Condensation of Ethylene Glycol on Integral-Fin Tubes: Effect of Fin Geometry and Vapor Velocity

Abstract

New experimental data are reported for forced-convection condensation of ethylene glycol on a set of nine single, copper, integral-fin tubes. The first set of five tubes had fin height and thickness of 1.6 and 0.25mm, respectively, with fin spacings of 0.25, 0.5, 1.0, 1.5, and 2.0mm. The second set of four tubes had fin spacing and thickness of 1.0 and 0.5mm, respectively, and fin heights of 0.5, 0.9, 1.3, and 1.6mm. The fins were rectangular in cross section. All tubes had a fin root diameter of 12.7mm. A plain tube of outside diameter 12.7mm was also tested. The tests, which were performed at a near constant pressure of ∼15kPa, covered vapor velocities between 10 and 22m∕s and a wide range of heat fluxes. The best performing tube was that with fin spacing, height, and thickness of 0.5, 1.6, and 0.25mm, respectively, which had an enhancement ratio (compared to the plain tube at the same vapor-side temperature difference and vapor velocity) of 2.5 at the lowest vapor velocity tested, increasing to 2.7 at the highest. For all but two of the tubes, the effect of vapor velocity on the heat-transfer coefficient of the finned tubes was less than on the plain tube, leading to a decrease in enhancement ratio with increasing vapor velocity. For two of the tubes, however, the enhancement ratio increased with increasing vapor velocity, which is the opposite trend to that found in most earlier experimental studies. This effect was thought to be due to the slight reduction in condensate flooding between the fins of these two tubes because of vapor shear.