[HN Gopher] From seawater to drinking water, with the push of a ...
___________________________________________________________________
From seawater to drinking water, with the push of a button
Author : happy-go-lucky
Score : 235 points
Date : 2022-04-29 02:43 UTC (20 hours ago)
(HTM) web link (news.mit.edu)
(TXT) w3m dump (news.mit.edu)
| Simon_O_Rourke wrote:
| If this works the way it looks like it does, these devices will
| be a literal life saver. Would love to see a buy-one-donate-one
| purchase plan.
| nkingsy wrote:
| From the article:
|
| The limitations appear to be expensive materials and scale.
|
| 20w per liter .3 liters per hour
| moffkalast wrote:
| > expensive materials and scale
|
| Aka, we'll never hear about this ever again.
| MichaelApproved wrote:
| The article claims 3x more efficiency in a confusing sentence:
|
| _"Their prototype generates drinking water at a rate of 0.3
| liters per hour, and requires only 20 watts of power per
| liter."_
|
| So the unit only produces 0.3 liters an hour but if you wait 3
| hours and provide 20 watts of power (7watts/hour), you'll have
| a full liter.
| qayxc wrote:
| > So the unit only produces 0.3 liters an hour but if you
| wait 3 hours and provide 20 watts of power (7watts/hour),
| you'll have a full liter.
|
| That doesn't make any sense. 20W of power draw over 3 1/3
| hours is [?]67Wh (Watthours, not Watts per hour), so 67Wh per
| litre (energy use; independent of time) and it takes 3 1/3
| hours to get this litre of potable water with 20W of power.
|
| In other words to get 1 litre in an hour, the device _might_
| require [?]67W of power (assuming that kind of perfect
| scaling is even possible with their design).
| BeefWellington wrote:
| The wording in the article is specifically:
|
| > requires only 20 watts of power per liter.
|
| Whether the article is accurate or not I think you missed
| that.
| qayxc wrote:
| The point is that 7W/hour is nonsensical. It's a non-unit
| and physically doesn't make sense in any context. The
| power is independent from the volume. Total energy use is
| volume dependent.
|
| 20 Watts per litre is mix of units that's nonsensical.
| Watt is Joules (Energy) per second (time), i.e. power.
| Either time is irrelevant, that is the device draws 20
| Watts of power, in which case you can ditch the litre. Or
| the power draw is dependent on the performance in that
| more power equals higher throughput.
|
| Neither case is in any way shape or form correctly
| described by "20 Watts per litre". Hope that makes it
| clearer now.
| BeefWellington wrote:
| Science reporting is not great but colloquially people
| use 20W per <job done> as a way of meaning Watt-hours.
|
| If this is correct, they're saying it takes 20 watts
| (meaning Wh) to deliver a Litre of water, over three and
| a bit hours. The time _is_ provided just obfuscated by
| their "we deliver 0.3L/hour" statement, so by saying
| 20W/L it does sort of make sense within the context.
|
| ~6W/hour (if it means we use a total of 6Wh) would be
| different than claiming the system runs off 0.1 Watts.
| Given the size of that solar panel, I suspect they're
| claiming they are using ~6 Watts for a period of one hour
| to produce 0.3L. Alternately, they're just flat out wrong
| and they're using 20 watts for one hour to produce 0.3L.
|
| It could be worded better but I think this is what
| they're trying to say is that they're consuming 6W.
| qayxc wrote:
| > Science reporting is not great but colloquially people
| use 20W per <job done> as a way of meaning Watt-hours.
|
| After watching the video I can confirm that it's actually
| 20Wh/l for 0.3l/h and 15Wh/l at 1l/h (I'm a bit puzzled
| how that works, but hey - that's what the inventor says).
|
| > It could be worded better but I think this is what
| they're trying to say is that they're consuming 6W.
|
| I would be happy if they'd manage to simply repeat what
| was said in the video. This is the official MIT news
| portal after all and I would expect it to be run by
| people smart enough to use the correct units, but alas...
| yellow_lead wrote:
| Anyone else notice in the beach video that the researcher filled
| the cup using tubing that was previously on the ground, then
| drank it? Looks cool though :)
| netsharc wrote:
| He did wipe the sand off the output tubing... good enough?
