The term subcooling refers to a liquid existing at a temperature below its normal boiling point. If the temperature of the liquid is lower than the saturation temperature for the existing pressure, it is called either a subcooled liquid or a compressed liquid. If a water exists as a liquid at the saturation temperature and pressure with quality of x = 0, it is called a saturated liquid state (single-phase). The saturated liquid curve is the curve separating the subcooled liquid state and the two-phase state in the T-s diagram.The saturation vapor curve is the curve separating the two-phase state and the superheated vapor state in the T-s diagram.on the border of vapor/liquid phases), specifying temperature alone will set the pressure and specifying pressure will set the temperature. The terms liquid and vapor tend to lose their significance.Īs can be seen from the phase diagram of water, in the two-phase regions (e.g. Vaporization and condensation can occur only when the pressure is less than the critical pressure. At all states there would be only one phase. In this case, there would be no change in phase from liquid to steam. Consider the behavior of the system which is heated at the pressure, that is higher than the critical pressure. This classification of steam has its limitation. It must be added, at x=0, we are talking about saturated liquid state (single-phase). From this point of view, we distinguish between three basic types of steam. Although defined as a ratio, the quality is frequently given as a percentage. The value of the quality ranges from zero to unity. The mass fraction of the vapor in a two-phase liquid-vapor region is called the vapor quality (or dryness fraction), x, and it is given by following formula: But these parameters will not define the volume and enthalpy because we will need to know the relative proportion of the two phases present.
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As can be seen from the phase diagram of water, in the two-phase regions (e.g.