Which variables determine the exact output of this condensing device?

  • Thread starter anikad
  • Start date
  • #26
22
0
ffffs. The lengths people will go not to worry the pretty little heads with such inconveniences as "science" is unbelievable.


Yeah, and thanks loads for making me have to google for the original link.

Garbage article from google/x-company ; it does contain a larger resolution diagram of the device where - given an existing (but shallow) knowledge of the existence of desiccation dehumidifiers - it's easier to figure out what's actually happening

A directly related article/paper in Nature which looks possibly interesting and I might read tomorrow if the headache from looking at the crap article subsides.

It's a desiccant dehumidifier : they exist ; I think the "new" thing is the man-portable paradigm.

The inside air and the outside air do not mix.

There's a turntable (close to the B mark on the diagram) which contains a desiccant.

As it turns, outside air is blown across the surface, which sucks out some moisture because that's what desiccants do. (The outside air then leaves the device, never to be seen from, again).

It continues to turn, the slightly soggy surface passing through the curtain to the inside, where hot(ter) internal air is blown across it, evaporating some of the water. The particular patch of turntable we're looking at then returns to the outside as fresh, shiny and dry.

Meanwhile the inside air goes and does the heat exchange thing, which cools it and causes some of the water vapour to condense. It then returns (through the other side of the heat-exchange) to the turntable.

Yes, it works. The article says so, and even says the prototype does "150ml/h/m^2", though it mentions neither what the m^2 refers to (presumably one of either heating or desiccant surfaces), nor the environmental conditions under which the measurement/calculation took place.

Efficient ? compared to what ?

It doesn't look like a prototype so much as a proof of concept. In my pretty much totally uneducated-on-the-subject-matter opinion it could be done without the fans, though : probably less efficient, but niftier IMHO. On the other hand, you could use the (presumed) solar panels which run the thing to charge a cellphone to call for a pizza. That bit's efficient in respect that the waste heat from electricity generation is actually being used (to heat the internal air).

Not to denigrate the people who designed and put it together; I'm not going to pretend I could do it.
Thanks for the details.
If I'm correct, the following dependencies hold true as relating to condensate output:
1) The hotter the inside air blowing- the more it can extract moisture & the more the yield.
2) The more rounds of heat exchange process takes place per unit time, the more the yield.
3) The lower I can get the temperature of the ambient air on the bottom, the more the yield.

Is that true? If there's some physics wizard in here, an exact equation relating all those variables in the system would help massively!
 
  • #30
22
0
I recall there was a much older thread here that referenced the turntable dehumidifier, but I can't find it now.

Here are a couple slightly related threads that you might find interesting:
https://www.physicsforums.com/posts/6264085/
https://www.physicsforums.com/posts/6194175/

Cheers,
Tom
Thanks for sharing that!
If I understand correctly, these devices will not produce condensate at night , since there's no solar power to heat the turntable dessicant (and thus no temperature difference) ?
 
  • #31
Tom.G
Science Advisor
4,119
2,816
Thanks for sharing that!
If I understand correctly, these devices will not produce condensate at night , since there's no solar power to heat the turntable dessicant (and thus no temperature difference) ?
So oversize by a factor of 4. Unless you are in the Sahara desert or Australian Outback, the plants aren't likely to die of dehydration in one day!

(Have you figured out how you will prevent over-watering?)
 
  • #32
cmb
1,120
121
Summary:: I'm looking to discuss the main variables that define the output/yield of a Atmospheric water generator device.

Good day all:smile:!
I've been researching on 'Atmospheric water harvester' (AWH) devices.
As I researched many functioning mechanisms on such devices, the most workable mechanism to me seems to be the one illustrated in the picture attached to this thread. (i.e running hot humid air over cool air using renewable energy source & collect the condensing water output.)

So my questions are twofold:
1) Am I right in thinking that this mechanism could be the most efficient to harvest water with no outside interference?
2) And what are the main variables that would affect the condensing water output we can get ..
In my mind, I suppose: the more mass volume of both hot & cold air we can get in contact per unit time, the better the condensing output?

Thanks a lot in advance for your input!

P.S: I'm new to the forum, but I intend to stick around & be an active participant here!
Heating up a load of nitrogen/oxygen for no good reason is always going to be inefficient.

Likewise cooling them.

Whatever you think the process is doing and how it is doing it, you need to figure out an optimum solution to regenerate the thermal state of the gases you heat/cool, so you don't have to do that over again with the next 'charge' of gas.

You will only get condensate when the working volume you are manipulating drops below its dew point, so worth reviewing that too, maybe there is some means to do what you want but in a depressurised system? You'll have to figure out how to gate a sample charge of gas, lower the pressure, extract condensate, then recover the latent energy used to form the depressurisation.
 
  • #33
hutchphd
Science Advisor
Homework Helper
3,783
2,947
You will only get condensate when the working volume you are manipulating drops below its dew point, so worth reviewing that too, maybe there is some means to do what you want but in a depressurised system?