|
| I guess if I dropped a drinking straw on the ground in an e.g.
| parking lot, I'd throw it away, but if I dropped it on sand in
| the beach, I would think "just wipe the sand off and it's
| clean!"
| xtracto wrote:
| Back in the day when I went camping with my parents we used
| to "wash the dishes" using seawater and sand from the beach.
| Nowadays people are unnecessarily germophobic.
| mothsonasloth wrote:
| What about filtering particles which don't have a charge like
| plastics or biological matter?
|
| I guess you can always just boil the water after it's been
| processed by the portable machine.
| eps wrote:
| I didn't quite get this part either -
|
| > _The membranes repel positively or negatively charged
| particles -- including salt molecules,_ bacteria, and viruses
| ...
|
| Are bacteria and viruses indeed electrically charged? This
| sounds strange.
| beanjuice wrote:
| Yes [0], "Bacterial cell surfaces possess net negative
| electrostatic charge by virtue of ionized phosphoryl and
| carboxylate substituents on outer cell envelope
| macromolecules which are exposed to the extracellular
| environment."
|
| [0] https://doi.org/10.1016/S0167-7012(00)00224-4
| timonoko wrote:
| Those specifications are _much_ worse than 30 year old PUR-06. It
| makes one liter per hour with 20 Watts and fits in your pocket.
|
| I tried solar panel and windshield wiper motor. But direct-drive
| windmill was much better as wind blows 24/7 on Baja.
| https://youtu.be/9xYXWISWv5I?t=390
|
| Durability was the issue. I destroyed three units and average was
| 200 days / 1000 liters, because all-plastic construction. Found
| no limits on filter durability.
| timonoko wrote:
| I was planning to make those crucial breaking parts from Carbon
| Fiber myself, but I was such a poster-boy for PUR that they
| sended me free PUR-35 ($5000). It makes 3 liters per hour and
| if you replace the solid-iron pumping shaft it weighs about a
| kilo.
|
| Except one crucial high-pressure valve cannot be made of
| plastic. I made better one from fiber glass. Thereafter it been
| running ok for 20 years.
| gonzo41 wrote:
| This is a pretty cool development, even if they made this thing
| the size of a 20ft shipping container it'd be a pretty good
| development.
| zubairq wrote:
| Amazing! Is this a game changer?
| qayxc wrote:
| Probably not. It's more expensive than available alternatives
| (according to the article they use expensive materials) and the
| performance is poor compared to commercially available
| alternatives.
|
| Might be useful for certain niche applications, but outside of
| that it's more of a proof of concept at this point.
| siruva07 wrote:
| Maybe. I think Atmospheric Water Generators are much More
| likely to change the game since they don't need a body of water
| other than the atmosphere.
| stephen_g wrote:
| There are big thermodynamic problems with those, the phase
| transition requires a lot of energy... Generally the main
| places where they work with any kind of acceptable
| efficiently and decent yield (where there's high enough
| humidity) are also the places where it tends to rain a lot!
| MichaelApproved wrote:
| " _Atmospheric Water Generators_ "
|
| At first I thought you were just using a marketing term for
| dehumidifiers but I looked it up before posting.
|
| I see that term is used for tight mesh fabric that's hung
| vertically as a passive matrix to collect condensation.
|
| While those are actually game changers, they unfortunately
| only work in special regions that have the needed weather and
| topography to make them work.
|
| I think there's only one place on earth that has the perfect
| combination for AWG: weather, drought, and humidity. It's an
| awesome technology for them but that's about the extent of
| it.
|
| I'll try to find the region and update my comment with more
| info.
|
| Edit: here's a video that talks about what I think you're
| talking about.
|
| https://youtu.be/YxRONAZoMDk
|
| It's providing water in the Atacama Desert near Lima Peru.
|
| Edit 2: They're called fog collectors and apparently Morocco
| uses them too. https://youtu.be/0F7CQMd6mQ4
| FR10 wrote:
| > It's providing water in the Atacama Desert near Lima
| Peru.
|
| I think one big issue is that in winter (May-September) not
| every day is foggy, so sure its helpful but not a perfect
| solution. It does get really foggy though in June-October.
