Ym. Zhang et al., HEAT-TRANSFER AND FRICTION CHARACTERISTICS OF TURBULENT-FLOW IN CIRCULAR TUBES WITH TWISTED-TAPE INSERTS AND AXIAL INTERRUPTED RIBS, Journal of enhanced heat transfer, 4(4), 1997, pp. 297-308
Local heat transfer distributions and pressure drop in smooth circular
tubes with twisted-tape inserts and axial interrupted ribs were inves
tigated. Experimental data for isothermal friction factors and regiona
lly averaged Nusselt numbers are presented for turbulent air flows for
Reynolds numbers ranging from 17,000 to 82,000. The circular tube is
composed of ten isolated copper sections with a tube length-to-diamete
r ratio (L/D) of 15. Three different 360 degrees twisted-tape ratios a
re studied: H/D = 6(2.5 turns), 7.5 (2 turns), and 10 (1.5 turns). Thr
ee axial interrupted rib configurations attached to the inner wall of
three test tubes with twisted-tape inserts are investigated: e/D = 0.0
625 in-line rib, e/D = 0.0625 staggered rib, and e/D = 0.125 staggered
rib. The results show that the heat transfer and pressure drop in the
tube with twisted-tape inserts increase by increasing the number of t
wisted-tape turns. The tube with twisted-tape inserts provide 1.5-2.0
times the heat transfer augmentation with 3-4 times the pressure drop
penalty. The tube with twisted-tape inserts and staggered ribs produce
higher heat transfer and pressure drop than that with twisted-tape in
serts and in-line ribs, and significantly higher than without ribs. Th
e tube with twisted-tape inserts (H/D = 7.5) and e/D = 0.125 staggered
ribs provides 1.8-2.8 times the heat transfer enhancement with about
9-10 times the pressure drop penalty. The tube with twisted-tape inser
ts (H/D = 6) and with staggered ribs (e/D = 0.125) gains 2.2-3.2 times
the heat transfer while paying 13-14 times the pressure drop. The bes
t heat transfer performance in the tube with twisted-tape insert and s
taggered ribs (e/D = 0.125) is about 25-40% higher than that with the
twisted-tape only for different H/D for a constant pumping power.