Experimental Studies of OTEC Heat Transfer Evaporation of Ammonia on Vertical Smooth and Fluted Tubes

摘要

Experiments were run to determine the heat transfer performance of single vertical tubes with ammonia evaporating from a thin falling film on the tube outside. The three aluminum tubes tested were of 2.54-cm (1.0-in.) nominal diameter and 1.22-m (4.0-ft) length; one with smooth internal and external surfaces, one with a smooth inside surface and 48 external flutes, and one with 34 internal and 42 external flutes. The composite evaporation heat transfer coefficients (coefficients that include the resistance of both the evaporating film and the tube wall), based on the total tube outside surface area, ranged from 2720 to 12,020 W/m exp 2 .K (480 to 2120 Btu/h.ft exp 2 . exp 0 F) over the heat load range of 690 to 3990 W (2360 to 13,620 Btu/h). Corresponding composite temperature differences ranged from 1.2 to 5.7 exp 0 K (2.2 to 10.2 exp 0 F). Reflux ratios, the ratio of the ammonia feed rate at the top of the tube to the average evaporation rate, ranged from 1.1 to 12.6 over the ammonia feed rate range of 3 x 10 exp -6 to 15.9 x 10 exp -6 m exp 3 /s (0.05 to 0.25 gpm). The data show that fluted tubes provide little or no enhancement of evaporation-side heat transfer coefficients when compared to evaporation coefficients obtained from a smooth tube. (ERA citation 05:030468)