INTRODUCTION

The steam that enters the turbine steam path has a high-energy content. In fossil-fueled cycles, this steam is normally superheated, i.e., the steam contains a degree of heat in excess of that required to completely evaporate it. On expansion, this superheat is released in the steam path, converting its thermal potential energy to kinetic energy in the rotor. When all the superheat has been converted to kinetic energy, further expansion causes the remaining dry, saturated steam to give up a portion of its latent heat, which is converted to water. The flow then becomes a two-phase mixture of steam and water.

However, in the water-cooled nuclear cycle and in the majority of geothermal cycles, steam that enters the high-pressure section contains some small amount of moisture. This moisture portion of the mixture is increased throughout the initial stages of the expansion and the majority of the low-pressure stages.

Once water has formed, it must be removed or transported through the steam path by the parent steam. Because of the relatively larger mass of the moisture particles, they are unable to pass through the blade passages with the same degree of acceleration as the dry steam. These water particles must have work done upon them in an attempt to match steam velocities.

These steam velocities will act upon the water particles because the steam accelerates and changes direction in the blade passages. However, the water particles will be unable to accelerate and achieve velocity equality because of their larger...