| Thus we get natural vegetation in otherwise arid hills
| around Lima, the most popular called Lomas de Lachay[0].
|
| [0] https://en.wikipedia.org/wiki/Lachay_National_Reserve
| fiddlerwoaroof wrote:
| I wonder if you could use a similar sort of device with
| weather balloons to harvest water from clouds.
| kortex wrote:
| I could totally see a Project Loon style craft which
| automatically surfs the crosswinds, going up above the
| clouds to radiate heat to the open sky at night, and
| descending to condense water.
| MichaelApproved wrote:
| Would dry regions that need water have enough cloud
| coverage for that to be viable?
|
| My guess is that any place with sufficient cloud coverage
| is already getting enough rain water to satisfy their
| needs.
| fiddlerwoaroof wrote:
| I think there are parts of coastal California where there
| are clouds more of the year than rainfall. I'd also
| suspect if you just raised them up with balloons to cool
| them off and then brought them down where it's warmer,
| you could condense evaporation from the ocean, without
| spending energy directly on cooling.
| MichaelApproved wrote:
| You'd have to raise them up pretty high to get them
| colder than the dew point.
|
| The energy it'd take to raise and lower the material
| would make it cost prohibitive.
|
| I considered that the balloons would be a balancing force
| but don't forget the rope length changes as the balloons
| go up and down. That changing length shifts the weight
| around. You can't be balance against it.
| ratsforhorses wrote:
| Atmospheric water generation (AWG) uses technology to
| produce potable water from surrounding air.
|
| Here's a cool example of using the sun to do just that...
|
| https://youtu.be/VQRAtwz3Igs
|
| https://en.m.wikipedia.org/wiki/Atmospheric_water_generator
| [deleted]
| denton-scratch wrote:
| > requires only 20 watts of power per liter.
|
| So if you want a liter, you have to supply 20 watts. For how
| long? Forever? Does the water instantly become turbid when power
| is removed?
|
| Tsk, tsk, MIT. I would have thought an MIT journo would know what
| a watt is.
| aaron695 wrote:
| davelondon wrote:
| When someone uses watts as a unit of energy, they mean watt
| hours. It's very common.
| davelondon wrote:
| ... and in the video they specify 20Wh/L.
| soVeryTired wrote:
| > Their prototype generates drinking water at a rate of 0.3
| liters per hour, and requires only 20 watts of power per liter.
|
| Not great phrasing I agree but the information is there.
| qayxc wrote:
| Nah, still doesn't make any sense either way.
|
| Watts is a measure of power, not energy. The amount of power
| (given they use a pump and electrodialysis) shouldn't depend
| on the volume. Energy OTOH does.
|
| So either their device requires 20W of power - which sounds
| reasonable as the image shows a <100Wp solar panel next to it
| - and the volume figure is meaningless.
|
| Or the author left out crucial context (e.g. is the power
| draw correlated with the speed, i.e. 20W @ 0.3l/h).
|
| The amount of energy would be 67Wh/l regardless given those
| numbers. It's just a confused mix of performance (processed
| volume per hour) and power requirements (which is independent
| of volume and should only depend on the performance).
| denton-scratch wrote:
| The trailing "per liter" seems the problem: I think maybe
| what they mean is that 20W gets you 0.3 liters per hour? So
| their machine produces 0.3 liters per hour, and draws 20W?
|
| I wish journos wouldn't bandy around terminology and
| statistics they don't understand. It's getting worse.
| SamBam wrote:
| It isn't, though, because that would be 60Wh per liter, but
| the video actually specifies it's 20Wh per liter.
|
| They just stupidly used watt instead of Wh in the article
| text.
| nullc wrote:
| So how is this distinguished from existing commercially available
| continuous electrodeionization?
| qayxc wrote:
| Uses less power and is portable? That's pretty much all I could
| gather from the article.
| nullc wrote:
| That's its claimed advantages against reverse osmosis.
| kylehotchkiss wrote:
| Southern California is beginning to see more water restrictions -
| each and every desalination tech advancement is a very hopeful
| development for the region, and many others in the world that
| can't get enough freshwater. I hope they can generally work this
| up to factory scale and put it behind a solar farm and see if
| that can supply a lot of homes.
