CONDENSATION COEFFICIENT AND WETNESS THERMAL LOSSES OF WET STEAM FLOW AT LOW PRESSURES

Condensation coefficient of wet steam flow at low pressures has been
evaluated theoretically. It was found from the theoretical results th&t wet
steam condensation coefficient depends upon: the pressure at ~ilson
point, vapour supercooling, droplet sue, evaporation coeffkieht' and
.4 index of isentropic expansion.
Available data on the condensation coefficient of wet steam flow
through nozzles are found to be dependent on the pressure values of both
initial flow conditions and Wilson point. A comparison has been
conducted between the present values of the condensation coefficient and
that reported and required to minimize the difference between the
predicted and measured pressure distributions in wet steam flow through
nozzles. The agreement in the comparison is good. In order to verify the
model, another comparison between a measured pressure distribution
and a predicted one through a nozzle based on selected values for the
condensation and evaporation coefficients is also carried out. 'The quality
of agreement in this comparison is good.
Moreover, entropy increase due to the irreversibility of heat and mass
transfer proceses in wet steam has been estimated numerically. The
numerical results show that increasing the condensation coefficient,
droplet size and expansion rate as well as decreasing the evaporation
coefficient tends to increase the wetness thermal losses during wet steam
flow.