This is awesome. Basically it separates the water into two layers, with a sort of a filter of black plastic. The plastic has holes that are optimized such that you get a layer of hot water up top that evaporates easily, but that still allows the movement of salt to prevent the buildup of a really salty brine. Neat, elegant.
> Based on their calculations, a system with just 1 square meter (about a square yard) of collecting area should be sufficient to provide a family’s daily needs for drinking water, they say. Zhang says they calculated that the necessary materials for a 1-square-meter device would cost only about $4.
If true -- this could be utterly transformative for much of the world.
> We did not build a family scale prototype, such as 10 sq ft. It would be some efforts for us to scientifically test that scale one with existing testing setups, mostly due to the limiting size of our solar simulator. Our existing waterjet cannot handle that size as well. A tank to work with will be 100L at least for our testing.
If it cost $4 to build and was at all practical to use, the claim that it is odious to do so would make no sense. As we're led to believe it does make sense, I have trouble believing it costs $4 and that it is practical to use with such a budget.
"families needs" is deceptive. There is plain simple drinking water, but that's a tiny amount compared to that needed for washing, farming, and all other uses for water.
For example, a person in the USA uses 4 tons of water per day! Yet under 0.05% of that is drunk.
You have salt water. You heat up the water. Water evaporates off the top, condenses somewhere, the condensed water is clean drinkable fresh water. The stuff that's left is brine, which is essentially a waste product.
The engineering question is how much water do you use? You could use a thick later, like a swimming pool. But that takes a lot of energy to heat up. You could use a thin layer, like an inch thick across a parking lot. This takes less heat energy, but a lot of energy to clear out the brine, and a lot of salt will build up that you will need to periodically need to clean out.
This thingie does the best of both worlds. It is a thin layer at the top. Thin is good, because it takes less energy to heat. The layer between them is insulated, so you don't lose heat energy to the pool of water below it. There are channels between them that transports water upwards and salt downward via convection.
The thin layer at the top heats and evaporates quickly. The salt is transported fairly rapidly past the insulated boundary and into the large pool below. The large pool supplies more water through the same boundary.
The large pool can be slowly mixed with the ocean.
I'm kinda blown away by this. What a shockingly ingeniously simple and effective mechanism. It's like when I learned that the guts of a normal coffee machine that makes coffee machines do coffee machine things is just a heater, a hose, and a one way ball valve, and literally nothing else.
I hope it works and I hope it scales. We could be done with California's drought problem in a decade.
This system isn't attempting to innovate on the condenser. The condenser part is the solved problem part of a water purifier; it's generally just a sheet of plastic or glass.
very nice direct approach, do have questions about the diameter of the holes they
choose (1/8-inch) versus the thickness of the barrier layer.
also
the reservoir below will have to be significant enough that increasing the salinity below does not adversely change the buoyancy of the floating insulation with the convection holes enough to make the evaporation layer above too thin.
that is; in the closed system shown the insulation will float higher as the water is evaporated eventually self limiting
Interesting approach. I wonder why it takes so long to validate this? Given it's simplicity, you could prototype a system pretty easily and cheaply, I imagine.
Making millions of tiny holes is hard so it's a manufacturing and engineering issue. Sometimes physics gets on the way when you scale a small prototype.
- Salt water is poured into a reservoir that is exposed to the sun.
- The salt water evaporates due to the heat from the sun.
- Leaving the salt behind (and most other impurities), the water vapor rises until it lands on the glass and condenses into water droplets.
- After enough builds up on the glass, gravity pulls the water droplets down the glass until they drop into a separate reservoir - not exposed to the sun. This water is desalinated and drinkable
It's efficient, cheap, slow, space consuming, simple and works well.
