| dc.description.abstract | Considerable progress has been made in recent years towards
the understanding of the mechanism of heat transfer by condensation
in the presence of non-condensing gases. For the case of laminar
film condensation on a plane vertical, surface and for laminar
flow of the vapour-gas mixture, boundary layer solutions have been
given [22,43,44]. In the present work these are reviewed and
modifications to the approximate solutions are suggested.
Such limited experimental data (for condensation on vertical
flat plates under conditions of free convection) as was available
at the outset of the present study, disagreed widely with theory.
In the present work further careful measurements were made to test
the validity of the theory. The condensing chamber (i.e. the steam
chamber) was large in comparison to the condensing surface and care
was taken to avoid forced convection effects associated with the
vapour supply to the condenser. The vertical test plate was watercooled
and the surface temperature and the heat flux measured by
thermocouples precisely located in isothermal planes at different
depths.
Steam was condensed in the presence of air, argon, neon and
helium. The pressure in all cases was near to atmospheric. Tests
were carried out for a range of gas concentrations and coolant
flow rates. The present results, in general, give good support to
the boundary layer theory, as do other data [44] for air-steam
mixtures at low pressures, published during the course of the present work.
The theoretical solutions available at present (for free
convection conditions) are not valid for the case where the
non-condensing gas has a molecular weight smaller than that of
the vapour (i.e. when the convective motion of the vapour-gas
mixture near the condensing surface is in the opposite direction
to that of the condensate). The present results for steam-helium
mixture were used to obtain a semi-empirical equation for this
situation. | en_US |
