Eli5: How hot would water have to be for it to be vapor coming out of the tap?
In: Physics
Water can become vapor at virtually any temperature, even if it’s solid ice. But it sounds like you’re imagining a faucet spewing nothing but steam. I’m not sure how that would work exactly plumbing-wise, but I suspect the whole system (including any water fed into it) would have to be boiling (100 °C or 212 °F). Under normal circumstances (i.e outside of a pressurized vessel or something), you can’t really get water hotter than that.
For water to be hot enough inside the pipe under pressure and become steam when it exits into an environment with normal pressure, it would need to have a temperature of 641°C.
If it already was steam inside the pipe, lower temperatures would be enough. The exact temperature depends on the pressure difference between inside and outside the pipe. If there was no pressure difference, 100°C would be enough.
Explanation:
Water needs to absorb 2260 Joule per gram to transition from “Water at 100°C” to “Steam at 100°C”. Water also needs 4.18 J per gram to increase by 1°C in temperature. If you prevent water from turning into steam with pressure, those 2260 Joule would be enough to heat it up by 541°C.
However, there is one little caveat. 641°C is right in the range where water cannot be a liquid anymore. You’re getting some weird super-critical fluid that is neither and both steam and water. You also need a really sturdy pipe to get there, we’re talking about pressures way above 220 bar/3200psi.
A hundred degrees centigrade, the boiling point of water. (edit: give or take, depending on air pressure/altitude.) If you heat water up past its boiling temperature, it is forced to evaporate, and it’s impossible for it to continue existing as a liquid.
But this fact can be a bit deceiving, because pretty much whenever you have liquid water at any temperature, *some* of it is always evaporating into the air. The exact rate of evaporation depends on the temperature, and depends on the humidity – i.e. how much vapor is already present in the air.
So, even when the water faucet is running cold, a *little bit* of it will be coming out as vapor, but in order for it to be 100% vapor, it needs to be boiling hot.
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