Indirect measurement of local condensing heat-transfer coefficient around horizontal finned tubes.

Abstract

Heat-transfer measurements were made for condensation of steam on three finned tubes with rectangular-section fins. These tubes have a fin thickness and fin height of 1.0 mm and fin spacings of 0.5, 1.0 and 1.5 mm. Data were taken by insulating both the inner and outer surfaces over up to 5 or 6 angular portions, including 0, 30, 60, 90, 150, 210 degrees, of the top portion of each tube. The measured average heattransfer coefficients for the unblanked portion of the tube were processed to yield both the local and average heattransfer performance as a function of the angle measured from the top of the tube using a third-order polynomial. The results show that the average enhancement for the fin spacings of 0.5, 1.0 and 1.5 mm were 2.5, 3.0 and 3.1,. respectively, for the atmospheric-pressure condition. And they were 1.8, 2.3 and 2.4 for the low-pressure condition. The local enhancements at the top of tubes were 5.2 and 3.8 for s = 0.5 mm, 6.6 and 4.8 for 3=1.0 mm, and 6.6 and 5.5 for s = 1.5 mm at atmospheric and low pressures, respectively.