| KennyBlanken wrote:
| The problem is that southern California is trying to grow a
| shit-ton of crops that aren't suitable for the environment
| there. The almond industry is particularly guilty in this
| regard.
|
| Desalination will never scale to a level suitable to supply
| that industry. If anything they'll take that water and just
| grow even more crops, while still sucking the aquifer dry.
|
| Thing is, aquifers compact when you draw water from them too
| much. That compaction can never be undone. They are slowly
| rendering that land permanently uninhabitable.
| qayxc wrote:
| > Desalination will never scale to a level suitable to supply
| that industry.
|
| Are you sure about that? It's simply a question of economics.
| As long fresh water from other sources is significantly
| cheaper, no one's going to invest in large scale
| desalination.
|
| Once this changes it becomes a question of which is more
| expensive - shutting down the agribusiness or running large
| scale desalination (which has options, from nuclear to solar
| to the use of metamaterials).
| sp332 wrote:
| It is true in California, because you need to dump the
| concentrated brine somewhere, and doing that at industrial
| scale will run up against environmental protections.
| jillesvangurp wrote:
| There's a big bucket right next to California called the
| Pacific. Perfect place for sourcing water to desalinate
| and dumping brine back into without doing anything
| measurably harmful to salt concentrations in the Pacific.
| It's like a literal drop in the ocean. Most big
| Californian metropolitan areas are right next to it.
| There is no water shortage; just a reluctance to pay a
| fair price for it.
|
| The challenges in California are not technological but
| political and policy related. Local consumers of water
| seem to assume that water is like manna from heaven that
| has to be perpetually subsidized by the government. They
| feel entitled to it but are not really willing to pay for
| it; or even invest in common sense ways to reduce their
| consumption of it because it doesn't really cost them
| anything.
| KennyBlanken wrote:
| If I had a dollar for every project MIT's press office has said
| will be revolutionary and end (insert major world
| health/water/resource/energy/food problem), I'd be a very, very
| rich person.
|
| I'm not sure why MIT's press office gets so much favor here,
| particularly given their/MIT's track record.
|
| Post articles by science journals and news outlets that will tell
| us if this is actually going to work or if it's just yet another
| go-nowhere project.
| swader999 wrote:
| At least this instance has a workable demonstration. Looking at
| you battery tech...
| JoeAltmaier wrote:
| With advances, perhaps one day it will be the size of a pack of
| cigarettes. And thus portable enough to include in an emergency
| kit!
| smiley1437 wrote:
| Am I reading this wrong? It uses less energy at higher production
| rates?
|
| This is a verbatim copy of the text at 1:32 in their video:
|
| Seawater >> Drinking Water
|
| ~ 20Wh/L for 0.3L/h of production rate
|
| ~ 15Wh/L for 1.0L/h of production rate
|
| so it uses LESS energy to get MORE drinkable water per hour?
|
| That seems odd.
| SamBam wrote:
| They show that the 1L/h version uses more elements.
|
| I assume there are some efficiencies as you get larger.
| davelondon wrote:
| I assume this means with a larger device...
| smiley1437 wrote:
| Okay that makes sense
| sandworm101 wrote:
| >> The researchers also created a smartphone app that can control
| the unit wirelessly and report real-time data on power
| consumption and water salinity.
|
| No no no no. I was all onboard with this seemingly wonderful
| product until I hit that line. The things that provide fresh
| water, that actually enable life functions, should NEVER involve
| controller aps. Switches. Dials. Positive on/off switches. Maybe
| the occasional touchscreen. But please do not put the need for a
| working/charged/connected cellphone between the user and their
| source of fresh water.
|
| And they say that this thing uses about as much power as a
| cellphone charger. Wrong. It requires the power of a cellphone
| charger to filter water, plus a _second charger_ to power the
| cellphone running the app.
| joshuaheard wrote:
| A cell phone app would be handy for remote monitoring and
| control. Say you lived a mile away from the ocean where it is
| deployed. You could turn it on and off depending on the tide
| and know when the container you are filling is full.
