Properties of Saturated Water and Steam Pressure

Properties of Saturated Water and Steam (Pressure) (continued)... 

After the deaeration, nuclear heating is restarted. First, the reactor power is kept constant at a low level. When the saturation temperature reaches 280°C, the heat exchanger starts. The reactor power is kept constant until the system attains a steady state. Then, the reactor power is raised again while keeping the pump inlet temperature constant (280°C) using the heat exchanger. When the pressure approaches the critical point (22.1 MPa), the physical properties of saturated water and steam get closer, and hence it is difficult to control the water level. The water level control valve is kept closed above 20 MPa. 

Va.por Pressure. Vapor pressure is one of the most fundamental properties of steam. Eigure 1 shows the vapor pressure as a function of temperature for temperatures between the melting point of water and the critical point. This line is called the saturation line. Liquid at the saturation line is called saturated Hquid Hquid below the saturation line is called subcooled. Similarly, steam at the saturation line is saturated steam steam at higher temperature is superheated. Properties of the Hquid and vapor converge at the critical point, such that at temperatures above the critical point, there is only one fluid. Along the saturation line, the fraction of the fluid that is vapor is defined by its quaHty, which ranges from 0 to 100% steam. 

In a uniform heat flux test section, the CHF cannot vary by one variable without affecting another accompanying variable. Figure 5.40 is reproduced from an article by Aladyev et al. (1961). This figure actually indicates the combined effects of pressure and inlet subcooling at a constant exit quality. The CHF occurs at the exit, and the exit enthalpy is kept at saturation. Because the critical flux varies with pressure, the inlet temperature must also vary. Hence the high CHF at low pressure is achieved by means of a low inlet temperature and the favorable physical properties of water and steam under low pressures also help the heat transfer at the corebubble layer interface. 

When you look up a pressure in the first column of Table B.7, you will find just below it in parentheses the boiling point temperature and in Columns 2 and 3 the properties of saturated liquid water and saturated steam at that pressure. If you are at a point in the superheated steam region, you can move all the way to the left to determine the saturation temperature at the same pressure, or the dew point of the superheated steam. 

Coefficients of the equadon of state and of the equation for transport properties are stored for each substance. Parameters of the critical point and coefficients of equations for calculadon of the ideal-gas functions, the saturated vapor pressure and the melting pressure are kept also. The thermal properties in the single-phase region and on the phase-equilibrium lines can be calculated on the basis of well-known relations with use of these coefficients. The system contains data for 30 reference substances monatomic and diatomic gases, air, water and steam, carbon dioxide, ammonia, paraffin hydrocarbons (up to octane), ethylene (ethene), propylene (propene), benzene and toluene. The system can calculate the thermophysical properties of poorly investigated gases and liquids and of multicomponent mixtures also on the basis of data for reference substances. 

The values for vapor pressure, from 0 to 32 F, were calculated from data In the International Critical Tables/ All other values were taken from Harr, Gallagher, and Kell, NBS/NRC Steam Tables, National Standard Reference Data System, 1984, p. 9. Data on specific volumes of saturated water vapor from 0 to 32 F were obtained from Goff, J. A., and Gratch, S-, "Low-Pressure Properties of Water from -160 to 212°F," Heating, Piping, and Mr Conditioning, Vol 18, No. 2, Feb. 1946, pp. 125-136. 

Extensive tables of the viscosity and thermal conductivity of air and of water or steam for various pressures and temperatures are given with the thermodynamic-property tables. The thermal conductivity and the viscosity for the saturated-liquid state are also tabulated for many fluids along with the thermodynamic-property tables earlier in this section. 

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