Heat transfer enhancement during R-404A vapor condensation in swirling flow

In the present study, an experimental investigation has been performed to examine the heat transfer enhancement achieved by twisted tape inserts during forced convective condensation of R-404A vapor inside horizontal tubes. The test section was a coaxial double-pipe counter-flow heat exchanger where R-404A flowed in the inner tube and coolant water flowed through the annulus. Four full-length twisted tapes with twist ratios of 4, 7, 10 and 14 were used on the refrigerant side of test-condenser. Experiments were carried out for plain tube and twisted tape inserted tubes at five R-404A mass velocities for each tube. Investigation of the results showed that employing twisted tape inserts inside tube increases the average heat transfer coefficient up to approximately 50% above the plain tube values. Moreover, a performance evaluation for the twisted tape inserted tubes was accomplished. (C) 2012 Elsevier Ltd and IIR. All rights reserved.