|
| Having just completed a home remodel where all the home
| automation features have an app, having apps is a handy way to
| monitor and control your hardware without leaving your couch,
| or even if you are off-premises.
| sandworm101 wrote:
| But does the pipe bringing fresh water into your house use an
| ap? There are things in this life that are expected to "just
| work", that are so basic they should not be trusted to aps.
| This product isn't for a fancy house in a city. It is a
| portable product meant for use in remote areas, by soldiers
| no less, far away from working cellphone towers or reliable
| power supplies. Serious consideration should be given before
| attaching anything more complicated than an on/off toggle
| switch.
| xtracto wrote:
| Right, the more I learned about computers and automation,
| the more I want dumber stuff. Intelligent doorlock? Alexa
| lights? Ring? Nooo thank you, I don't want to be left out
| of my home or without light because of some internet error.
|
| I like my electronics like my dogs: dumb as a mule.
| tzot wrote:
| >> The researchers also created a smartphone app that can
| control the unit wirelessly and report real-time data on power
| consumption and water salinity.
|
| > No no no no. I was all onboard with this seemingly wonderful
| product until I hit that line. The things that provide fresh
| water, that actually enable life functions, should NEVER
| involve controller aps. Switches. Dials. Positive on/off
| switches. Maybe the occasional touchscreen. But please do not
| put the need for a working/charged/connected cellphone between
| the user and their source of fresh water.
|
| You are objecting to a strawman of your own creation. Before
| you hit that line, you read "The technology is packaged into a
| user-friendly device that runs with the push of one button."
| and "The researchers designed the device for nonexperts, with
| just one button to launch the automatic desalination and
| purification process."
|
| And then comes the line that triggered your reaction: "The
| researchers also created a smartphone app that can control the
| unit wirelessly and report real-time data on power consumption
| and water salinity."
|
| The key word is "can". "Can control", "can report".
|
| So you have the simplest possible device: press a button on the
| device, extract drinkable water. You want status updates /
| remote control? Use the app, which is optional; nowhere in the
| article it is stated that the app is necessary.
|
| So you might reconsider your stance and get back onboard with
| the product.
| dehrmann wrote:
| > The suitcase-sized device...can also be driven by a small,
| portable solar panel,
|
| > Yoon and Kang used machine learning to find the ideal
| combination of ICP and electrodialysis modules.
|
| These bits feel like they were added because ML and solar power
| will get more clicks.
| SturgeonsLaw wrote:
| True, especially using ML to determine the size/layout of the
| components. That could be very easy assessed by varying the
| sizes in a consistent, linear way, and measuring the
| effectiveness in subsequent tests, rather than throwing it into
| the black box of ML.
| SamBam wrote:
| ML maybe, but solar power definitely not. They show an example
| use-case as a single-family house in a site of flooding and
| devestation. An emergency desalinator would definitely need to
| run off of a small generator or solar.
| eps wrote:
| > _The research was funded ... the Experimental AI Postdoc
| Fellowship Program of Northeastern University, and the Roux AI
| Institute_
|
| That's the cause of the AI part.
|
| The solar panel bit probably came from the Army requirements,
| who's another sponsor.
| davelondon wrote:
| Not sure this is better than reverse osmosis... They mention
| ~15Wh/L @ 1L/hr... The Katadyn Powersurvivor 40 (pretty compact
| and 11kg) uses 8.5Wh/L @ 6L/hr...
|
| https://www.spectrawatermakers.com/us/us/89650-8013438-Katad...
| sp332 wrote:
| Once an RO filter gets clogged, it stops working.
| MichaelApproved wrote:
| Edit: I wrote out the comment below criticizing the efficiency of
| this device, when compared to reverse osmosis RO desalination
| (100x less efficient).
|
| However, they're not trying to be more efficient than RO devices,
| they're trying to be more compact, portable, and avoid the need
| for filters.
|
| They're solving for a different problem than I was measuring them
| against.
|
| In my race to criticize, I overlooked those key details.
|
| I still think my comment is worth reading to learn about the
| efficiency differences but I guess that measurement is not
| important for the viability of this technology.
|
| Original criticism below: --------------
|
| I'm skeptical about how practical this actually is.
