Changes in steam temperature after pressure reduction
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Saturated steam is transported through a dn50 pipe (at a pressure of 0.4 Mpa and a temperature of 140 degrees). It then enters a stand-alone control valve, where the pipe diameter is changed to dn100 and the pressure is reduced to 0.07 Mpa. The steam enters via a dn100 pipe at the bottom of a 42-cubic-meter tank; there is a dn100 open-type outlet at the top of the tank. Question: 1. What is the temperature after the steam is depressurized? 2. If gas supply continues, what will be the temperature and pressure inside the tank?
After the saturation steam is depressurized, temperature and pressure correspond to each other. With the gas supply pressure remaining constant, the temperature and pressure inside the tank stay unchanged once they have stabilized.
If no humidification occurs after the saturation steam is depressurized, the temperature resulting from the depressurization will be higher than the saturation temperature corresponding to that pressure; for example, when the pressure is reduced from 0.4 MPa to 0.1 MPa, the temperature is approximately 130°C.
Regarding the heat retention effect, in an ideal situation with no heat loss, it should be 140 degrees. After depressurization, it is superheated steam. The actual temperature is lower than 140 degrees
At a pressure of 0.4 Mpa and a temperature of 140 degrees, it is unsaturated steam (the saturation temperature for steam is 151.8 degrees). When the pressure is reduced to 0.07 Mpa using isenthalpic reduction, the temperature of the steam becomes 115.2 degrees.
This post was last edited by myface on 2021-8-27 at 17:15. How is it calculated? Should the volume be taken into account?
Isenthalpic calculation, without considering heat loss.
After pressure reduction, it becomes superheated steam. Many answers have been given above, but the insulation downstream cannot be in an airtight state; it is a process in which the superheated steam gradually turns into saturated steam. Whether it will end up as saturated steam depends on the heat loss in the system downstream – if the system is large, then…
This process can be approximated as a throttling expansion process, meaning that the enthalpy value of the water vapor remains constant before and after this process. Although the calculation screenshot below is for a flow control orifice plate, in essence, a flow control orifice plate and a control valve are similar – both are throttling devices. In front of the control valve, there is saturated steam at 0.4 MPa (g), while behind the valve there is superheated steam at 0.07 MPa (g) with a temperature of approximately 138.7°C. Note: This feature is not yet available.
There are many steam calculation software programs available online, and this calculation is independent of volume.