Earlier quoted context omitted.
It comes out to about 0.4 liters per square foot, for those of you who are confused.
Or, let's see... 5.7 millimeters!
(Per day, one assumes...)
Simple, solar-powered water desalination
191–200 of 205 posts
Re: Simple, solar-powered water desalination
#192Earlier quoted context omitted.
I found this video which seems to animate the concept nicely: https://www.youtube.com/watch?v=udffed4Pq3g
That is such an incredibly smart piece of design. A tip of the hat to whom ever thought it up.
Leif J. Hauge
https://www.powershow.com/download/3b604b-ZGQwN/Pressure_Exc...
Read the history, including how the then-current prototype (out of series of improved versions developed over the 12 years it took to get to a market ready design) and all the inventor's personal belongings were lost in the invasion of Kuwait.
Re: Simple, solar-powered water desalination
#193Re: Simple, solar-powered water desalination
#194Earlier quoted context omitted.
One fascinating (well, to me) component of modern RO desalination systems is the rotary pressure exchanger. Such a simple device, but so important. It looks like something from the 19th century, but the base patent was issued in 1988. https://en.wikipedia.org/wiki/Pressure_exchanger
very similar in principle to 10 years younger https://en.wikipedia.org/wiki/Pressure_wave_supercharger
That sounds like it would be a great way to eliminate the EGR system on vehicles as well if there was a way to vary the relative speed of the rotor to the crankshaft.
Re: Simple, solar-powered water desalination
#195Earlier quoted context omitted.
You can make a solar still without desiccants. Dig a hole somewhere that will get sunlight most of the time, drop a cup in the bottom to catch water, and create a funnel with a plastic sheet. (If you don't have a plastic sheet, branches can work.) There are various ways to optimize it, but a single water trap isn't going to keep a person alive.
But if they're cheap and easy, and a person could make a dozen, that changes things a bit. But still, I think we're still talking about short term survival only. If that's your environment, the local flora & fauna are unlikely to be prolific enough to fill other needs without extensive effort. Unless, you know, you've got a Still suit and can call giant worms and stuff.
The thing is- this could work without intervention - and without the intention of keeping humans alive for years, thus creating a ecosystem over time. Somewhere in the middle of nowhere- watering cacti, then hardened other plants, reclaiming the moisture they loose, until bushes and trees take over these functions.
Its hard describing this fascination with self-contained or only slowly expanding pockets of life.. imagine a glass bubble , filled with small plants, beatles and life, thriving in the midst of a frozzen over wasteland like mars or a dessert like the death valley.
Its like a https://en.wikipedia.org/wiki/Bottle_garden but without the surrounding walls..
Re: Simple, solar-powered water desalination
#196Efficiency in desalination is measured by comparing the energy expenditure to the enthalpy of vaporization of water (basically the energy required to distill water by boiling it). The current state of the art reverse osmosis desalination plants use about 3.2 KWh of electricity per cubic meter of fresh water ( https://pdfs.semanticscholar.org/d4d7/821d585699719289dddd10... ). This technology uses about 173 KWh of sola…
You actually don't even really need the batteries. Israeli utility scale desal is designed to operate in variable mode, in their case they run about 10% capacity during summer days and 100% during summer nights. Their grid peaks are air conditioning dominated which is why that pattern.
It does mean much larger service water tanks as you need to buffer demand but if you have lots of "free" solar power then it may well be worth it.
Re: Simple, solar-powered water desalination
#197Earlier quoted context omitted.
I found this video which seems to animate the concept nicely: https://www.youtube.com/watch?v=udffed4Pq3g
Bloody Hell I did not know that. I have parts of broken Katadyn PUR-06. I was thinking of rebuilding it from better materials. The pressure recovery is the worst part. I can totally fathom now a hand-held desalinator with only rotating parts running from solar or Li-On batteries.
I don't know how well this would scale down. Viscosity would work against you.
Re: Simple, solar-powered water desalination
#198This is not only about efficiency. As noted in the article, it would reduce the pollution of highly concentrated brine rejected into the ocean. See for instance this article of the Guardian about a region in Chile where the majority of drinkable water comes from a desalination plant built in 2003: "The salt they pump back in kills everything'" https://www.theguardian.com/cities/2020/jan/02/the-salt-they...
It only does that by virtue of being much less efficient and spread over a larger area than traditional desalination plants. At the end of the day unless you're storing that brine or trucking it off somewhere you have to dump it back in the ocean. That "highly concentrated brine" isn't all that concentrated to begin with as it's less than a 50% increase in solutes coming out of the discharge pipe and gets mixed and diluted in the ocean relatively quickly. That article is just a fisherman blaming an unrelated problem on the closest thing around.
Re: Simple, solar-powered water desalination
#199Earlier quoted context omitted.
But the processing and shipping isn’t the problem with desalination. The problem is that dumping bribe or salt into the ocean can kill local wildlife.
They dump the salt outside the environment. https://www.youtube.com/watch?v=3m5qxZm_JqM Seriously though, far out to sea away from any landmass it's pretty much a desert. Any salt dumped there would disperse very quickly and not pose a problem to wildlife.
Since the brine is denser than water, a long hose could deliver it to the ocean bottom for just the cost of the hose. There are lakes of dense brine on the sea floor already.
Almost every part of the world ocean has been described as a desert, before people went under and looked. It turns out there's a huge amount of life everywhere you look, even miles down.
But there is also a lot of room, so anything localized, unpleasant, and temporary can be swum away from.
Re: Simple, solar-powered water desalination
#200Earlier quoted context omitted.
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.
Describing the Hudson as drinkable is somewhat ahistorical: https://en.wikipedia.org/wiki/Pollution_of_the_Hudson_River In any event, NYC gets its water from upstate, not locally: https://en.wikipedia.org/wiki/New_York_City_water_supply_sys...
Still, compared to space needed for desalination, it's not obvious that the current scheme uses less area (I do assume you can still do some things, like hiking, in most of this area though) :
"One of its largest watershed protection programs is the Land Acquisition Program, under which the New York City Department of Environmental Protection (DEP) has purchased or protected, through conservation easement, over 130,000 acres (53,000 ha) since 1997"