Miscellaneous Mechanical Components
Pressure exerted on the surface of a liquid by a vapor is called vapor pressure. Vapor pressure
increases with the temperature of the liquid until it reaches saturation pressure, at which time
the liquid boils. When a liquid evaporates, it loses its most energetic molecules, and the average
energy per molecule in the system is lowered. This causes a reduction in the temperature of the
Boiling is the activity observed in a liquid when it changes from the liquid phase to the vapor
phase through the addition of heat. The term saturated liquid is used for a liquid that exists at
its boiling point. Water at 212oF and standard atmospheric pressure is an example of a saturated
Saturated steam is steam at the same temperature and pressure as the water from which it was
formed. It is water, in the form of a saturated liquid, to which the latent heat of vaporization
has been added. When heat is added to a saturated steam that is not in contact with liquid, its
temperature is increased and the steam is superheated. The temperature of superheated steam,
expressed as degrees above saturation, is called degrees of superheat.
The pressurizer provides a point in the reactor system where liquid and vapor can be maintained
in equilibrium under saturated conditions, for control purposes. Although designs differ from
facility to facility, a typical pressurizer is designed for a maximum of about 2500 psi and 680F.
A dynamic pressurizer serves to:
maintain a system's pressure above its saturation point,
provide a means of controlling system fluid expansion and contraction,
provide a means of controlling a system's pressure, and
provide a means of removing dissolved gasses from the system by venting the
vapor space of the pressurizer.
A dynamic pressurizer is constructed from a tank equipped with a heat source such as electric
heaters at its base, a source of cool water, and a spray nozzle. A spray nozzle is a device
located in the top of the pressurizer that is used to atomize the incoming water.