|
| While it's refreshing to see a drinking water solution that isn't
| based on inefficient dehumidifier technology, this still seems
| impractical.
|
| From the demonstration video, their portable ~50 watt solar panel
| took 30 minutes to get a few ounces of drinking water.
|
| It looked like a cold winter day, so let's be generous and assume
| the panel only produced 15 watts of power during those 30
| minutes.
|
| Let's also be generous and say they got 5 ounces of water.
|
| That means they produce 1 ounce of water for every 3 watts.
|
| That'd be 333 ounces per kWh.
|
| To put that into perspective, a desalination plant produces more
| than 100x that much.
|
| Yes, there is lots of additional infrastructure to consider with
| a traditional desalination plant but It's not like this solution
| wouldn't require the same complexity to scale up.
|
| I don't remember the cost of dehumidifier drinking water
| "solutions" but I think this is _slightly_ more efficient than
| those horrifically inefficient solutions.
| scoopertrooper wrote:
| The article says they can get 1 liter for every 20 watts. So
| that'd give them 17,597 ounces per kWh.
| denton-scratch wrote:
| It does say that; and you've converted between watts and
| watt-hours. The article's claim doesn't make sense.
| SamBam wrote:
| I feel like nobody watched the video (although I do wish
| the article text had been clearer).
|
| The video specifically shows (at 1:34) that the machine
| operates at 15Wh/L (for the larger version, the smaller
| version is 20Wh/L).
|
| This is 15Wh/33 oz (since we seem so set on using customary
| units), or 2200 oz per kWh.
| denton-scratch wrote:
| I didn't; I don't generally follow video links, unless I
| deliberately went looking for a video. Specifically, I
| don't follow many video links from HN; I treat HN as a
| text/plain site.
|
| So my remarks were only about the article text.
| [deleted]
| SamBam wrote:
| The video claims that the machine operates at 15Wh/L (for the
| larger version, the smaller version is 20Wh/L).
|
| This is 15Wh/33 oz, or 2200 oz per kWh.
|
| That's roughly one order of magnitude greater than your
| estimate.
| dfsdf4sds wrote:
| I want to thank you for your edit, and for keeping the original
| text. Recognizing something you said ignored portions of the
| argument, changing the argument, and keeping the original
| portion to show _why_ you were wrong but still adds to the
| conversation is very valuable. I commend you for your ability
| to double guess yourself
| MichaelApproved wrote:
| Thank you. And you're right, I am amazing ;)
|
| But seriously the main reason I write these comments is to
| work through my thoughts as I try to articulate them and get
| feedback on what I'm thinking.
|
| I'm actually happy when someone points out a mistake because
| I learned something.
|
| When I'm right, I haven't gained anything. Sure, my ego
| enjoys the satisfaction of being right but my already
| inflated ego doesn't need anymore stroking.
| Damogran6 wrote:
| My biggest issue is when I hit send on something when what
| it really needed was another editorial revision.
| MichaelApproved wrote:
| I almost instantly hit the edit button after I post a
| comment.
| bombcar wrote:
| Heh sounds like what Socrates said - it's better to be
| corrected than to be correct.
| antisthenes wrote:
| It's even better to be correct after being corrected by
| yourself.
| tomxor wrote:
| From the article it sounds like they are looking for ways to
| scale down (i.e small portable units _are_ the target form
| factor, not a mere demo), and this is where it compares
| favourably against things like reverse osmosis for efficiency.
| MichaelApproved wrote:
| I was so quick to criticize technology that I completely
| overlooked those points. Reading the article again, it's
| embarrassing to see that I missed it when they were
| emphasizing it so much.
|
| I have one more lingering criticism that I don't think they
| addressed (I reread it twice).
|
| What happens to the salt after it's removed? If they don't
| have a filter, where does it go? Do they pump brine water
| back?
| QuikAccount wrote:
| You can pump brine water back but if I recall you can't
| just dump it all back at once because it's so highly
| concentrated. Ideally you would be able to find an
| alternate use for it.
| MichaelApproved wrote:
| For these small amounts, I doubt pumping it back out
| would be an issue but is that what they're doing?
|
| I thought the metal plates were collecting the salt but
| the article and video don't make it clear.
