During the temperature and pressure reduction process, when the pressure is reduced, if the temperature remains unchanged, how does the pressure decrease?

Through the throttle valve, the temperature of the medium does not drop instantly, but the expansion pressure after throttling can decrease immediately; as a result, superheated steam may be generated, which can be cooled by adding water to turn it into saturated steam

Sir, is it the conservation of mass or the conservation of amount of substance that applies before and after pressure reduction? If mass conservation means that the volume flow rate increases during expansion, then does the pipe need to become thicker after pressure reduction? Also, from my understanding, since the pressure decreases but the temperature cannot decrease, if the temperature remains unchanged then the saturated vapor pressure also remains unchanged. If the amount of substance does not change, this is impossible; therefore, it must be that the amount of substance decreases later on, is that right?

The laws of conservation of mass and energy are not violated in any applications by scientists, unless nuclear physics is involved; in nuclear fission and fusion, mass is lost, and according to the equation E=mC^2, there is a conversion between matter and energy. The application of physical laws requires consideration within a specific system – if one examines only a part of that system, taking things out of context will lead to many misunderstandings. It is possible to draw diagrams on paper; by listing the states of all materials in the system, things will become clear. Otherwise, one can only rely on speculation and arguments. When the flow area of a throttle valve is small, the gas flow velocity is high. After throttling, the volume increases and the gas expands, resulting in a decrease in pressure. However, the number of molecules and the mass remain unchanged, and the temperature does not drop sharply. After spraying water, the temperature drops, and the sprayed water vaporizes to produce saturated steam with a pressure lower than that of the gas source

This post was last edited by Qingcheng Jun on 2019-2-18 at 10:52. The volume increases after expansion, but the volumetric flow rate, measured in Nm3, remains unchanged. After throttling, the state is unsaturated, and temperature and pressure do not follow the calculations for saturated vapor pressure. In the phase diagram of water, the red line represents the saturated vapor pressure curve. Before throttling, the steam is at a point on this red line; during throttling, the temperature remains constant while the pressure drops, and the state of the steam changes as it moves vertically downward from the red line to become superheated steam. After water is sprayed in, the pressure stays the same while the temperature drops, and the state of the steam shifts horizontally to the left, intersecting the red line to form new saturated steam