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Simple, solar-powered water desalination (2020)

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Re: Simple, solar-powered water desalination (2020)

#141

Post by linschn »

ppf wrote: post #77

It's incredibly disappointing to see MIT put its name to some apparently PhD-level research that claims over-unity efficiency, and apparently (according to the picture) using a few baking trays and tinfoil. It also does not explain how to deal with the increased salination of the water source, nor how water can continue to condense on the successive layers of the device as they are heated due to that condensation.

This is for small scale, family-sized units, where power and cost are the limiting factor, so brine will not be an issue at this scale.

As for condensation, the plate is hot, but colder that the vapor, and heated by the vapor only, so when it is too hot, condensation stops, the temperature drops quickly due to evaporation on the other side, and condensation can continue.

At equilibrium, each successive plate is colder than the next, the last one using the sea water as a heat sink.

This is actually innovative and the optimization of the design parameters (e.g. The distance between the plates) is not trivial.

I think you are overly dismissive of this solid piece of engineering.

Re: Simple, solar-powered water desalination (2020)

#142

Post by stephen_g »

trainsplanes wrote: post #101
ComodoHacker wrote: post #98

Earlier quoted context omitted.

It's an example of a good old scientifically flavored clickbait. The energy efficiency of anything cannot exceed 100% (until I missed something groundbreaking in physics).

It very much can exceed 100% and it’s not a measure invented for click bait purposes. Look up heat pumps. You can make things hotter by moving heat than you could by directly heating it by burning fuel.

The ‘more than 100%’ is only in comparison to a less efficient process. A heat pump itself is operating below 100% efficiency - it’s just kind of “cheating” by using an external source of external energy as one of its inputs in addition to the electricity running it.

Re: Simple, solar-powered water desalination (2020)

#143

Post by tonyhb »

betwixthewires wrote: post #138
tonyhb wrote: post #135

Earlier quoted context omitted.

Or maybe we don't have to spread humans everywhere like a malignant cancer, leaving at least these Islands to nature.

Maybe don't spread your Malthusian bullshit like a malignant cancer. Some of us like being human.

Hey, me too! Never said I didn't. Just that it's nice to leave some parts of the world to itself.

Re: Simple, solar-powered water desalination (2020)

#145

Post by creshal »

Chris2048 wrote: post #129
creshal wrote: post #57

Earlier quoted context omitted.

Or is it? > In a free-floating configuration, any salt that accumulates during the day would simply be carried back out at night through the wicking material and back into the seawater, according to the researchers. This is fine for a small scale demonstration unit, but with bigger plants you will again run into the problem of over-salinating seawater, destroying the environment (and reducing your still's efficiency)…

Can salt be compressed and then just buried?

Sure, it's just that in this regard it has no advantage over other desalination technologies. You always have to deal with the excess salt, MIT is dishonest in waving away these concerns.

Re: Simple, solar-powered water desalination (2020)

#147

Post by throwaway894345 »

dystroy wrote: post #115
squarefoot wrote: post #107

FTA: "Unlike some desalination systems, there is no accumulation of salt or concentrated brines to be disposed of. In a free-floating configuration, any salt that accumulates during the day would simply be carried back out at night through the wicking material and back into the seawater, according to the researchers." The capabilities are freaking interesting, but let's say someone builds a big enough settlement on a…

Salt release is already a huge environmental concern with exiting desalinization systems. Energy consumption and installation costs aren't the sole (and probably not the main) problems. Desalinization is inherently a pollution.

Why not release the salt back to the sea? Presumably it would not increase the salt content of the ocean very much considering the vastness of the ocean and the sheer quantity of fresh water that is being added to it by melting glaciers, etc? What am I missing?

Re: Simple, solar-powered water desalination (2020)

#148

Post by lyschoening »

celticninja wrote: post #99
londons_explore wrote: post #82

Earlier quoted context omitted.

'drinking water' often doesn't mean the water a human literally drinks, but all the clean water necessary for living everyday life (bathing, flushing toilets, washing dishes, cleaning clothes, cooking etc.).

I am pretty sure if you had to get your water from one of these devices you would not be using it to flush toilets or other non-essential use. And actually it does seem like 'drinking water' is actually drinking water and not for all those other uses you mentioned. As 3.7 litres is the amount required for a human male each day. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-h...

From Wikipedia:

> Drinking water, also known as potable water, is water that is safe to drink or use for food preparation.

40-50L per day would seem to about cover one person's essential uses of potable water.

Re: Simple, solar-powered water desalination (2020)

#149

Post by dystroy »

throwaway894345 wrote: post #147
dystroy wrote: post #115

Earlier quoted context omitted.

Salt release is already a huge environmental concern with exiting desalinization systems. Energy consumption and installation costs aren't the sole (and probably not the main) problems. Desalinization is inherently a pollution.

Why not release the salt back to the sea? Presumably it would not increase the salt content of the ocean very much considering the vastness of the ocean and the sheer quantity of fresh water that is being added to it by melting glaciers, etc? What am I missing?

The salt you release isn't instantly diluted in the whole ocean and we're speaking, for a plant, of millions cubic meters of salt enriched water per day. The release area is just dying.

Re: Simple, solar-powered water desalination (2020)

#150

Post by raducu »

wcoenen wrote: post #30
crackercrews wrote: post #3

For those curious what the 385% refers to > the team’s demonstration device can achieve an overall efficiency of 385 percent in converting the energy of sunlight into the energy of water evaporation. Honestly I still don't know what that means, or how efficiency can be over 100%.

The 100% level refers to a system where all energy goes to heating up water in order to evaporate it, and then letting it cool down to condense it. All the energy that was spent to heat up the water, is lost to the environment in the "cooling down" step. If some of the heat is instead recovered during condensation to heat up the next batch of water, then you have >100% efficiency.

Does it have to be batches?

Can't it be like the reverse of a rocket engine where they use regenerative cooling from the fuel to cool the rocket nozzle, but just in reverse.

Or like they way my grandpa was doing moonshine -- the alcohol vapors pass through a serpentine in a water tank, condense, at the end you obtain alcohol, the water in the tank gets warmer -- instead, heat water coming from the water cooling tank that is preheated by the vapors of water that is condensing in the serpentine pipe.

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