Abstract
International Journal of Heat and Mass Transfer, Elsevier, 2011,
54 (19-20), pp.4220-4234 The present work focuses on the study of mixed convection of a purely viscous
shear-thinning fluid in a horizontal annular eccentric duct. The inner and
outer cylinders are heated with constant and uniform heat flux densities. The
objective of this work is to study the effect of the variation of eccentricity,
rheological behavior of the fluid as well as the thermodependency of the
rheological parameters on the reorganization of the flow and thermal
stratification caused by the buoyancy forces. At the entrance of the heating
zone, the dynamic regime is assumed to be established and the temperature
profile uniform. The conservation equations are solved numerically using a
finite difference method with implicit schemes. A secondary azimuthal flow,
induced by natural convection, develops downstream of the inlet section. This
flow creates a stratification of the thermal field on a given section of the
duct, which intensifies downstream from the entrance. On the other hand, the
decrease in consistency with increasing temperature near the heated walls
produces a centrifugal radial flow towards the walls. The presence of an
eccentricity induces in turn a significant effect on the main dynamic field and
the stratification of the thermal field. Two cases of upward and downward
eccentricity are treated. These show that an upward shift increases the
stratification of the thermal field, while the stratification begins to weaken
from a certain amount of eccentricity in the case of downward shift. This
represents an important result in terms of possible industrial applications. We
may indeed conclude that an appropriate choice of downward eccentricity can
reduce the thermal stratification, observed experimentally in the case of a
concentric heated annular duct [1], when this stratification is undesirable.
The choice of this eccentricity depends on rheological and thermal properties
of the fluid.