Saturation Vapor Curve
See also: Steam
As can be seen from the phase diagram of water, in the two-phase regions (e.g. on the border of vapor/liquid phases), specifying temperature alone will set the pressure and specifying pressure will set the temperature.
- The saturation vapor curve is the curve separating the two-phase state and the superheated vapor state in the T-s diagram.
- The saturated liquid curve is the curve separating the subcooled liquid state and the two-phase state in the T-s diagram.
Typically most of nuclear power plants operates multi-stage condensing steam turbines. In these turbines the high-pressure stage receives steam (this steam is nearly saturated steam – x = 0.995 – point C at the figure) from a steam generator and exhaust it to moisture separator-reheater (point D). The steam must be reheated or superheated in order to avoid damages that could be caused to blades of steam turbine by low quality steam. High content of water droplets can cause the rapid impingement and erosion of the blades which occurs when condensed water is blasted onto the blades. To prevent this, condensate drains are installed in the steam piping leading to the turbine. The reheater heats the steam (point D) and then the steam is directed to the low-pressure stage of steam turbine, where expands (point E to F). The exhausted steam is at a pressure well below atmospheric, and is in a partially condensed state (point F), typically of a quality near 90%.