Heat transfer augmentation by coiled wire inserts during forced convection condensation of R-22 inside horizontal tubes

In the present work, heat transfer augmentation by coiled wire inserts during forced convection condensation of R-22 inside horizontal tubes has been studied. The test-condenser consisted of four separate coaxial double pipe test sections assembled in series. It was a counterflow heat exchanger where R-22 condensed inside the inner tube by rejecting heat to the coolant water flowing in the annulus. Coiled wires with three different wire diameters of 0.65, 1.0 and 1.5 mm and three different coil pitches of 6.5, 10.0 and 13 mm were made and used in full length of test-condenser. The use of helically coiled wires were found to increase the condensing heat transfer coefficients by as much as 100% above the plain tube values on a nominal area basis. (C) 1998 Elsevier Science Ltd. All rights reserved.