101–110 of 205 posts
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Given the agricultural issues in that movie, perhaps the purification device was intended more to collect and concentrate the urea than to purify the water. But that assumes the scriptwriter would have thought of that, which may be a stretch, given that Earth has insufficient water to cover all landmasses to a depth of 7 km. That would require about 3.6 billion cubic kilometers more water than already exists in the o…
So the only possible explanation of the cause of the Waterworld apocalypse is earth being hit by millions of giant ice meteors.
But on the other hand, society had collapsed along with most of the stored knowledge of the world, so maybe it was just the people being uneducated and highly insular. They don't even know how long a kilometer is anymore.
There was a point in history a few hundred million years ago where the entire American midwest was a shallow water ocean; we could easily be heading back to that scenario in just a few centuries.
"than 1.5 gallons of fresh drinking water per hour for every square meter of solar collecting area." Units, people. Units. Be imperial. Be metric. Hey! Be both!
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> 1 billion gallons of water per day * How much of that water need be drinkable? * How much of that water can be salinated (e.g. for flushing)? * How much of that water can be partially desalinated (e.g. for showering)?
This doesn't matter as NYC is built on a river that provides plenty of fresh water every year. It needs to be treated and filtered, but at much less cost than desalination.
In any event, NYC gets its water from upstate, not locally: https://en.wikipedia.org/wiki/New_York_City_water_supply_sys...
The combination of hydrogen production and desalination using simple techniques are an exciting prospect for this decade. For architects of 21st century cities, most of these sustainable technologies would benefit from a cleanslate design, rather than trying to compete with builtup 20th century infrastructure. I think Austrailia is postured to be the biggest beneficiary of all of these "leaps" in technology this cent…
Landships sound like the plot of some dystopian future film; ecosteaders fight off the scavenger bands.
Cities like Detroit and other areas past their prime did not devolve into madmax scenes, but instead are left with a bunch of toxic funk floating in a cesspool.
Definitely not somewhere you'd want to settle down.
This is a well-known approach known as multistage flash distillation: https://en.wikipedia.org/wiki/Multistage_flash_distillation It's surprising they didn't mention this in the article. (It is, of course, mentioned in the paper, because its authors are decent and honest people.) > more than 1.5 gallons of fresh drinking water per hour I don't understand. Are those imperial gallons, US gallons, US dry gallons, or Iri…
Imperial and US gallons would both make sense, and you're right it's ambiguous.
Dry gallons would not make sense, since this is a liquid quantity, and Irish gallons are long obsolete.
> 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. I need an explanation with pictures for that, because it seems like the author is using ‘efficiency’ incorrectly.
I would personally define desalination efficiency of 100% as a perfectly-reversible reaction that establishes an equilibrium between fresh water and oceanic salt water.
Since adding sea salt to fresh water until it has oceanic salinity represents a theoretical maximum of 0.810 Wh/L (a maximally efficient osmotic power plant, situated where a river empties into the ocean, could get about 0.75 Wh/L). So 100% efficiency would be adding 0.810 Wh to one liter of seawater to get one liter of fresh water back. 100% is an unachievable goal, thanks to the laws of thermodynamics.
So to figure your solar desalination efficiency, from a solar panel that receives X Wh/m^2/day of insolation energy, you divide by 0.810 Wh/L to get L/m^2/day. Whatever fresh water you can produce per day, divide by that number to get your efficiency.
An MIT roof gets mean 4.59 kWh/m^2/day of solar energy, so 100% efficiency for them would be 4590/0.810 = 5667 L/m^2/day. By the numbers given, their process is about 2% to 3% efficient (by my definition).
They could be a lot more efficient if they didn't have to overcome the huge heat of vaporization that water has, which is exactly why reverse osmosis is so much more efficient than multistage flash distillation. They are stacking so that the evaporation energy can be recovered from the condensation, which deposits the same amount of energy on the next layer, but it's better off all around to just never evaporate in the first place.
>> 1.5 gallons of fresh drinking water per hour for every square meter of solar collecting area. So a football field could collect around 8,000 gallons of water per hour. Let's say you can get 5 hours of good sunlight per day = 40,000 gallons of water. >> 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. >> Theor…
Of course, once we factor in cleaning uses of unsalted water, the picture is less pretty. Still, not bad.
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What's that in bathtubs per football field?
EDITED: bathtub ≈ 302 liters football field = 5351 square meters They achieved 5.78 L/m^2/h So 5351 m^2/football field * 5.78 L/m^2/h = 30928.78 L/h/football field 30928.78 L/h/football field / 302 L/bathtub = 102.4 bathtubs/football field/hour h/t to brudgers for the correction about football field surface area!