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# Water From Air

04/19/2016 12:01 AM

I'm interested in harvesting water from fog or air exceeding 40% relative humidity for irrigation purposes. Some have already done this on a small scale. Can anyone tell me the best way to force dew point? Is it pressure? Temperature? Surface conductivity? Or is the draw off of the condensate the limiting factor? My plan is to build a prototype and experiment with variables over the coming year. Thanks for your help!

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#1

### Re: Water From Air

04/19/2016 12:12 AM

Research "Dew Point" and find out what it is!

Also look at "humidity" while you are at it!

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#5

### Re: Water From Air

04/19/2016 12:47 AM

I have researched dew point. I have also spent considerable time understanding relative humidity. How about you check out "Fog Harvesting" from MIT and learn how they irrigate complete villages with a passive net system. Then come back and let's discuss how to actually make it happen. Or not...

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#8

### Re: Water From Air

04/19/2016 2:11 AM

Did you read the simple definition:

The
dew point (dew point temperature or dew point) is the temperature at which dew forms and is a measure of atmospheric moisture. It is the temperature to which air must be cooled at constant pressure and water content to reach saturation.

In your research did you find any dew point charts? The basic physics is easy accessible.

This is what you asked in your OP. Now you want to irrigate complete villages with this system that you want to develop. Good on Ya!

I come back now and have another question: What is a passive net system???

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#37

### Re: Water From Air

04/20/2016 11:27 AM

... from that ol' "For-What-It's-Worth" department ... ever since my NACE training in the field of protective coatings, I have understood the "simple definition" to be much-too-obfuscating.

As I seem to recall, technically speaking, when conditions are "exactly-precisely-AT" the dew point, water will condense on a surface at the same rate at which it evaporates.

When the temp falls below the dew point, excess liquid will form on (surfaces).

Let's kick the OP off without ANY "misdirection", here...

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#38

### Re: Water From Air

04/20/2016 12:10 PM

Yes, in his case, he must be below dew point to realize any yield of significance.

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#2

### Re: Water From Air

04/19/2016 12:17 AM

This is not a very productive or reliable way to produce water, nor is it likely to be sufficient for crop growth...The best way is to find the nearest water source that is sustainable and available...

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#4

### Re: Water From Air

04/19/2016 12:44 AM

Thanks for your thoughts. It's good to know that condescension and arrogance are not yet dead. I can only imagine your encouragement to Benjamin Franklin, the Wright Bros., Nikolai Tesla, Albert Einstein, Copernicus or Isaac Newton for their ideas that were equally stupid and fruitless...before the fact! If you have a positive comment to contribute I would welcome your input. Otherwise, please leave the groundbreaking to the fearless and positive thinkers.

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#16

### Re: Water From Air

04/19/2016 6:24 AM

There's no need for that.

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#18

### Re: Water From Air

04/19/2016 10:28 AM

I don't think those mentioned needed any encouragement, they were all rather single minded in their individual pursuits, and I recognize a good idea when I see one, generally speaking of course....I didn't say your idea was stupid and fruitless, though indeed you may be, but that the methods I've seen and heard about or read about, have not been very productive or reliable...

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#33

### Re: Water From Air

04/20/2016 10:07 AM

You probably have not seen the 'system diagram' for an engineer. Treating the Engineer as a 'black box' with inputs and outputs, you get the following chart:

• Input 1: Problem
• Input 2: Coffee
• Output (desired): Solution
• Output (waste): Sarcasm

You can do this with anything, for example, an air compressor would have the following chart:

• Input 1: Low-Pressure Air
• Input 2: Electricity
• Output (desired): Compressed Air
• Output (waste): Heat
• Output (waste): Noise

We can also rank the outputs by quantity, which can lead to more accurate descriptions:

• Input 1 (largest): Electricity
• Input 2 (smallest): Low-Pressure Air
• Output 1 (largest): Heat
• Output 2 (second largest): Noise
• Output 3 (smallest): Compressed Air

From those inputs and outputs, we can better define an Air Compressor as a 'noisy electric furnace.' When you rank the inputs and outputs of an Engineer, you see something rather interesting:

• Input 1 (largest): Coffee
• Input 2 (smallest): Problem
• Output 1 (largest): Sarcasm
• Output 2 (smallest): Solution

"I can only imagine your encouragement to Benjamin Franklin, the Wright Bros., Nikolai Tesla, Albert Einstein, Copernicus or Isaac Newton for their ideas that were equally stupid and fruitless...before the fact!"

You act as if these great men were never laughed at before their big success. Every great idea get laughed at at first.

"If you have a positive comment to contribute I would welcome your input. Otherwise, please leave the groundbreaking to the fearless and positive thinkers."

