Pengujian Karakteristik Perpindahan Panas Dan Faktor Gesekan Pada Penukar Kalor Pipa Konsentrik Dengan Sisipan Pita Terpilin Berlubang

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 a classic twisted tape insert and perforated twisted tape inserts. Test section was the single pass concentric tube heat exchanger with inner tube and outer tube made of aluminum. Dimensions of outer tube; outer diameter of 21.87 mm and inner diameter of 20.67 mm, and dimensions of inner tube, outer diameter of 15.84 mm and inner diameter of 14.34 mm. The length of heat exchanger was 2,000 mm and the length of pressure drop measurement in the inner tube was 2,010 mm. Flows in the inner tube and in annulus was counter flow. Working fluid in the inner tube was hot water which its inlet temperature was maintained at 60°C, whereas in the annulus was cold water at 28oC. Both of classic twisted tape insert and perforated twisted tape insert with a twist ratio of 4.0 were made of aluminum strips with a thickness of 0.76 mm and width of 12.61 mm which it was twisted so forming twist with the length of pitch was 50.35 mm. Perforated twisted tape inserts were varied with holes diameter of 4 mm and 6.5 mm, respectively, where the distance between the center holes of 4 cm. Twisted tape insert installed in the inner tube of the concentric tube heat exchanger. The results showed that at the same Reynolds number, the addition of classic twisted tape insert and perforated twisted tape insert with holes diameter of 4 mm and 6,5 mm in the inner tube increasing the average Nusselt numbers were 79,20%, 68,7%, and 57,8% than the inner tube without a twisted tape insert (plain tube), respectively. At the same pumping power, the average Nusselt number in the inner tube with the addition of perforated twisted tape inserts with holes diameter of 6.5 decreased 1.62%, whereas the addition of perforated twisted tape inserts with holes diameter of 4 mm classic twisted tape inserts increased the average Nusselt number were 3.2% and 5,84% compared with plain tube, respectively. At the same Reynolds number, the addition of classic twisted tape inserts and perforated twisted tape insert with holes diameter of 4 mm and 6,5 mm in the inner tube increased the average friction factor 339.25%, 298.49% and 269.6% than plain tube, respectively. At the same pumping power, the addition of classic twisted tape inserts and perforated twisted tape insert with holes diameter of 4 mm and 6.5 mm in inner tube increased the average friction factor 485.39%, 416.48 % and 362.72% than plain tube, respectively.

Keywords : Nusselt number, Reynolds number, friction factor, perforated twisted tape insert