Moisture Farms
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06-05-2017, 11:13 AM
RE: Moisture Farms
(05-05-2017 06:45 AM)Carlo_The_Bugsmasher_Driver Wrote:  Sniff, Sniff, Sniff.......

I smell bullshit.

Yes, yes this idea is pure bullshit.

Given the energy and performance requirements necessary for this kind of Peltier moisture capture system, it's an unreasonable and expensive design. For the money, you would be better off airdropping containers of tapwater into arid regions to provide drinkable water than using this device.

I had wanted to wax endlessly about this damn thing but Thunderf00t beat me to it.



Peer-reviewed or it didn't happen.

Feel free to wax but I'll take a paper in Science over social media.

Given the high-profile nature of this announcement one might reasonably expect the claim to have been examined by scientists in the same field and debunked as necessary. I'm seeing precious little of that.

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06-05-2017, 11:18 AM
RE: Moisture Farms
(05-05-2017 11:22 AM)SYZ Wrote:  Solar still anybody...

[Image: 27aec62b8e2096c49c6a06e09c234bfd.gif]

Worth about 10¢ and can produce (possibly) 1 litre of water per day—dependent on size of plastic sheet and amount of sunlight.

Works fine so long as you have high humidity. Vegetation was used for that in the diagram. Lacking that you have a plastic sheet, empty can and a hole in the ground.

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08-05-2017, 03:34 AM (This post was last modified: 08-05-2017 07:46 AM by Carlo_The_Bugsmasher_Driver.)
RE: Moisture Farms
(06-05-2017 11:13 AM)Paleophyte Wrote:  
(05-05-2017 06:45 AM)Carlo_The_Bugsmasher_Driver Wrote:  Sniff, Sniff, Sniff.......

I smell bullshit.

Yes, yes this idea is pure bullshit.

Given the energy and performance requirements necessary for this kind of Peltier moisture capture system, it's an unreasonable and expensive design. For the money, you would be better off airdropping containers of tapwater into arid regions to provide drinkable water than using this device.

I had wanted to wax endlessly about this damn thing but Thunderf00t beat me to it.



Peer-reviewed or it didn't happen.

Feel free to wax but I'll take a paper in Science over social media.

Given the high-profile nature of this announcement one might reasonably expect the claim to have been examined by scientists in the same field and debunked as necessary. I'm seeing precious little of that.

You DEMONSTRATE that device can deliver those kinds of water yields in arid conditions using the parameters they describe and I'll believe it. Until then the established science of thermodynamics says this is highly unlikely.

Oh, and 95% of scientific papers are eventually proven false or at least impractical as I'm quite sure this one will be.

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08-05-2017, 08:34 PM
RE: Moisture Farms
(08-05-2017 03:34 AM)Carlo_The_Bugsmasher_Driver Wrote:  You DEMONSTRATE that device can deliver those kinds of water yields in arid conditions using the parameters they describe and I'll believe it.

Me too. I'll believe it when I see it but I'm going to be excited about the potential.

Quote:Until then the established science of thermodynamics says this is highly unlikely.

According to who? Thunderf00t's good at melodrama but fails basic science and integrity. Major problems with his analysis included:

- Failing to check with the researchers themselves. That's basic journalistic integrity and the starting point for investigating a dubious claim. You can't debunk what you don't properly understand but he goes off and makes a bunch of assumptions rather than doing the ground truthing. As a scientist himself he's in a precarious position having just called fellow scientists' work "bullshit" based largely on his misunderstanding. It's a measure of how poorly the scientific community regards him that they won't bother holding him to that standard. I was amused by the way he ended the video, "'Cause I am the one who checks."

- His big reveal about the Peltier device is labelled in Figure 2 of the paper as "Thermoelectric cooler". It's necessary in the prototype because it's too small to form water droplets otherwise. I suppose all the melodrama was better for Youtube ratings.

