PhDFor condensation on horizontal low-finned tubes, the
dependence of heat-transfer performance on fin spacing has
been investigated experimentally for condensation of
refrigerant 113 and ethylene glycol. Fourteen tubes have
been used with inside diameter 9.78 mm and working length
exposed to vapour 102 mm. The tube had rectangular
section fins having the same width and height (0.5 mm and
1.59 mm) and with the spacing between fins varying from
0.25 mm to 20 mm. The diameter of the tube at the fin root
was 12.7 mm. Tests were also made using a plain tube
having the same inside diameter and an outside diameter
equal to that at the root of the fins for the finned tubes.
All tests were made at near atmospheric pressure with
vapour flowing vertically downward with velocities of 0.24
m/s and 0.36 m/s for refrigerant 113 and ethylene glycol
respectively. Optimum fin spacings were found at 0.5 mm
and 1.0 mm for refrigerant 113 and ethylene glycol
respectively. In earlier experiments for steam using the
same tubes, the optimum fin spacing was found to be 1.5 mm.
Maximum enhancement ratios of vapour-side heat-transfer
coefficient (vapour-side coefficient for a finned tube /
vapour-side coefficient for a plain tube. for the same
vapour-side temperature difference) were 7.5, 5.2 and 3.0
for refrigerant 113, ethylene glycol and steam
respectively.
Enhancement phenomena have also been studied
theoretically. Consideration has been given to a role of
surface tension forces on the motion and configuration of
condensate film. On the basis of this study, several
semi-empirical equations, to predict heat-transfer
performance, have been obtained. These are considered to
represent recent reliable data (present and other recent
works) satisfactorily
