Pengujian Karakteristik Perpindahan Panas Dan Faktor Gesekan Pada Penukar Kalor Pipa Konsentrik Saluran Annular Dengan Twisted Tape Insert With Oblique Teeth

Abstract

Abstract :This research was conducted to examine the characteristics of heat transfer and friction factor in the annular channel concentric tube heat exchanger with the addition of twisted tape insert with oblique teeth. Test section was the single pass concentric tube heat exchanger with inner tube and outer tube made of aluminum. The length of heat exchanger was 2,110 mm and the length of pressure drop measurement in the inner tube was 2,240 mm. Flows in the inner tube and in annulus were counter flow. Working fluid in the inner tube was hot water which its inlet temperature was maintained at 60°C, whereas the working fluid in the annulus was cold water with its inlet temperature of ± 28oC. For comparison, inner tube tested without twisted tape insert (plain tube) and with the addition of twisted tape insert without oblique teeth (classic twisted tape insert). Classic twisted tape insert and twisted tape insert with oblique teeth made of aluminum strip with a thickness of 0.7 mm width 12.6 mm, which had a twist ratio of 4.0 and the pitch length of 50.3 mm. While the twisted tape inserts with oblique teeth varied with tooth angle of 15°, 30° and 45°. Classic twisted tape insert and twisted tape inserts with oblique teeth installed in the inner tube of the concentric tube heat exchanger  The research result has showed that the inner tube with the addition of twisted tape insert with oblique teeth produce Nusselt number, friction factor and thermal performance that was greater than the addition of classic twisted tape insert and plain tube. Values of Nusselt number, friction factor and thermal performance increase with the increase in tooth angle of twisted tape inserts with the oblique teeth. At the same Reynolds number, the addition of twisted tape insert with oblique teeth with a tooth angle 15°, 30°, and 45° resulting in an increased average Nusselt number in the inner tube, of 61.8%, 75.3% and 89.2% when compared to the plain tube, respectively. Compared to classic twisted tape inserts, inner tube with twisted tape inserts with oblique teeth with a tooth angle 15°, 30°, and 45° experienced increase Nusselt numbers, an average of 10.2%, 19.4% and 28.9%, respectively. At the same Reynolds number, the addition of classic twisted tape insert and twisted tape insert with oblique teeth with a tooth angle 15°, 30°, and 45° in the inner tube has produced an average friction factor of 2.4; 2.9; 3.4; and 3.9 times than the friction factor of plain tube, respectively. The average thermal performance with the addition of classic twisted tape inserts, twisted tape inserts with oblique teeth with a tooth angle 15°, 30°, and 45° in the inner tube of 1.003; 1.060; 1.106; and 1.151 respectively.

Keywords : Nusselt number, Reynolds number, Twisted tape insert with, oblique teeth, Tooth angle