An experimental investigation was made of forced convection filmboiling of subcooled water around a sphere at atmospheric pressure.The water was sufficiently cool that the vapor condensed before leavingthe film with the result that no vapor bubbles left the film. The experimentalruns were made using inductively heated spheres at temperaturesabove 740°C. and using inlet water temperatures between15°C. and 27°C. The spheres used had diameters of 1/2 inch, 9/16inch, and 3/8 inch and were supported by the liquid flow. Reynoldsnumbers between 60 and 700 were used.
Analysis of the collected non-condensables indicated that oxygenand nitrogen dissolved in the water accumulated within the vapor filmand that hetrogeneous chemical reactions occurred at the spheresurface. An iron-steam reaction resulted in more than 20% by volumehydrogen in the film at wall temperatures above 900°C. At temperaturesnear 1100°C. more than 80% by volume of the film was composedof hydrogen. It was found that gold plating of the sphere could eliminatethis reaction.
Material and energy balances were used to derive equations whichmay be used to predict the overall average heat transfer coefficientsfor subcooled film boiling around a sphere. These equations includethe effect of dissolved gases in the water. Equations also were derivedwhich may be used to predict the composition of the film forcases in which an equilibrium exists between the dissolved gases andthe gases in the film.
The derived equations were compared to the experimental results.It was found that a correlation existed between the Nusselt numberfor heat transfer from the vapor-liquid interface into the liquid andthe Reynolds number, liquid Prandtl number product. In addition,it was found that the percentage of dissolved oxygen removed duringthe film boiling could be predicted to within 10%.
