Experimental and numerical studies for natural convection in two dimensional
regions formed by a constant flux heat horizontal elliptic tube concentrically located
in a larger, isothermally cooled horizontal cylinder were investigated. Both
ends of the annulus are closed. Experiments were carried out for the Rayleigh
number based on the equivalent annulus gap length ranges from 1.12x107 up to
4.92x107; the elliptic tube orientation angle varies from 0o to 90o and the hydraulic
radius ratio, HRR, was 6.4. These experiments were carried out for the
axis ratio of an elliptic tube (minor/major=b/c) of 1:3. The numerical simulation
for the problem is carried out by using commercial CFD code. The effects of the
orientation angle as well as other parameters such as elliptic cylinder axis ratio
and hydraulic radius ratio on the flow and heat transfer characteristics are investigated
numerically. The numerical simulations covered a range of elliptic tube
axis ratios from 0.1 to 0.98 and for the hydraulic radius ratios from 1.5 to 6.4. The
results showed that the average Nusselt number increases as the orientation angle
of the elliptic cylinder increases from 0o (the major axis is horizontal) to 90o (the
major axis is vertical) and with the Rayleigh number as well. Also, the average
Nusselt number decreases with the increase of the hydraulic radius ratio. An increase
up to 1.75 and further increases in the hydraulic radius ratio leads to an
increase in the average Nusselt number. The axis ratio of the elliptic cylinder has
an insignificant effect on the average Nusselt number. Both the average and local
Nusselt number from the experimental results are compared with those obtained
from the CFD code.
Both the fluid flow and heat transfer characteristics for different operating and
geometric conditions are illustrated velocity vectors and isotherm contours that
were obtained from the CFD code. Also, two correlation equations that relate the average Nusslet number with the Rayleigh number, orientation angle, and hydraulic
radius ratio and axis ratio are obtained. |
