundamental wave and its first harmonic (Molla
et al.
2007
). Using transformed coordinates on the boundary layer equations yields
a mapped regular and stationary computational domain to evaluate the wavy wall
effect. The additional harmonic alters the flow field and temperature distribution
near the vertical wavy surface. Prescribed heat flux along wavy surfaces have been
investigated solving the boundary layer equations for unconfined flows (Tashtoush
and Abu-Irshaid
2001
). According to the specific amplitude and wave length a point
of separation appears restricting the solution. Additionally, the wavelength of the
local Nusselt number and surface temperature variation were found to be equal to
those of the wavy surface. On the other hand, the wavelength of the average Nusselt
number was a half of that on the wavy surface.
Wavy surfaces are also frequently involved with mass transfer. Effects of com-
bined buoyancy forces due to concentration and thermal gradients from a vertical
wavy surface have been analyzed for unconfined flows focusing on the evolution
of the surface shear stress, the heat transfer, and surface concentration gradient
(Hossain and Rees
1999
). Wide ranges of the governing parameters have been con-
sidered such as Schmidt numbers ranging from 7 to 1,500, amplitude of the waviness
from0 to 0.4, and the buoyancy parameter ranging from0 to 1. The wavywall reduces
the heat transfer, concentration gradient and shear stress. The effect of the inclination
angle has been studied for laminar thermal convection from a constant temperature
wavy wall in a square cavity (Dalal and Das
2004
). For the case of a square cavity
differentially heated through a hot wavy wall, the mean Nusselt is lower than that
corresponding to the flat wall square cavity (Adjlout
2001
). Turbulence improves the
convection heat transfer on the wavy wall surface compared to the case of a square
cavity with high Rayleigh numbers, and different from laminar flow, the presence of
the wavy wall increases the local Nusselt number (Aounallah et al.
2006
). Previous
analysis regarding transport phenomena from wavy walls include the steady flow
and solute uptake in a wavy-walled channel (Woollard et al.
2008
) and the effect of
variable viscosity and variable thermal conductivity on the magneto-hydrodynamics
and the resulting local skin friction, and local Nusselt and Sherwood numbers
.
05, 0
.
1 and 0
.
2, and Rayleigh numbers from 2
.
9
×
.
8
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