One of the most effective techniques for augmenting in-tube evaporation heat transfer in refrigeration and air conditioning systems is to use internally finned tubes. In this study, the effects of several geometrical parameters of micro-finned tubes were experimentally investigated for single-phase and evaporation heat transfer. Specifically, the geometrical parameters studied were peak shape, valley shape, fin height, number of fins, and spiral angle. Commercial refrigeration and air-conditioning tubes with 3/8 in (9.52 mm) od were tested using refrigerant R-113 in a 39 in (1.0 m) long test section. The mass velocity range was varied from 145,000 lbm/hr•ft² (197 kg/s•m²) to 440,000 lbm/hr•ft² (594 kg/s•m²) while the average quality over the test section varied from 0.15 to 0.85. The system pressure was maintained at about 35 psi (241 kPa).

The average heat transfer coefficient was increased by 30% to 100% (enhancement factors of 1.3 to 2.0) over the reference smooth tube. The maximum increase in pressure drop was about 80%. The tubes were ranked according to their heat transfer and pressure drop performance using a statistical approach. The tube with 70 spiraled fins having a round peak and a round valley resulted in the best heat transfer performance.

Units: Dual