| dc.description.abstract | Accurate and repeatable heat-transfer data are reported for forced-convection filmwise
condensation of steam and ethylene glycol flowing vertically downward over two
single, horizontal instrumented integral-fin tubes and one plain tube. Vapour-side,
heat-transfer coefficients were obtained by direct measurement of the tube wall
temperature using specially manufactured, instrumented tubes with thermocouples
embedded in the tube walls. Both tubes had fin height of 1.6 mm and fin root diameter
of 12.7 mm, with fin thickness and spacing of 0.3 mm and 0.6 mm, respectively for
the first tube and 0.5 mm and 1.0 mm respectively for the second. Tests were
performed at atmospheric pressure for steam with nominal vapour velocities from
2.4 m/s to 10.5 m/s and at three pressures below atmospheric with nominal vapour
velocities from 8.4 m/s to 57 m/s for steam and 13 m/s to 82 m/s for ethylene glycol.
The data show that both the finned tubes provide 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 condensate retention angle
at each combination of vapour velocity and pressure. It was observed that the
curvature of the meniscus was distorted by the increase in vapour velocity and in
many cases, the extent of condensate flooding changed compared to its value in the
quiescent vapour case.
In parallel, experiments involving simulated condensation on finned tubes were
conducted using horizontal finned tubes in a vertical wind tunnel. Condensate was
simulated by liquid (water, ethylene glycol and R-113) supplied to the tube via small
holes between the fins along the top of the tube. Downward air velocities up to 24 m/s
were used and retention angles were determined from still photograph. Eight tubes
with a diameter at the fin root of 12.7 mm were tested. Five tubes of which had fin
height of 0.8 mm and spacing between fins of 0.5 mm, 0.75 mm, 1.0 mm, 1.25 mm
and 1.5 mm and three tubes had fin height 1.6 mm with fin spacings 0.6 mm, 1.0 mm
and 1.5 mm. The results were repeatable on different days and suggested, for all tubes
and fluids, that the retention angle asymptotically approached a value around 80o to
85o (from either lower or higher values at zero vapour velocity) with increase in air
velocity. Good agreement was found with observations taken during the condensation
experiments. | en_US |