I agree (forcefully) that the originally system is not going to work at all, despite the OP entreaty to find an accomplice to defy the laws of known physics.
However this statement is overly broad. There are methods (usually involving changing effective dimensionality) to modify the kinetics for physical changes. For instance a catalytic converter can produce desired reactions on its 2D surfaces. Oxygen concentrators use surface reactions to pull nitrogen from the air in a cycle . The device I referenced in #27 above is similarly cyclic and probably relies on 2D surface kinetics.(?)
So there may be many ways to approach this problem, some may be simple, but none of them are easy.
 
  • #34
hmmm27
Gold Member
850
395
I agree (forcefully) that the originally system is not going to work at all, despite the OP entreaty to find an accomplice to defy the laws of known physics.
I would respectfully disagree with that, and not just because I'm the apparent "accomplice"😉

I don't see anything wrong with the theory, not qualified to comment on the engineering.

The system transfers water from the atmosphere to a bucket through two sequential fixed media : dessicant and internal air.

Warm air from the outside comes in, interacts with the dessicant and goes out, slightly drier. It has the dual purpose of cooling the dessicant and provides it with some moisture.

In an internal closed loop, very hot air picks up moisture from the dessicant and is moved to a cooler zone where it is cooled and deposits the moisture. It is then heated again, etc.

Note that while it's a continuous process, it might require quite a bit of apparently fruitless circulation before the internal air has picked up enough water to start condensing on the cooler surface.
 
Last edited:
  • #35
hutchphd
Science Advisor
Homework Helper
3,783
2,947
I was refering to the original design containing no dessicant.
Here I was in particular commenting on @cmb suggestion that a pressure change would be requiired. There may be other methods as well involving surface reactions using temperature directly.
 
  • #36
hmmm27
Gold Member
850
395
I was refering to the original design containing no dessicant.
This one ? (larger image from the article)
desiccant humidifier.png

I added in the purpl'ish arrows in the second-from-top level (missing from the original diagram) to illustrate ambient air movement. The round thing is what I thought was a flow-across turntable, but is apparently (or possibly) a flow-thru (turning) disk.

For the OP's possible edification, the tray with the heat-exchanger on it, the airflows are not actually mixing : inside the hexagonal structure, pipes that carry the airflows carry out the heat exchanging.
 
Last edited:
  • #37
cmb
1,120
121
Here I was in particular commenting on @cmb suggestion that a pressure change would be requiired.
Not something I said. I said "maybe there is some means to do what you want but in a depressurised system?".

Maybe there is some reason I seem to be routinely misread?

But anyway .... it was just a suggestion ...
 
  • #38
hutchphd
Science Advisor
Homework Helper
3,783
2,947
You will only get condensate when the working volume you are manipulating drops below its dew point, so worth reviewing that too, maybe there is some means to do what you want but in a depressurised system? You'll have to figure out how to gate a sample charge of gas, lower the pressure, extract condensate, then recover the latent energy used to form the depressurisation.
?This is not a pressure change ?
 
  • #39
cmb
1,120
121
?This is not a pressure change ?
Yes, but not 'required'. I proposed it as one possible means to help achieve necessary dew point.
 
  • #40
hutchphd
Science Advisor
Homework Helper
3,783
2,947
Apologies. I did not intend to offend or mischaracterize.
 
  • #41
cmb
1,120
121
No prob. I thought I was adding an alternative train of thought for the OP, didn't want to make an argument of it.
 
  • Like
Likes anikad and hutchphd
  • #42
22
0
I would respectfully disagree with that, and not just because I'm the apparent "accomplice"😉

I don't see anything wrong with the theory, not qualified to comment on the engineering.

The system transfers water from the atmosphere to a bucket through two sequential fixed media : dessicant and internal air.

Warm air from the outside comes in, interacts with the dessicant and goes out, slightly drier. It has the dual purpose of cooling the dessicant and provides it with some moisture.

In an internal closed loop, very hot air picks up moisture from the dessicant and is moved to a cooler zone where it is cooled and deposits the moisture. It is then heated again, etc.

Note that while it's a continuous process, it might require quite a bit of apparently fruitless circulation before the internal air has picked up enough water to start condensing on the cooler surface.
Thank you .
That's exactly what I've picked up from the original design. I'm working on a design based upon "batch processing" to prevent the highly inefficient water pickup of internal air.
 
  • #43
22
0
No prob. I thought I was adding an alternative train of thought for the OP, didn't want to make an argument of it.
Thank you for your input!:smile:
This is still confusing to me.
The condensate forms when there is a temperature difference ( for eg: ambient temperature on outside, & high temperature on inner closed area) .
What does the dew point has anything to do with condensate?
Can you please elaborate what I'm missing?
 
  • #44
hmmm27
Gold Member
850
395
What does the dew point has anything to do with condensate?
The Wikipedia article on "dew point" explains it quite clearly in the very first paragraph, IMHO.
 
