Handbook of Turbomachinery Second Edition Revised - Ventech!

were superior to both 908 discrete ribs and parallel-angled continuous ribs
and were recommended for internal cooling passage designs. For 608 and
458, parallel discrete ribs had higher ribbed wall heat transfer, lower smooth
wall heat transfer, and lower channel pressure drop than parallel full ribs.
Parallel 608 discrete ribs had the highest ribbed wall heat transfer, and
parallel 308 discrete ribs caused the lowest pressure drop. The heat transfer
and pressure drops in crossed-angled continuous and discrete rib cases were
all lower than those in the corresponding 908 and parallel-angled rib cases.
Crossed arrays of angled ribs had poor thermal performance and were not
recommended. Correlations of Stanton number and friction factor are
provided for turbine-cooling design.
More recent work by Han et al. [76] has studied the effects of ribs with
different configurations and channel orientation on heat transfer for a
rectangular channel with width-to-depth aspect ratio about 2:1. The local
heat-transfer coefficient distribution in a rotating frame is different from
that of a stationary frame. Heat-transfer coefficient patterns in radial
outward flow and radial inward flow conditions show different dependence
on rotation. This is primarily due to the reversal of the Coriolis force acting
on the moving fluid in a rotating flow. The results of this study confirm a
similar heat-transfer effect in a two-pass rotating rectangular channel as is
observed in a two-pass rotating square channel from the previous work. In
general, the rib-roughened surfaces in a rectangular channel perform
similarly to smooth surfaces with increasing rotational speed. However, the
average heat-transfer coefficient magnitude in a rectangular channel with
ribbed wall is much higher than that of the smooth walls. Ribs placed at an
angle to the bulk flow direction induce greater heat-transfer enhancement.
Comparative studies suggest that a 458 parallel rib configuration in a
rectangular channel is more suitable to enhance heat transfer than a 458
cross configuration for both nonrotating and rotating cases. The effect of
channel orientation on heat transfer shows that a 908 channel orientation
has more effect on leading and trailing surfaces than a 1358 orientation due
to rotation. The difference in Nusselt number ratios between trailing and
leading surfaces in a smooth channel is smaller in a 1358 channel orientation
than a 908 channel orientation. Han et al. [77] studied the heat-transfer and
friction performance of a square channel with parallel, crossed, and Vshaped
angled ribs. Nine rib configurations were tested: 908 rib; 608 and 458
parallel ribs; 608 and 458 crossed ribs; 608 and 458 V-shaped ribs; and 608
and 458 A-shaped ribs. The results showed that the 608/458 V-shaped rib
performed better than the 608/458 parallel rib, and better than the 608/458
crossed rib and the 908 rib. The V-shaped rib produced the highest heattransfer
augmentation, while the A-shaped rib generated the greatest
Copyright © 2003 Marcel Dekker, Inc.