Effect of Vapour Velocity on Condensation of Ethylene Glycol on Horizontal Integral Fin Tubes: Heat Transfer and Retention Angle Measurements

Abstract

Heat-transfer data are reported for forced-convection filmwise condensation of ethylene glycol flowing vertically downward over two single, horizontal instrumented integral-fin tubes and one plain tube. Vapor-side, heat-transfer coefficients were obtained by direct measurement of the tube wall temperature using two specially manufactured, instrumented tubes with thermocouples embedded in the tube walls. Both tubes have fin height of 1.6 mm and fin root diameter and 12.7 mm, with fin thickness and spacings of 0.3 mm and 0.6 mm, respectively for one of the tubes and 0.5 mm and 1 mm, respectively for the other. Tests were performed at low pressures; 5.59kPa, 8.15kPa and 11.23kPa, at nominal vapour velocities from 13m/s to 82 m/s. All the data show that both of the finned tubes provided an increase in heat flux at the same vapour-side temperature difference with increasing vapour velocity. Visual observations were made and photographs obtained of the fluid retention angle φf at each combination of vapor velocity and pressure tested. It was observed that the curvature of the meniscus was distorted by the increase in vapor velocity and in many cases, the extent of condensate flooding decreased compared to its value in the quiescent vapor case.