One more thing: adding hot water, which evaporates faster, will probably increase vapor pressure in the environment, slowing down, or even stopping evaporation.
this post was submitted on 24 Mar 2024
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More info needed. Does all the water need to evaporate, or just the original stuff?
You could add extremely hot steam and get a universal yes, but the way this is worded makes me think it has to be liquid.
All of it.
I never thought about steam. I guess the amount of pressure needed to persuade steam to mix with standing water would prevent evaporation.
Let's assume you're in complete control of the surrounding environment, pressure, gas mixture etc, and can change them at will during the experiment.
I mean, if you can create a vacuum, water at any temperature will boil-freeze. And the ice will sublimate afterwards above cryogenic temperatures, but I'm not sure how fast.
Even if you don't mix the steam with the water, heat will seep in through the surface. At thousands of degrees you bet that water is gone fast - explosively - as long it's not super deep. If this is for drying something, you can add a bunch of other hot inert gasses to dilute or push it out after, so when you cool everything back down it doesn't re-condense.
If you have to add liquid water, it might be impossible, although I can't say for sure there isn't some weird non-linear evaporation effect that allows it to technically work on very cold water. Intuitively, you are always adding more additional water than additional heat, but water is crazy and breaks usual rules for matter fairly often. I'll do a bit of digging and edit.
Edit: Research turned up nothing. As far as I can tell, water evaporation is calculated as being a linear rate. Like the light thing someone else posted, that doesn't necessarily mean there isn't a counterexample, just that it hasn't been found and publicised well enough for a quick search around. So yeah, no wetting away a puddle.
Aw man, finally a sort of appropriate question for me to drop this relatively new knowledge: you don't even need heat to evaporate water, light is enough. Scientific finding from last year!
Sorry, you may not have needed to know, but more people should know about this!
Not exactly relevant but cool nonetheless.
Huh. It's always neat when we discover something basic, but overlooked.
Not by adding the hot water to the cold.
But if you can use the hot water to heat up the cold water a little bit, that can help. That would mean bringing them into thermal contact but not allowing them to mix.
Bonus question. What will freeze faster: a cup of 100 ml hot water or 100 ml cold water? Both are uncovered.
Oh no, not the ~~mbappe~~ Mpemba effect effect. I refuse to accept that as a real thing, there is just no way the warm water freezes faster. I've read dozens of articles about it, eventually finding some that confirmed for me it's probably just measuring error or subtle differences that aren't being noticed. But that left me thinking if I had to search so hard for the one article that confirms my gut instinct I shouldn't lean into it too hard
Like you have two cups of identical water, eventually the warm water becomes the cold water. If I then use that previously warm water as my cold water and start the experiment over with another glass of warm water, what now? And don't tell me water has memory.
My favorite explanation is imagine two cars on a track 100 meters long. The far end is the track is hard asphalt and cars can drive fast. The track gets rougher and muddier the closer you are to the finish line, so the first 50 meters are covered in seconds, the next 25 meters are slower, and the final 5 meters the cars are crawling. You start one car at the 100 meter line and one starts at 10 meters. If you're observing this race from the top of a 50 storey building above the track, you'd understandably think "wow, that car that started far away was so much faster! For sure it won" even though in the last few feet it was neck-and-neck.
mbappe effect
You read dozens of articles and aren't even close to spelling his name right?
You just cut his name into a thousand pieces and there's blood everywhere.
Ahhh damn! I was about to board a plane and didn't bother googling it, mixed him up with the footballer
I had a chuckle thinking about the mbappe effect being researched by Hanson, Hanson, and Hanson.
The reason the hot one freezes first is because the hot one evaporates more, thereby lowering it's mass. The amount of energy that must be removed from water to cool it is small compared to the amount of energy to freeze the water. Therefore, the mass of the water that freezes determines the total energy much more strongly than the starting temperature.
Actually, it doesnt exist.
Previous experiments accounted for evaporation by using sealed containers, and still observed mpemba phenominon.
A recent-ish study managed to control factors for all the proposed reasons of the mpemba phenominon, and found no difference between freezing cold and hot water.
They found the location of the temperature probe to be more of a factor than anything else.
https://youtu.be/SkH2iX0rx8U
Essentially, any observations of this can be accounted for by margins of error.
So in isolation, hot water does not freeze faster than cold water.
Any observation of this are from environmental effects (extra nucleation sites in the water, different freezing conditions etc).
So the laws of thermodynamics still hold.
However, what these environmental factors are and how they contribute arent yet understood.
That's what I'm talking about! That's for digging that up. It just never passed the smell test for me, I always called bs
Thanks for the video. As it notes, the observations are real, but the explanation may not be known.
However, preventing the evaporation and then finding that the process does not occur kind of proves the evaporation theory, so I'm not sure that point works the way that you or Derek claim it does, unless I'm misunderstanding.
Lastly, I'm not claiming nor do I believe that there is some mystical way of violating the laws of thermo. I'm claiming that when the mass of water is reduced that the total latent heat is also reduced; that is completely consistent with thermo.
I'm curious what prompted this question. Why not just evaporate the hot water if your goal is evaporating water?
Just curious. There's no real world scenario. This is not c/askEngineering.
It would mostly depend on surface area available then. If you can add warmer water and also increase the surface area available to evaporate, then you could evaporate it faster
Maybe there's standing water somewhere that they're wanting gone
Go out there with a blow dryer or heat gun I guess lol. Adding more water isn't gonna help you get rid of all the water. But I was curious if it was just a homework problem or what lol
I think even just moving air increases evaporation rate.
No need to waste energy on heat, just a fan will do
Yeah, I have no idea, that's just the only real-life scenario I could think of lol
No. Unless that hot water is very, very hot vapor, you're just adding more mass that's going to be cooled by the original cold water. And even with vapor, the heat transfer between a hot gas and cool liquid just doesn't happen fast enough, the vapor will be in the atmosphere before the water heats up very much.
Yeah you're better off heating up the existing water without adding more volume.