Abstract:
Experimental and numerical investigations were carried out on
air-filled cavities containing heated inner cylinders.
The effect of varying the position of radial spacers on a
single cylinder was studied. It was concluded that for central
positioning of the cylinder within the cavity. the rate of
heat-transfer was minimised at a radial spacer angle of 480
(measured from the vertically downwards radius vector). When
the cylinder was positioned at displacement ratio of 0.7, the
rate of heat-transfer was minimised at a corresponding spacer
angle of 520. The corresponding reductions in the total rate
of heat-transfer were found to be 25% and 31% less than that
obtained for the system with no spacers at a cylinder
displacement ratio of zero.
Following this research investigation, the behaviour of a
two-pipe arrangement, consisting of a hot supply and cooler
return pipe within a rectangular sectioned cavity, was
studied. Eccentric positioning of both supply and return pipes
showed that minimum rates of heat-transfer occur at supply and
return pipe displacement ratios of 0.45 and -0.33
respectively. This value of heat-transfer is approximately 20%
less than that obtained for a system where supply and return
pipe displacement ratios are 0.7 and zero respectively.
As experimental testing has proved to be excessively time
consuming (e. g. due to having to wait until a steady-state
ensued before measurments were taken) and laborious, a
finite-element numerical model was developed and used to
predict the heat-transfer between a heated inner cylinder and a
cooled outer square duct.
This study investigated eccentricity effects on the rate of
heat-transfer for different ratios of duct height to cylinder
radius. Solutions were obtained for Rayleigh numbers 1 to 300
and optimal pipe eccentricity for minimum heat-transfer was
predicted. These predictions were in good agreement with
previous experimental results.