Fu, Wen-Lung (2005-05). Aspect ratio effect on heat transfer in rotating two-pass rectangular channels with smooth walls and ribbed walls. Doctoral Dissertation.
This study experimentally investigates the effects of rotation, the buoyancy force,
and the channel aspect ratio on heat transfer in two-pass rotating rectangular channels.
The experiments are conducted with two surface conditions: smooth walls and 45??
angled ribbed walls. The channel aspect ratios include 4:1, 2:1, 1:1, 1:2 and 1:4. Four
Reynolds numbers are studied: 5000, 10000, 25000 and 40000. The rotation speed is
fixed at 550 rpm for all tests, and for each channel, two channel orientations are studied:
90?? and 45?? or 135??, with respect to the plane of rotation. Rib turbulators are placed on
the leading and trailing walls of the channels at an angle of 45?? to the flow direction. The
ribs have a 1.59 by 1.59 mm square cross section, and the rib pitch-to-height ratio (P/e)
is 10 for all tests.
The effects of the local buoyancy parameter and channel aspect ratio on the
regional Nusselt number ratio are presented. Pressure drop data are also measured for
both smooth and ribbed channels in rotating and non-rotating conditions. The results
show that increasing the local buoyancy parameter increases the Nusselt number ratio on
the trailing surface and decreases the Nusselt number ratio on the leading surface in the
first pass for all channels. However, the trend of the Nusselt number ratio in the second
pass is more complicated due to the strong effect of the 180?? turn. Results are also
presented for this critical turn region of the two-pass channels. In addition to these
regions, the channel averaged heat transfer, friction factor, and thermal performance are
determined for each channel. With the channels having comparable Nusselt number
ratios, the 1:4 channel has the superior thermal performance because it incurs the least
pressure penalty. In this study, the author is able to systematically analyze, correlate, and
conclude the thermal performance comparison with the combination of rotation effects
on five different aspect ratio channels with both smooth walls and rib turbulated walls.