- Despite trying to look sciency he utterly missed the entire point of the paper which is summed up in the final sentence. The MOF is an order of magnitude more efficient than traditional dessicants. That is what allows it to run solely on solar and makes his demos with the zinc chloride and yap about tanker trucks (and from where will you truck it, dear Liza, dear Liza) nothing more than pointless strawmen.

- He carried on a lot about the thermodynamic impossibility and did back of the envelope calculations for everything else. The two never seemed to meet though. Why do you suppose that is? Let's be good skeptics and not take anybody's word for it.

The prototype extracted less than 1 mL of liquid water over a 3 hour period. For back of the envelope calcs let's call it 1 mL even. For water at STP, 1 mL is 1 gram or close enough. Water has a latent heat of vaporization of 2264 J/g and your heat sink has 3 hours to dump that. That means that your heat sink has to radiate at 2264 J / 10800 s = 210 milliWatts. Are you certain that's a thermodynamic impossibility? Because I'm thinking that a passive heat sink backed by a 25 C thermal gradient should be able to beat that by an order of magnitude or two.

Now if you want to get into scalability, cost of MOF synthesis, or lifespan of the MOF that's another kettle of fish. I think that they'll run into trouble, but that's hardly unexpected with new tech like this.

Quote:Oh, and 95% of scientific papers are eventually proven false or at least impractical as I'm quite sure this one will be.

Would the one that statistic came from be amongst that 95%? Tongue

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10-05-2017, 12:18 AM (This post was last modified: 10-05-2017 12:33 AM by Carlo_The_Bugsmasher_Driver.)
RE: Moisture Farms
Quote:- Failing to check with the researchers themselves. That's basic journalistic integrity and the starting point for investigating a dubious claim. You can't debunk what you don't properly understand but he goes off and makes a bunch of assumptions rather than doing the ground truthing. As a scientist himself he's in a precarious position having just called fellow scientists' work "bullshit" based largely on his misunderstanding. It's a measure of how poorly the scientific community regards him that they won't bother holding him to that standard. I was amused by the way he ended the video, "'Cause I am the one who checks."

- His big reveal about the Peltier device is labelled in Figure 2 of the paper as "Thermoelectric cooler". It's necessary in the prototype because it's too small to form water droplets otherwise. I suppose all the melodrama was better for Youtube ratings.

When you state in the opening thesis that such a device would condense water out of thin air with no additional energy input - a statement which violates just about everything we know about thermodynamics and psychrometrics - that WILL raise eyebrows with any competent scientist. In order to condense water vapor into liquid water, you have to remove the energy from it; there's just no other way to accomplish this. Anyone claiming otherwise HAD BETTER DEMONSTRATE THEY CAN WITH A REPEATABLE EXPERIMENT because there's a mountain of data about our universe which says otherwise.

Quote:The prototype extracted less than 1 mL of liquid water over a 3 hour period. For back of the envelope calcs let's call it 1 mL even. For water at STP, 1 mL is 1 gram or close enough. Water has a latent heat of vaporization of 2264 J/g and your heat sink has 3 hours to dump that. That means that your heat sink has to radiate at 2264 J / 10800 s = 210 milliWatts. Are you certain that's a thermodynamic impossibility? Because I'm thinking that a passive heat sink backed by a 25 C thermal gradient should be able to beat that by an order of magnitude or two.

Sure, lets do a basic back of the envelope calculation for such a device based on a practical system for delivering water. Let's take the claimed numbers which the paper states in its thesis:

"This device is capable of harvesting 2.8 liters of water per kilogram of MOF daily at relative humidity levels as low as 20%, and requires no additional input of energy."

Unless the author's can demonstrate the claim that this device can condense water from thin air without expelling the energy and thereby violating the second law of thermodynamics, we have to use their original setup which yielded moisture and that required a surface chilled using a Peltier device. We will use a Peltier device for condensation in our calculations.

