An experimental study on condensation heat transfer characteristics of R-600a in tubes with coiled wire inserts

In this experimental research, condensation heat transfer enhancement of R-600a as a consequence of used spring inserts inside a horizontal condenser is studied. The condenser was a copper tube with the internal diameter, wall thickness, and length of 8.1, 0.71, and 1000 mm, respectively. Five coiled wires with various coil pitches of 10, 20 and 30 mm, and various wire diameters of 0.5, 1 and 1.5 mm were used inside the test pipe. Tests were conducted at vapor qualities within the range of 0.03-0.79 and mass velocities between 115-365 kg/m2s. Results indicated that coiled wires are advantageous instruments in heat transfer improvement of the condenser. In this regard, the coiled wire with the wire diameter of 1.5 mm and coil pitch of 10 mm showed the best performance among all inserts by the heat transfer coefficient increased up to 107% over the smooth tube. It was also observed that the use of springs affects the transition of flow pattern from annular to intermittent, and the annular regime was observable at a lower vapor quality in comparison to the smooth tube. Finally, a new correlation is developed to predict the condensation heat transfer coefficients of R-600a in coiled wire inserted tubes.