I have a positive comment for you: If you wish to succeed in Engineering, you need to grow two things; a thick skin, and a sense of humor. Your peers will always try to tear into and tear apart your ideas, it's called 'peer review,' and it's how we discover the hidden flaws. Good discussion between Engineers are about each one finding the ways the other's ideas will not work, so one of them, or perhaps a third Engineer, can refine that section so it WILL work. We never(1) engage in ad hominem attacks, where we tear into each other. And we do not take an attack on out pet project as an attack on our person. great ideas and great men are always laughed at in the beginning, that's just part of life.

"The fact that some geniuses were laughed at does not imply that all who are laughed at are geniuses. They laughed at Columbus, they laughed at Fulton, they laughed at the Wright brothers. But they also laughed at Bozo the Clown." -Carl Sagan, Broca's Brain (1979), p. 64 ISBN 0394501691 (via Wikiquote)

In closing, welcome to CR4.

Notes:

1. Well, almost never. We are still human, and have human failings, and sometimes we verbally attack the other person instead of the idea. But when we are called out on it, we tend to be ashamed and contrite, apologizing for the offense, and redoubling our efforts not to repeat the mistake in the future.
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#13

### Re: Water From Air

04/19/2016 4:58 AM

Agree to disagree!

Found this.

Seems there is some ways of doing it!

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#17

### Re: Water From Air

04/19/2016 10:19 AM

If you would take time to read your own link you would see that these plastic covers are used in conjunction with regular watering, not in place of....Plastic coverings are not new, they use them down here for tomatoes and other delicate crops to control weeds and preserve moisture and root temperature for a shorter grow time and longer growing season....

I didn't say you can't produce water from the air, just that passive methods alluded to are not known to be very productive or reliable....Now if the OP has some new method that is, well he can share it with us all....

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#23

### Re: Water From Air

04/19/2016 10:55 PM

I mainly quoted it for the first sentence:

The ancient Israelites used stones to collect dew from the air, ...

That's about it. Its the ancient method. I don't think OP did understand the basic physics. Forcing the Dew point for me is cooling.

But getting enough output might be related to collection area and temperature changes. I find it particular funny that the question is asked for 40% or more humidity. Seems like there is a need for an uncontrollable initial condition.

Sorry I read your comment like it was not possible at all! But I agreed and yet disagreed, didnt I?

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#31

### Re: Water From Air

04/20/2016 8:01 AM

The reference to the stones reminded me of the sight 40 years ago of the bare ground in Jordanian fields covered in stones in preparation for planting. My first thought was how it would help the farmers to employ an efficient method of separating stones from soil - now I realise that would have been completely counter productive.

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#34

### Re: Water From Air

04/20/2016 10:47 AM

I am sure they can modify the surface texture of the tray (as some insects have done) to gain even more efficient collection of dew. One of my uncles used to simply throw up deep beds on sandy loam tracts where there was no irrigation, and claimed he could plant sorghum after a heavy dew and get a "stand".

Collecting moisture from the air takes full knowledge of the daily cycle of water content (not simply relative humidity) in the air. If warm air of low humidity is used, even if dew point is reached, not much will yield. If cold, high humidity air is used, again, not much yield. It really does take warm to hot air of high humidity (>40%) to really get much yield at all. The quantity of air to be cooled to dew point and passed on much increase as an inverse function of moisture content (not relative humidity).

I have heard of piling up roundish stones in a pyramid, with a water collection drainage system at the bottom middle. The daily cycling of temperature and moisture content is sufficient to cause condensation in the early morning hours to middle morning, I believe. At night, the stones cool off again for the next cycle, but there must be moisture laden air, and probably also requires a prevailing wind that sources from a large body of water.

I have seen heavy dew forming on cactus or yucca needles (concentrates the electric field?) in the desert area east of El Paso, Texas in the mountains, in winter conditions at times when no rain is in the forecast. This appears to be one of the secrets of nature.

To get the most out of whatever cooling tonnage you will have available, you must utilize (1) heat exchanges with the incoming and outgoing air to not waste the effect, and (2) you must be sufficiently below dew point that the driving force for condensation will further reduce equilibrium vapor pressure. If one has a source of waste water that needs recycling to potable water (and it has already been processed to the point of reduction of pathogens), it might be possible to "tip the scales" by using solar heat to evaporate some of this water and load up the incoming air.

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#3

### Re: Water From Air

04/19/2016 12:34 AM
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#6

### Re: Water From Air

04/19/2016 12:52 AM

Yes I know - I've read the latest on Fog Harvesting. Why do you say it can't be done in a volume larger than a room? I'm thinking of compressing the air into a refrigerator-size device, pre-heating the air intake and doping the air with moisture from the surrounding air. The hot, compressed, wet air hits a condensing coil (or glass-coated cooling tubes) and the water sheds to a collecting area. Tubes are cooled by earth depth. Pressure and heat are supplied by solar (free!). Why is this not practical?