  • Like
Likes anikad and Tom.G
  • #45
22
0
The Wikipedia article on "dew point" explains it quite clearly in the very first paragraph, IMHO.
I just did a little reading on dew point.
My intuition was: if we trap heat in a closed system, and continue saturating it with moisture- then we let the highly saturated air (that can't hold any more water vapors) come in contact with the wall of the system that is slightly cooler because it's in contact with outside ambient air- the condensate will start to form.

It seems my intuition was correct even without knowing/taking into account the dew point?.
 
  • #46
22
0
I agree (forcefully) that the originally system is not going to work at all, despite the OP entreaty to find an accomplice to defy the laws of known physics.
However this statement is overly broad. There are methods (usually involving changing effective dimensionality) to modify the kinetics for physical changes. For instance a catalytic converter can produce desired reactions on its 2D surfaces. Oxygen concentrators use surface reactions to pull nitrogen from the air in a cycle . The device I referenced in #27 above is similarly cyclic and probably relies on 2D surface kinetics.(?)
So there may be many ways to approach this problem, some may be simple, but none of them are easy.
Hey hutchphd, this is not an attempt to defy the laws of physics.
Perhaps, you didn't understood the mechanism of the device correctly?
If you can prove which law is being defied in the device, I'd take account.:smile:
 
  • #47
256bits
Gold Member
3,529
1,538
Hey hutchphd, this is not an attempt to defy the laws of physics.
Perhaps, you didn't understood the mechanism of the device correctly?
If you can prove which law is being defied in the device, I'd take account.:smile:
Well, you just can't say this is how it works and I can get water from air.
There is ( probably ) a limited temperature / humidity levels of the outside air, and heating from the sun, where the system will complete it's function as planned.

The air at the cool surface has to be at 100% humidity for condensate to form.
For example,
If the outside air is at 20 C 30% RH your cooling surface will be at 20 degrees also, since you are not actively cooling that surface.
If you can get the cooler air up to 100% humidity then well you will have condensate.
Then ask yourself the question, how much heat needs to be added to the air at the top section so that the RH of the top hot air is less than 30% for the wheel to transfer moisture from the ambient air to the wheel to the hot air. What is that temperature? If the temperature does not reach that level then the wheel ends up working in reverse and transferring humidity from the hot air to the outside air.
Suppose the temperature rises just 1 degree about that needed just below < 30% humidity.
Then the system does do as planned, but the yield amy be a drop an hour <-- just a simple guess.
You will have to look at your psychometric chart to get answers.

You really have to do an engineering analysis, to determine at what temperatures and RH's where the system can do something useful.

Here's a start.
https://www.odellassoc.com/how-do-desiccant-dehumidifiers-work/
https://www.trane.com/content/dam/T...wsletters/airside-design/admapn016en_0905.pdf
 
  • #48
hutchphd
Science Advisor
Homework Helper
3,783
2,947
Hey hutchphd, this is not an attempt to defy the laws of physics.
Perhaps, you didn't understood the mechanism of the device correctly?
If you can prove which law is being defied in the device, I'd take account.:smile:

I added in the purpl'ish arrows in the second-from-top level (missing from the original diagram) to illustrate ambient air movement. The round thing is what I thought was a flow-across turntable, but is apparently (or possibly) a flow-thru (turning) disk.
This version can work. Purple arrows.
 
  • #49
22
0
The air at the cool surface has to be at 100% humidity for condensate to form.
For example,
If the outside air is at 20 C 30% RH your cooling surface will be at 20 degrees also, since you are not actively cooling that surface.
If you can get the cooler air up to 100% humidity then well you will have condensate.
Then ask yourself the question, how much heat needs to be added to the air at the top section so that the RH of the top hot air is less than 30% for the wheel to transfer moisture from the ambient air to the wheel to the hot air. What is that temperature? If the temperature does not reach that level then the wheel ends up working in reverse and transferring humidity from the hot air to the outside air.
Suppose the temperature rises just 1 degree about that needed just below < 30% humidity.
Then the system does do as planned, but the yield amy be a drop an hour <-- just a simple guess.
Thank you! Now you really appear to be my accomplice:biggrin:.

So the engineering analysis of this system comes down to this : The greater the temperature difference between hot air & cooler ambient air, the quicker the air picks up enough moisture to reach 100% humidity- to be brought to a cooler surface.


Am I thinking correctly?
 
Last edited:
  • #50
hutchphd
Science Advisor
Homework Helper
3,783
2,947
Also the choice of dessicant will make a big difference I believe. I found this interesting: a clever guy trying to make a desiccant-based air conditioner:



It didn't work all that well !
 
  • Like
Likes 256bits and anikad

Related Threads on Which variables determine the exact output of this condensing device?

Replies
5
Views
1K
  • Last Post
Replies
2
Views
1K
J
Replies
3
Views
3K
  • Last Post
Replies
12
Views
2K
Replies
3
Views
1K
Replies
1
Views
12K
  • Last Post
Replies
8
Views
5K
Replies
33
Views
6K
  • Last Post
Replies
3
Views
2K
Top