On a per kilogram basis for this MOF substance and considering ONLY the energy needed to condense this water:

2800 g H2O x 2264 J/g = 6.34 MegaJoules

Typical high efficiency Peltier cooling systems only run at about 50% efficiency, so this setup requires 12.68 MegaJoules of input energy in order to operate.

In a 24 hour day, we need a power supply of 12680000 J / 86400 s = 146.7 W or 528 kW-h in order to achieve these figures.

Typical electrical rates are around $0.12/kW-h so the system (in just operating costs) costs $63.39 per day or about $22.64/liter of water!

or about $45,280 per metric ton!

As a yardstick for comparison, tapwater costs on average $1.50 / 1000 gallons (3,785 liters), or roughly $0.79 per metric ton.

Typical ground shipping rates are around $0.30 / kg so to ship 1 metric ton of tapwater will run about $600 or be about 75 times cheaper than using this asinine MOF scheme.

Even air freight rates are slightly less than $3/kg these days. One could even airdrop a container with a metric ton of water for about $6000 or about 7.5 times cheaper than the MOF system.

And that's why these Peltier dehumidification systems have been on the market for decades but never utilized in this capacity.

Using a passive heat sink? Now show me a natural heat sink in a desert at 30°C which is 5°C above freezing. Wish in one hand and shit in the other and see which fills faster.

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11-05-2017, 05:18 PM
RE: Moisture Farms
(10-05-2017 12:18 AM)Carlo_The_Bugsmasher_Driver Wrote:  We will use a Peltier device for condensation in our calculations.

Have fun with that. I'll do mine without.

Quote:2800 g H2O x 2264 J/g = 6.34 MegaJoules

6.34 MJ / 12 hrs = 147 Watts

At rest, the human body radiates ~100 Watts with a 1-2 m2 area more or less passively with a 12-15 degree C thermal gradient with the ambient air. That's unsurprising given that a couple MegaJoules is your average daily dietary intake.

Scaling up their prototype to 1 kg will make the MOF layer ~1.75 m2 assuming you don't change the thickness so you'll have plenty of space for the passive heat sink in the shadow of that.

Still not seeing a violation of thermodynamics here.

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12-05-2017, 04:39 AM (This post was last modified: 12-05-2017 06:17 AM by Carlo_The_Bugsmasher_Driver.)
RE: Moisture Farms
(11-05-2017 05:18 PM)Paleophyte Wrote:  
(10-05-2017 12:18 AM)Carlo_The_Bugsmasher_Driver Wrote:  We will use a Peltier device for condensation in our calculations.

Have fun with that. I'll do mine without.

Quote:2800 g H2O x 2264 J/g = 6.34 MegaJoules

6.34 MJ / 12 hrs = 147 Watts

At rest, the human body radiates ~100 Watts with a 1-2 m2 area more or less passively with a 12-15 degree C thermal gradient with the ambient air. That's unsurprising given that a couple MegaJoules is your average daily dietary intake.

Scaling up their prototype to 1 kg will make the MOF layer ~1.75 m2 assuming you don't change the thickness so you'll have plenty of space for the passive heat sink in the shadow of that.

Still not seeing a violation of thermodynamics here.

You mean besides expecting this energy to be extracted from the water vapor in the air in a hot environment without the use of additional energy to do so? You don't see the violation of the Second Law of Thermodynamics in that?

The problem is that heat sink, even in shadow won't reach the dew point of the air in that kind of a hot, arid environment. No dew point, no condensation, it's as simple as that.

What drives my bullshit o'meter through the roof is that, if it was that simple to do so as these guys claim, WHY THE HELL DOESN'T THE RESEARCH TEAM WHO WROTE THE PAPER MAKE AN EXPERIEMNTAL APPARATUS IN THAT CONFIGURATION AS OPPOSED TO USING A PELTIER DEVICE REQUIRING AN ENERGY INPUT?

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12-05-2017, 05:34 PM
RE: Moisture Farms
Probably because it was a prototype that was slapped together in a hurry.

*meh* Time will tell.

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