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Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

utexas.edu

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Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#31

Post by stephengillie »

dangrossman wrote: post #13
stephengillie wrote: post #7

Earlier quoted context omitted.

A solar panel can run this. Or, to be more specific, a small (3" x 3") solar panel could charge a 3v battery which could power this device. I have solar-powered holiday lights which operate on 3v, this application would be simply replacing the lights with this chip. I've actually replaced the charging circuit with a TI MSP-430[1], and powered it directly with solar power. [1]a microcontroller similar to Arduino which…

This thing is producing nanoliters per minute with that power. Sure, you can power this device with a small panel, but you'll die of thirst before it makes enough water to fill one glass.

Hopefully they optimize the device for v0.2 ;)

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#33

Post by rflrob »

haldujai wrote: post #21

Original paper: doi: 10.1002/anie.201302577 From their paper it is mentioned they have a 40 nanolitre/min flow rate (25% desalination rate, 99% is considered safe to drink water). They use an electric pole to generate an ion depletion zone, their problem right now lies in the severely limited flow rate and desalination rate. From my understanding the 25% desalination rate does not compound linearly and decreases in e…

>Additionally their flow rate is 0.4 microlitres per minute, this would equate to needing 625 000 channels for one pass only to get 250mL / min. Scaling for microfluidics isn't simply using a larger pipe size, microfluidic devices largely operate with minimal forces and a Reynolds number of 1, that doesn't hold as you get larger.

What about parallelization? Are there any obvious downsides to simply having lots of the active units, aside from the (what seems to me largely manageable) increase in micro fluidic chip complexity?

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#34

Post by sbierwagen »

jonmrodriguez wrote: post #30
HCIdivision17 wrote: post #27

Earlier quoted context omitted.

I had an electrical engineering old timer explain the misconception as the Current Push Theory. (His industrial war stories were pretty good.)

Googling for "Current Push Theory" only gets 5 results, none of them relevant: https://www.google.com/search?num=100&q=%22Current+Push+Theo... Can you please define the Current Push Theory?

He might be referring to the "hydraulic analogy" of electricity: A wire is a water pipe, voltage is water pressure, amperage is total water flow. A battery is a pump pushing water through the pipes, voltage is how hard the pump pushes, and amperage is limited by how wide the pipes are, and thus how much resistance they impose on the flow of water.

http://en.wikipedia.org/wiki/Hydraulic_analogy

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/watcir.h...

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#35

Post by ScottBurson »

sbierwagen wrote: post #16
solox3 wrote: post #15

Earlier quoted context omitted.

0.7A is the current of the "store bought" (AA) battery, suggested by the article. To make this technology energetically favourable to boiling, it must not exceed ~700μA in current, and it has to be far less than that to be worth its complexity.

Uh? No battery[1] delivers a constant amount of current: http://en.wikipedia.org/wiki/Ohm%27s_law Solving for current, Ohm's law is I = V/R. You only deliver .7 amps of current into a 4.285 ohm load. If you connect a 3 volt battery to a 1,000 ohm resistor, then only 0.003 amps of current will flow, which is 9 milliwatts. Connect a 3 volt battery to a .01 ohm load (a dead short, almost) and 300 amps of current will fl…

> Connect a 3 volt battery to a .01 ohm load (a dead short, almost) and 300 amps of current will flow

Except it won't, of course, because all real batteries have internal resistance. (How much depends on the battery chemistry and size.) Probably the 700mA rating for the AA battery is into a dead short.

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#36

Post by sbierwagen »

rflrob wrote: post #33
haldujai wrote: post #21

Original paper: doi: 10.1002/anie.201302577 From their paper it is mentioned they have a 40 nanolitre/min flow rate (25% desalination rate, 99% is considered safe to drink water). They use an electric pole to generate an ion depletion zone, their problem right now lies in the severely limited flow rate and desalination rate. From my understanding the 25% desalination rate does not compound linearly and decreases in e…

>Additionally their flow rate is 0.4 microlitres per minute, this would equate to needing 625 000 channels for one pass only to get 250mL / min. Scaling for microfluidics isn't simply using a larger pipe size, microfluidic devices largely operate with minimal forces and a Reynolds number of 1, that doesn't hold as you get larger. What about parallelization? Are there any obvious downsides to simply having lots of the…

Using 625 000 channels is parallelization. Those channels are in parallel.

