PhDAccurate and repeatable heat-transfer data have been obtained for filmwise
condensation from pure vapours (steam and Refrigerant 113) and vapour-gas
(steam-air, steam-hydrogen, Refrigerant 1 13-air and Refrigerant 113-
hydrogen) mixtures flowing vertically downward over single horizontal tubes.
The tube surface could be viewed to ensure that the filmwise mode of
condensation prevailed throughout all tests. Two copper tubes having
diameters 12.5 mm and 25.25 mm were used. Surface temperatures at four
positions were obtained from thermocouples embedded in the tube wall. The
heat flux was obtained from coolant measurements which were checked against
values obtained by condensate collection. The vapour mass flow rate was
obtained from the electrical power input to the boiler. (The mass flow rate
determination incorporated a correction for relatively small 'thermal
losses' to the environment which were established by preliminary measurements
in which all the vapour supplied to the test section was condensed
and. collected. Non-condensing gases could be supplied continuously via
variable-aperture float-type flowmetera to the boiler. The working length
(r11O mm) of the condenser tube was located, centrally in the cylindrical
test section (152.4 mm). The vapour Reynolds number (based on the teat
section diameter) was generally greater than 2000. The mean vapour approach
velocity over the working length was determined on the basis of a 'seventh
power profile' in conjunction with the measured flow rate. The approximate
ranges of the variables used were:- pressure (4 - 124 kpa), heat flux (12
- 466 kW/m2 ), vapour velocit' (0.3 - 26 n/a), gas mole (mass) fraction
(o.i % (0.02 %) - 35 % (32 %)). The vapour-gas combinations were chosen
to give a wide range of Schmidt number (about 0.05 - 0.5).
For pure vapoura, the results are in overall agreement with earlier data
(mostly steam) at moderate approach velocities. While discrepancies exist
at higher velocities, both the present and earlier results show satisfactory
agreement with theory at low and moderate velocities. The vapour-gas data
are in good agreement with the limited earlier measurements (steam-air only)
and with theory. In particular, the theoretically predicted Schmidt number
dependence was clearly established