I under stand that the lower the air pressure, the lower the boiling point of water. Also, some primitive desalination kits are basically evaporators.
Could you make a really big tank without a bottom and paint it black. Then, submerge it partly in the ocean . Pump the air out of the top. The water would rise up into the tank, a bit, but not all the way.
You wouldn’t need to have a perfect vacuum, just lower the air pressure enough to make boiling easier. Let the sun heat the black tank, and viola, steam.
Collect that steam from the air you are pumping out of the top of your tank, and you’ve got fresh water, right?
Edit: nevermind. Found it on google. Leaving this here to display my shame.
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Leaving this here to display my shame.
Why be ashamed? You had an idea that’s probably never occurred to the majority of the people on this planet, and you asked for validation. A) that’s original thinking and b) that’s the first steps in science: I have an idea, is it reasonable, how can I experiment with it? I think this is a fantastic post!
Self depreciation is a load bearing coping mechanism. I’m not sure I can turn it off.
2meirl
🫂
Yeah, OP didn’t even phrase it like nobody else could have thought of it, which is a frequent pitfall for these kinds of questions. The experts that can give the best answers hate that. It’s implicitly saying their years of study aren’t worth much.
Honestly there is never any shame about sharing what you’ve learned. I didn’t ever think about this and now I’ve learned something. Keep asking questions and searching for answers!
I mean, my last question was about crapping my space pants, so maybe I shouldn’t aim too high, lol.
I laughed pretty hard at this comment! Shoot for the moon, and if you miss, you’ll crap your pants among the stars!
According to your link, this is actually used in big plants:
Vacuum distillation is often used in large industrial plants as an efficient way to remove salt from ocean water, in order to produce fresh water. This is known as desalination. The ocean water is placed under a vacuum to lower its boiling point and has a heat source applied, allowing the fresh water to boil off and be condensed.
Leaving this hear to display my shame.
This is your real shame.
I appreciate you’re help in pointing that out! I know its easy too get lazy and skip proof reading. I went back and changed it so its like it was never they’re! Its the principal of the matter.
i see what you did their
You should have written “you’re” to share the shame.
yes you can do this, however notice: this is wasteful as you have to run pump and heat from steam condensing is not recovered. You can heat up incoming water with condensing steam - this is called vapour recompression distillation. alternatively you can use heat pump to move heat around
You could but the reality is that using a semipermeable membrane and a difference in pressure is more energy efficient.
I could be wrong, but iirc even tho you can boil the water at lower temperature, it still takes the same amount of energy to change phase, so the efficiency gain isnt as spectacular as you might expect.
The energy to change phase, the latent heat of vaporization, does decreases. Enough such that the ambient temperature is able to supply sufficient heat for vaporization (that is, boiling). The latent heat of vaporization is temperature and pressure dependent for most materials.
I do agree that at some point ambient temperature does the job, which is obviously super convenient.
Akshuly, the charts I can find on the subject of enthalpy of vaporization vs pressure say the opposite- it increases at lower pressure
I could have gotten it backwards. Depends on how the system is being defined and which direction the heat is going.
