Miscellaneous Mechanical ComponentsDOE-HDBK-1018/2-93PRESSURIZERSPressure exerted on the surface of a liquid by a vapor is called vapor pressure. Vapor pressureincreases with the temperature of the liquid until it reaches saturation pressure, at which timethe liquid boils. When a liquid evaporates, it loses its most energetic molecules, and the averageenergy per molecule in the system is lowered. This causes a reduction in the temperature of theliquid.Boiling is the activity observed in a liquid when it changes from the liquid phase to the vaporphase through the addition of heat. The term saturated liquid is used for a liquid that exists atits boiling point. Water at 212oF and standard atmospheric pressure is an example of a saturatedliquid.Saturated steam is steam at the same temperature and pressure as the water from which it wasformed. It is water, in the form of a saturated liquid, to which the latent heat of vaporizationhas been added. When heat is added to a saturated steam that is not in contact with liquid, itstemperature is increased and the steam is superheated. The temperature of superheated steam,expressed as degrees above saturation, is called degrees of superheat.GeneralDescriptionThe pressurizer provides a point in the reactor system where liquid and vapor can be maintainedin equilibrium under saturated conditions, for control purposes. Although designs differ fromfacility to facility, a typical pressurizer is designed for a maximum of about 2500 psi and 680F.DynamicPressurizersA 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, andprovide a means of removing dissolved gasses from the system by venting thevapor space of the pressurizer.ConstructionA dynamic pressurizer is constructed from a tank equipped with a heat source such as electricheaters at its base, a source of cool water, and a spray nozzle. A spray nozzle is a devicelocated in the top of the pressurizer that is used to atomize the incoming water.Rev. 0ME-05Page 31
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