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#7

### Re: Water From Air

04/19/2016 1:08 AM

Well, some detail is good.

"Refrigerator-size" devices to do what you want are called dehumidifiers.

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#9

### Re: Water From Air

04/19/2016 2:53 AM

Water Aid, one of the UK's leading charities, already uses fog harvesting in the Himalayas as a showcase example of low-tech solutions that provide water in remote communities across the globe.

Water sources are evaluated economically in terms cost per unit volume delivered. So it may prove more practicable to abstract river water and treat it in some places, abstract borehole water in others, fog-harvest in others and desalinate elsewhere - it depends upon the local circumstances.

There is nothing impractical in the posted suggestion; it is economics that determines viability in the arena in which the technology might compete.

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#10

### Re: Water From Air

04/19/2016 3:26 AM

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#11

### Re: Water From Air

04/19/2016 3:31 AM

If you want to understand air, you us a psychrometric chart.

It you want to understand insanity, you use a psychometric chart.

The OP seems to be confused between the two.

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#14

### Re: Water From Air

04/19/2016 5:00 AM

Thanks Legolas alias what ever it is now for the unnecessary comment!

It is you isn't it?

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#12

### Re: Water From Air

04/19/2016 4:41 AM

I have seen a water collection system in northern Chile (Atacama desert) where a barrier of plastic foils has been placed to condensate water from the nearby Pacific Ocean fog. These guys are called "Atrapanieblas" (Fogcatchers"): Search BBC Mundo / atrapanieblas. There is also a beer brewery which produces 24,000 litres of "fogwater" beer.

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#19

### Re: Water From Air

04/19/2016 11:00 AM

This is an area that has very heavy fog on a regular basis...try it without the fog....and I might also add this is not the dessert, but at the edge of the dessert...

http://www.gizmag.com/how-the-fogcatchers-of-the-atacama-are-bringing-water-to-the-driest-desert-on-earth/39040/

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#35

### Re: Water From Air

04/20/2016 10:54 AM

This is true that in Chile, at the Atacama desert, the ocean moisture is high at the coast, and is foggy much of the time, but the fog lacks the energy to rise over the coastal ridge line, hence the driest place on earth exists. Yes, use solar energy to drive a fog collecting system at the coast, and to pump the condensate uphill. That is a no brainer, or at least a low brainer.

Here in the U.S. we have a place called Foggy Bottoms (Washington, D.C.) and it is the source of all manner of unpleasant things including congressional flatulence.

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#15

### Re: Water From Air

04/19/2016 5:06 AM

Last hint for you. Do your own homework!

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#20

### Re: Water From Air

04/19/2016 2:47 PM

You might look into the actions of the Namib Dessert Beetle that stands on it's head to extract water from fog. Clever little blighters and a wonderful example of Darwinan evolution:

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#21

### Re: Water From Air

04/19/2016 4:01 PM

Are you suggesting they all stand on their heads and wave their legs around to gather water?

OMG it's working!

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#22

### Re: Water From Air

04/19/2016 4:09 PM

Damn it - it's all been done before. You are ahead of the game - as usual (he wrote begrudgingly).

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#24

### Re: Water From Air

04/20/2016 12:27 AM

Hello Bruce Schwandt,

I read a few of the replies to your post, and decided not to go further. The members here are not generally mean or arrogant, and I think that you are not being rational with some of your responses. Even so, I am offering my 2 cents worth as a professional engineer, without bias:

There are certainly methods for doing this, and they can certainly be improved, etc.

Removing water from air can be done by decreasing the temperature of a surface below the dew point so that condensation will occur. Therefore, you are going to have to input energy to do this.

The amount of water you will obtain from the air is dependent on how much air you are able to process and what the temperature difference is between the condensing surface and the ambient air.

If you want to condense more water, therefore you will have to increase the airflow, meaning the use of fans, blowers or somesuch (requiring more energy), and/or decrease the temperature of the condensing surface (requiring more energy).

My conclusion is this: you may be able to minimally supplement the watering of even the smallest of crops with such a scheme, but you will create a process that will create more headaches than the implementation of such a scheme is worth.

Peace, out

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#25

### Re: Water From Air

04/20/2016 1:02 AM

Few years ago I was the technical consultant to develop Water from Air Unit in Oman. Water from Air' unit was developed using condensation principle powered by conventional electrical energy. The unit was designed to ensure the extract of water minimum of 15L/day even at worse case conditions (20°C DBT, 55% RH). The prototype unit comprises a compressor, evaporator, condenser, Expansion Device control unit and other accessories with water collection tank. It was decided to use commercially available compressors and design the rest of the system. The design of evaporator and condenser with aluminium fins and copper coils were calculated using. Log Mean Temperature Difference (LMTD) method. The suggested dimensions were used to draw design drawing of the unit. The operating hours are limited to 12 hrs, instead of 24 hrs per day. Because it is evident that the extraction would be better between evening and next day morning than the day time. So, it has been decided to operate the unit for 12 hrs per day, in which it should yield 15 liters of water during nominal weather conditions (other than 5% of hours in a year). The unit was tested for various atmospheric conditions and it was found to be capable of producing 15 lits/day of water even in the worse condition. We submitted the complete report and their copy right to the sponsor who initiated the project. Many Such units are available commercially.

