Advanced micro-fin tubes for condensation

R-22 condensation data are presented for new micro-fin geometries applied to the inner surface of 15.88 mm outside diameter tubes. The purpose of the work was to develop internal geometries having higher condensation coefficients than existing single-groove micro-fin designs. The new geometries include both single-helix and cross-grooved surfaces. The single-groove geometries have 74-80 internal fins, 0.35 mm fin height, and 30 degrees fin included angle. The cross-groove geometrics are formed by applying a second set of grooves at the same helix angle, but opposite angular direction as the first set. Data are provided for varying second groove depths. Data are reported for condensation at 24.0 degrees C in a 2.44 m long test section for 45-181 kg h(-1) mass flow rate. The data show that the heat transfer coefficient increases with the helix angle, up to the maximum 27 degrees tested. The cross grooved tubes provided higher condensation coefficients than the single-helix geometries. The performance of the new geometries are compared to a single-helix geometry (MX(TM)-15) similar to existing micro-fin tubes. The best cross-grooved tube provided 27% higher condensation coefficient than the single-helix tube. The pressure drop is 6% higher than in the single helix tube.