PENGUJIAN KARAKTERISTIK PERPINDAHAN PANAS DAN FAKTORudGESEKAN PADA PENUKAR KALOR PIPA KONSENTRIK SALURANudPERSEGI DENGANudFAKULTAS TEKNIK UNIVERSITAS SEBELAS MARETudCLASSIC TWISTED TAPE DAN PERFORATEDudTWISTED TAPE INSERT

摘要

The research was conducted to examine the characteristics of heat transfer andudfriction factor in the rectangular channel heat exchanger with a classic twisted tapeudinserts and perforated twisted tape insert. Test section was the single pass concentricudtube heat exchanger with inner tube and outer tube made of aluminum. The dimensionsudof the outer tube were 23.05 mm x 23.05 mm for the outer side and 21.75 mm x 21.75udmm for the inner side, whereas the dimensions of the inner tube were 18.50 mm x 18.50udmm for the outer side and 17.20 mm x 17.20 mm for the inner side. The length of heatudexchanger was 1,998 mm and the length of pressure difference measurement in theudinner tube was 2,018 mm. Flows in the inner tube and in annulus were in oppositeuddirections. Working fluid in the inner tube was hot water which its inlet temperatureudwas maintained at 60°C, whereas in the annulus was cold water at ± 28oC. Both ofudclassic twisted tape insert and perforated twisted tape insert with a twist ratio of 4.0udwere made of aluminum strips with a thickness of 0.76 mm and width of 12.61 mmudwhich it was twisted so forming twist with the length of pitch was 50.35 mm. Perforatedudtwisted tape inserts I and II were punched with hole diameter of 4 mm and 6.5 mm,udrespectively, where the distance between the center hole of 4 mm. Twisted tape insertudinstalled in the inner tube of the concentric tube heat exchanger.udThe results showed that at the same Reynolds number, the addition of classicudtwisted tape insert, perforated twisted tape insert I and perforated twisted tape insert IIudin the inner tube increasing the average Nusselt numbers were 40.83 %, 16.80%, andud31% than the inner tube without a twisted tape insert (plain tube), respectively. At theudsame pumping power, the average Nusselt number in the inner tube with classic twistedudtape insert, perforated twisted tape insert I, and perforated twisted tape insert II increasedud27.21%, 12.41%, and 15.07% than the plain tube, respectively. At the same Reynoldsudnumber, the addition of classic twisted tape inserts, perforated twisted tape insert I andudperforated twisted tape insert II in the inner tube increased the average friction factorud3.19, 1.89, and 2.71 times than plain tube, respectively. At the same pumping power , theudaddition of classic twisted tape inserts, perforated twisted tape insert I and perforatedudtwisted tape insert II the average friction factor increased 4.51, 1.85, and 3.41 times thanudplain tube, respectively. The average thermal performance of inner tube with theudaddition of classic twisted tape inserts, perforated twisted tape insert I and perforatedudtwisted tape insert II were 1.26, 1.13, and 1.11, respectively.udKeywords : Nusselt number, Reynolds number, classic twisted tape, friction factor,udperforated twisted tape