The developing region was investigated experimentally in this paper for smooth
and ribbed duct to enhance the heat transfer coefficient at equal pumping power constraint
through the flow passage. The mean velocity of air stream varies from about 4 to 18 m/s
corresponding to a range of Reynolds number from 1.62 x 104 to 7.2 x 104, the rib pitch- toheight
ratio (P/e) varies from 10 to 20, the rib height-to channel hydraulic diameter ratio
(e/De) is fixed at 0.081, and the channel length to hydraulic diameter ratio (L/De) is fixed at
18.75. A rectangular channel with an aspect ratio (W/H) of 4:1 ribbed with square ribs is
investigated at different intake shapes (bellmouth, plenum box, and abrupt intakes). The
effects of the different investigated parameters on the local and average static pressure, and
friction factor are studied. For smooth duct with abrupt and plenum intakes, the maximum
static pressure coefficient was found at the reattachment point at about X/De=0.95, while it
was found at X/De=0.17 for bellmouth intake. For ribbed duct the effect of the intake shape
becomes more significant at the entrance region (X/De40,000. Good agreement was found
between the experimental results and [Liou, et. Al., 1992] data for direct comparison of
static pressure for ribbed duct with plenum intake. The experimental correlations of the
average static pressure coefficient (Cpaverage ) for the developing region of a ribbed duct
with different intake shapes are obtained.
Cpaverage = a Re b (P/e) c (1)
The constant coefficients (a, b, c) and the relative error are listed in table 2. Flow
visualization results were carried out to support the measured results and illustrate the flow
characteristics around the intake and the ribs. |
