Effect of Helical Screw Tape Insertion on Heat Transfer and Pressure Drop Characteristics in a Horizontal Concentric Double Tube Heat Exchanger

Abstract

In the present work, the effects of insertion of helical screw tape on heat transfer characteristics and pressure drop in a concentric double tube heat exchanger are experimentally investigated. The heat exchanger has the outer (steel) and inner (copper) tube diameters of 50 mm and 25 mm respectively. The helical screw tape of diameter 19 mm is inserted into the inner tube to increase turbulence which helped to increase the heat transfer rate. The hot water was flowed through the inner tube and cold water was flowed in annulus. The helical screw tape was inserted in 1/3rd length and full length of the tube. The experiments are based on Reynolds number at tube inlet, ranging from 10000 to 42855. The experimental results show that the average Nusselt numbers and friction factors are respectively, 1.41 and 2.08 times over the plain tube for 1/3rd length insert and 1.87 and 4.31 times over the plain tube for full length insert. Furthermore, the enhancement ratio of the helical screw tape varies between 1.03 and 1.17, 1.02 and 1.26 for 1/3rd length insert and full length insert, respectively.