Condensation of refrigerants on vertical fluted tubes

Experiments were run to determine heat transfer performance of single vertical fluted tubes with selected fluids condensing on the outside. Working fluids included six fluorocarbons (Refrigerants 11, 21, 22, 113, 114, and 115) and a hydrocarbon (Refrigerant 600a or isobutane). The nine test tubes were of 2.54-cm nominal outside diameter and 1.2 m in length with from 0 (smooth) to 60 axial flutes. Condensing heat transfer coefficients ranged from 620 to 7900 W/sq m K over the heat flux range of 2000 to 43,000 W/sq m. All parameters are based on total condensing surface area. The data show that, for a given heat flux, a fluted tube can increase condensing coefficents up to 6.0 times smooth tube values. Further heat transfer enhancement was achieved by the use of drainage skirts on fluted tubes; these skirts effectively divided the 1.2-m tubes into two, four, and eight equal condensing lengths.