| nullc wrote:
| In CEDI at least the ions are trapped in a resin then are
| driven across a membrane by a charge, on the other side
| of the membrane you run water to flush them out.
|
| Some comment in the article left me thinking they end up
| trapping them in the media and have to reverse charge to
| release them so I assume it would operate pulsed and
| presumably have a valve to dump the output during regen.
|
| Though I'm a little confused in that normally CEDI is
| used after RO because the CEDI media is pretty sensitive
| to fouling and also doesn't work well when the water
| conductivity is highly variable. Maybe they solve the
| fouling with charge reversal.
|
| ...who knows, because popular coverage of this stuff
| never hits on the important parts and almost never links
| the relevant publications. There are many ways to make
| drinkable water from seawater-- making them some useful
| mixture of energy efficient, cost effective, portable,
| waste-water efficient, and reliable is the actual hard
| part.
| bruce511 wrote:
| given the size of the thing it's likely to be positioned
| very close to the water source, so I expect it just dumps
| it outside the device. I mean, if I was running it on a
| boat, or next to the sea, I'd just basically pour the
| waste out right next to the device.
|
| And I agree, at ounces per hour there's no need to dilute
| the brine, just dumping it is fine.
| tomxor wrote:
| Note that they are not merely aiming for portability, but
| efficient portability.
|
| This particular passage is suggestive of their device being
| more efficient than RO at small scales, although no figures
| are given for comparison:
|
| > Commercially available portable desalination units
| typically require high-pressure pumps to push water through
| filters, which are very difficult to miniaturize without
| compromising the energy-efficiency of the device, explains
| Yoon.
| MichaelApproved wrote:
| Good point. I wish articles like these would include
| figures. I'd love to know what they calculate RO
| efficiency to be at small scales and how far away they
| are from beating it.
|
| Sure, that might be boring for some readers but they
| could throw a couple of sentences about it at the bottom.
| electroly wrote:
| FWIW, I think you made a minor math error; you lost track of
| the 30 minutes. It would be 1 ounce of water for 3 watts of
| power _over 30 minutes_ , which is 1.5 Wh of energy. That's 666
| ounces per kWh.
| pnutjam wrote:
| Whelp... you just killed this tech by linking it to the
| Devil's number. hope you're happy. /s
| MichaelApproved wrote:
| It wouldn't be the first time I made a mistake like that by
| not clearly identifying my units but I think I got it right.
|
| Let me rephrase and use watt/hour units.
|
| I was assuming it was a 50 watt panel that would only produce
| 30wh from the weak winter sunlight.
|
| Divide 30wh by two (since it was only ru Ning for half an
| hour) and get 15 watts generated to purify 5 ounces.
|
| Had they let it run for the full hour, they'd get 10 ounces
| from my assumed 30wh of energy the panel produced.
|
| 30wh divided by 10 ounces would be 3wh per ounce (or unit of
| water produced).
|
| How many units of water can be produced by 1kwh? Let's divide
| 1,000wh by 3wh to get the result of 333.3 units (ounces)
| produced.
| electroly wrote:
| Wh is a measurement of energy, but W is a measurement of
| power (that is, the rate of energy). They are different
| units of measurement and you're mixing them up here. Here,
| you've doubled the original rating of 15 watts up to 30
| watts; that's the result of the confusion between energy
| and power. You don't divide the wattage in half when you
| run it for half the time, nor double it when you run it for
| twice the time; that's not how power works. That's how
| _energy_ works.
|
| In your original post, the number was 15 watts, and you
| figured it produced 5 ounces of water in 30 minutes. So you
| then figured that 3 watts can produce 1 ounce of water in
| 30 minutes. So far so good; that's correct. If the panel
| continuously produces 3 watts of power (remember: watts are
| a _rate_ of energy) over a period of one hour, that 's 3
| watt-hours of energy. For 30 minutes, it's 1.5 watt-hours
| of energy. Thus, it took 1.5 watt-hours of energy to
| produce 1 ounce of water. (1000 watt-hours) * (1 ounce /
| 1.5 watt-hours) = 666 ounces.
