Questions about saturated steam
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It’s actually a matter of definition; I’ve always had doubts about this. For example, when methanol vapor leaves the equipment, its temperature is 450 degrees, and after being cooled in a waste heat boiler, the boiler produces saturated steam at 0.45 MP! The question is regarding the saturated gas as defined in the terminology: when gas and liquid are in equilibrium, the gas is called a saturated gas and the liquid is called a saturated liquid. But here there is only gas – how can we determine whether it is saturated or not? This issue has been puzzling people for many years
It refers to a gas in a saturated state; once the temperature or pressure drops below a certain level, it changes from a gas to a liquid, and vice versa
Don’t you have a level control for the water in your waste heat boiler? How can it be all gas (water vapor)?
But a saturated state should be an equilibrium state; how can there be only a gas phase and no liquid phase? According to gas-liquid equilibrium, liquid must precipitate
So this state of separating the gas from the liquid must be unstable, right? They will surely reach equilibrium with each other again?
This is just the problem statement used to calculate heat, and there seems to be no liquid mentioned in it; otherwise, the mass used in the energy conservation calculation would be that of the liquid that has not yet vaporized. It’s strange to think that saturated steam consists only of gas – if that’s the case, then this state should be quite unstable, right?
Isn’t a gas that is not in a saturated state called saturated vapor? By measuring the corresponding temperature at the saturated steam pressure, it can be determined whether it is saturated or not.
It is of course a state of dynamic equilibrium; the steam produced in the boiler is saturated steam, containing both gas and liquid, with the gas on top and the liquid below. The steam exits the boiler through pipes that provide good insulation, resulting in minimal heat loss, and thus the equilibrium is disturbed to a small extent. However, water will inevitably condense, so steam pipes are equipped with drain pipes at regular intervals to remove the water
So what is a saturated state? A state is considered saturated only when gas and liquid are in equilibrium; the gas is a saturated gas and the liquid is a saturated liquid. How can a state with just one of these conditions be called saturated?
In other words, the gas-liquid mixture that has reached an equilibrium state is actually in an unstable condition once separated; liquid will continue to precipitate. It’s just that with good insulation, heat loss is reduced, so less liquid separates out. But I wonder, if the saturated steam that emerges is adiabatic with no heat loss, shouldn’t liquid also precipitate out theoretically? What is the difference between saturated steam and steam that is not saturated? Is it the temperature or something else?
The gas you see is actually vapor, which contains both liquid and gas. How can you see gas? Steam is not vapor