Film condensation of steam on low-integral finned tubes with drainage strips

Abstract

Heat-transfer measurements were made for filmwise condensation of steam under low pressure and at near-atmosphere pressure on horizontal finned tubes attached with bronze porous and solid drainage strips. The effect of drainage strip type, height and thickness were investigated. A total of 16 drainage strips were manufactured and tested on two finned tubes each with a fin thickness and height of 1.0 mm and with a fin spacing of 0.5 mm and 1.0 mm. The heat-transfer performance generally increased with increasing porous strip height up to a possible optimum value between 11 and 15 mm. Of the pore diameters tested (0.05-0.013 mm, 0.025-0.05 mm, and 0.0025-0.05 mm), the strip with an average pore diameter of 0.025-0.05 mm gave the best heat-transfer performance. This optimum strip type showed an optimum strip thickness of 5.2 mm. The solid strips showed an optimum strip thickness of 1.5 mm. The optimum porous strip gave a 9% and 1% greater steam-side enhancement than the optimum solid strip for low and atmospheric pressures, respectively. For the finned tube with a fin spacing of 0.5 mm, a maximum enhancement of about 2.6 was found when it was attached with a 5.2-mm-thick and 8-mm-high porous strip having a pore diameter of 0.025-0.05 mm.