|
| It may make more sense to translate this into distance,
| which I think is more intuitive for most people. Watts
| (power) are like miles-per-hour (velocity), and watt-hours
| (energy) are like miles (position). The panel runs at 15
| MPH. After 30 minutes it has run 7.5 miles and produced 5
| ounces of water. Thus, it could produce 1 ounce of water by
| running just 1.5 miles. It still runs at a speed of 15 MPH
| no matter what.
| zmgsabst wrote:
| You're getting confused by their typo on units:
|
| They meant 15 watt-hours in both cases, which would be
| half of 30 watt-hours -- or a 50 watt panel for 30
| minutes at 60% efficiency. (Which is the stated working
| premise.)
|
| 15 watt-hours -> 5oz would imply that 3 watt-hours ->
| 1oz, and hence 1 kWh is 333oz.
|
| I generally try to assume best intentions -- so if they
| repeated otherwise the same correct math, but for
| misnaming a unit, I try to assume they're correct and
| typo'd.
| MichaelApproved wrote:
| OP here. Thanks for understanding what I'm trying to say
| and putting it in the correct terminology.
|
| However, I think I'd still make the same mistake in the
| future because I don't understand how to express what the
| (assumed) 50 watt rated panel is generating over half an
| hour.
|
| If it's running at 60% efficiency then it's generating at
| 30 watts per hour.
|
| After an hour of running, we've accumulated 30 watts of
| energy.
|
| If we only ran it for half hour, we'd have 15 watts.
|
| Dividing that out tells me that 3 watts of energy will
| provide 1 once of water.
|
| Does it matter if those 3 watts are provided over an hour
| via a 3wh power source or over 10 minutes via a 16wh
| power source?
| zmgsabst wrote:
| This is what the other person was trying to say:
|
| "Watt" is the unit of _power_ which is the rate of change
| in "joules", which is the unit of _energy_. In the way
| that "velocity" is the rate of change in "position".
|
| 1w = 1J/s
|
| A "watt-hour" is another way to represent joules/energy
| by integrating watts/power over time.
|
| 30 watts * 30 minutes = 15 watt- _hours_ or 54 kJ.
|
| 30 miles/hour * 30 minutes = 15 miles or 24km
|
| > Does it matter if those 3 watts are provided over an
| hour via a 3wh power source or over 10 minutes via a 16wh
| power source?
|
| You have the units backwards:
|
| You can get 3wh from 1 hr @ 3w or 10 min @ 18w.
| MichaelApproved wrote:
| Thanks. I'll need to read that a few times because I
| struggle with this constantly.
| zmgsabst wrote:
| I think part of the confusion is we don't normally have
| units for rates of change.
|
| So let's create one: the "walk" is the speed a person can
| walk -- 3mph.
|
| Then I can say the store is "3 walk-hours away", even if
| I normally drive the 9 miles with my car.
|
| 3 walk-hours = 3 hours @ 1 walk = 18 minutes @ 10 walk
| (or 30mph)
|
| Batteries are rated in "watt-hours" for the same reason:
|
| 3wH = 3 hours @ 1 watt = 18 minutes @ 10 watt
| yyyk wrote:
| I recall similar in function devices already existed for military
| use - except they made water from air, which is even more
| available than seawater:
|
| https://www.honeywell.com/us/en/press/2021/05/honeywell-led-...
|
| https://edition.cnn.com/2014/04/24/tech/innovation/machine-m...
| aemreunal wrote:
| Fun fact, there's vodka made from San Francisco fog:
| https://time.com/4317269/fog-vodka-san-francisco-hangar-one/
| photochemsyn wrote:
| If this unit is shown to be durable, I imagine it's the kind of
| thing a lifeboat would have as part of its equipment. Low power
| means low volume of drinkable water (as energy is needed to
| separate ions from seawater, by the laws of entropy), so that's
| really unavoidable with this system.
|
| Compare to things like concentrated solar for complete removal of
| solids from wastewater and seawater, here's an interesting
| example (relies on condensation of steam):
|
| https://influencing.com/pr/99083/novel-solar-powered-water-t...
| Stevvo wrote:
| This thing is going to cost more and be far less capable than a
| traditional suitcase or even hand-pump desalinator and you
| never see those on lifeboats.
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