Questions about saturated steam?
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What state is the water at saturated vapor pressure in after pressure reduction? For example, water at 150 degrees temperature and 0.5 MPA pressure (saturated water) – when the pressure is reduced to 0.1 MPA – is it in the form of water vapor, water, or both? Will the temperature drop at this time? Is what comes out water at 120 degrees and 0.2 MPa, saturated water and saturated steam (assuming that the temperature may not change by that much)?
After pressure reduction, low-pressure steam can be generated, but not in excess of a certain amount; there is still some water present, and the temperature is naturally that of the steam at that pressure.
This requires an analysis of the specific circumstances. As a closed system, if there is no heat exchange with the surrounding environment at the interface, then it can be analyzed as follows: For saturated water, when the pressure remains constant, the amount of heat inside the closed system is fixed. When the pressure decreases, the vaporization temperature also drops. Thus, there is a difference in heat between saturated water at high pressure and that at low pressure. What is done with this difference in heat? It is first used for the vaporization of the saturated water under reduced pressure (as latent heat of vaporization). Depending on the magnitude of this heat difference, three scenarios arise: First, there is a mixture of water and steam, when the heat difference is not sufficient to vaporize all of the saturated water. Second, the entire volume consists of steam, that is, when the heat difference is just enough to convert all the saturated water into steam at the same pressure. Third, it results in superheated steam, when the heat difference is sufficient to vaporize all the saturated water with some excess remaining.
If saturated steam at 0.5 MPa is throttled to 0.1 MPa, and the enthalpy of the steam remains unchanged during this throttling process, then the steam becomes superheated steam, with a temperature lying between the saturation temperatures corresponding to 0.5 MPa and 0.1 MPa.