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#37

Post by sbierwagen »

ars wrote: post #26
zw123456 wrote: post #5

It would be great if a Solar cell or small panel could power it. That could be a life saver in emergency situations.

The absolute minimum energy you need is 2.2kJ per liter. A 4x4 inch solar cell could do that in about 2 hours. However I suspect that you'll never actually desalinate water for that amount of energy in a portable system. The very best commercial systems manage to do it with about 3 times the energy of the minimum. More common ones are about 10 times the minimum.

  The absolute minimum energy you need is 2.2kJ per liter.
Where's that number from? For what process?

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#38

Post by haldujai »

rflrob wrote: post #33
haldujai wrote: post #21

Original paper: doi: 10.1002/anie.201302577 From their paper it is mentioned they have a 40 nanolitre/min flow rate (25% desalination rate, 99% is considered safe to drink water). They use an electric pole to generate an ion depletion zone, their problem right now lies in the severely limited flow rate and desalination rate. From my understanding the 25% desalination rate does not compound linearly and decreases in e…

>Additionally their flow rate is 0.4 microlitres per minute, this would equate to needing 625 000 channels for one pass only to get 250mL / min. Scaling for microfluidics isn't simply using a larger pipe size, microfluidic devices largely operate with minimal forces and a Reynolds number of 1, that doesn't hold as you get larger. What about parallelization? Are there any obvious downsides to simply having lots of the…

Yes, parallelization is actually the currently accepted means of increasing throughput, you'll see diagnostic devices with thousands of channels. The reason it isn't appropriate here is because of the complexity, the design is easy, you make a radial pattern of inlets with the splits towards the middle so you can combine outlets of the same type. Construction is relatively easy as well.

The problem comes from the number of inlets. You can:

a) a common inlet to all of your channels, or b) independent inlet for each channel, or for several channels

a) might seem intuitive, the problem is limitations on channel width, the inlet would have to feed a single channel which would then split (they would split to the inlet channel from the paper), structural limitations of PDMS and manufacturing have maximum widths and heights in millimetres at best. Which would not be enough to achieve the throughput required. The original 'master' inlet would probably have to be at least in the 10-20 cm range to achieve flow rates that could make this a household filter.

Even with another, stronger material, and perhaps manufacturing techniques I'm not aware of you still have limitations of pressure, their channels are very small in the paper (for a reason), pressure becomes a limiting factor to prevent their failure.

The problem with b is sheer complexity, you're talking about 10 000 tubes and connectors and holes punched into a chip if you even do a 1 - 60 split. The chip with just the channels would be about the size of a tissue box, this wouldn't be able to accomodate the channels so now you're talking about something tens of metres x tens of metres. This is hugely cost prohibitive and the channels from connectors would have to be really long, really long channels need more pressure to drive the liquid requiring more energy which reduces the efficiency significantly.

The reason parallelizaton works in pharmaceutical / DNA testing applications is you're going from microlitres of DNA/samples to nano, or picolitres in the channels, a single inlet can sufficiently provide that throughput (you're talking 10 uL / hour perfusion rates)

Edit: TL;DR version: Construction constraints would make this have worse efficiency than reverse osmosis and cost a lot more to manufacture as well.

Re: Chemists Work to Desalt the Ocean for Drinking Water, One Nanoliter at a Time

#40

Post by tsotha »

ars wrote: post #22
cmsmith wrote: post #17

Earlier quoted context omitted.

This is a great question. Distillation has the side effect of removing all of the microbes from water and sanitizing the output, but if this method only removes the salt will the output water be clean enough to drink?

Do you think they clean your local city water? They don't. They filter it a bit, then add chlorine to deal with biologicals, and that's it.

But municipal water typically comes from rain or snowfall. The distillation has already been done.
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