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#26

### Re: Water From Air

04/20/2016 1:12 AM

mrswamy,

What was the energy consumption of such a unit?

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#27

### Re: Water From Air

04/20/2016 1:22 AM

Since unit is based on conventional VC system it is energy intensive. I explained this energy aspect to the industry who sponsored this project; but their interest to generate water from air in desert for irrigation purpose and energy is the secondary aspect.

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#28

### Re: Water From Air

04/20/2016 2:41 AM

What I am asking is: how much energy does it take to produce 15L of water by this process? Either you can tell me, or your previous posts are suspect.

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#32

### Re: Water From Air

04/20/2016 9:07 AM

I have a 700 watt dehumidifier that is rated for 40 pints of water a day....The rate of water production is dependent on the humidity level...A relative humidity of >70% yields good water quantity.... <50% considerably less....

http://www.wholesalesolar.com/1440800/four-star-solar/battery-backup-systems/four-star-solar-backup-power-central-1000-120vac

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#29

### Re: Water From Air

04/20/2016 4:05 AM

There are bottles available which extract water from the surrounding air.

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#30

### Re: Water From Air

04/20/2016 7:30 AM

I don't know what the efficiency of a Peltier effect device would be. I imagine that to use the effect on a large scale would be expensive

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#36

### Re: Water From Air

04/20/2016 11:10 AM

Consider the Einstein-Szilard refrigerator. It uses low grade heat to produce the cold temperature, can be scaled up, etc. Ammonia cycle driven by heat produces a similar, maybe even superior CoP. Pick the cycle with the highest CoP, and dive in!

Obviously: Heat will evaporate water. If you have a down-graded water source unsuitable for irrigation (seawater for example), or highly saline well water, evaporation is an option, but the heat needs to be high enough (without using fuel) to achieve efficient loading of the air to be chilled downstream. You have to manage the heat, otherwise, you will not achieve efficient results, and require too large a heater and too large a chiller.

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#39

### Re: Water From Air

04/20/2016 5:01 PM

Advice given to me years ago. Get 3 No's, go for it. Get 2 Yes, forget it and find another idea.

A material with good superhyrdrophic surface would work well for complete water gathering.

And keep this in mind, no fog, you obtain fog all..

http://www.dailymail.co.uk/sciencetech/article-2636078/Now-THATS-waterproof-Super-material-repels-water-strongly-causes-liquid-droplets-BOUNCE-off.html

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#40

### Re: Water From Air

04/20/2016 5:51 PM

Hydrophobic would keep water away; hydrophilic would attract it.

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#41

### Re: Water From Air

04/20/2016 5:52 PM

In that case, go for the gold--hydromanic!!

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#42

### Re: Water From Air

04/20/2016 8:21 PM

No sir, it means water does not adhere and rolls off easily. What he needs.

If the water adheres it does not flow and is rather absorbed to his fog net, (moisture catcher) until it is saturated then it flows. The less absorption the more he gains in his reservoirs.

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#43

### Re: Water From Air

04/21/2016 8:21 AM

I tend to agree with IQ on this one. In a power plant condenser (as mentioned in the Utah link), sheeting of condensate on the condenser tubes is bad, and slows down heat transfer. Droplets forming and instantly rolling off is a much better, more efficient result.

The surfaces can be arranged (by curvature) to channel the droplets down to a collecting point and be drained away as they coalesce. This instantly makes more surface available to transfer energy and condense droplets.

What would be even better? A super hygroscopic material that absorbs moisture from the air, then would release it quickly when heated to some moderate temperature. Various sulfate salts have been looked at the past, but I think all of them require some serious heat near 100 C to effectively release the captured water (that still needs to be condensed elsewhere).

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#44

### Re: Water From Air

04/21/2016 10:28 AM

Depends on what power and equipment you have available - and the scale of the operation.

Basically 4 methods I know of.

1 Cool the air below ambient dewpoint and collect the condensate.

2 Compress the air to raise the dewpoint, then use ambient air to cool it below dewpoint.

3 Use a desiccant to absorb the vapour at ambient then heat the desiccant to drive the off the moisture, cool it with ambient air, and collect the condensate.

4 Investigate the use of modern reverse osmosis membrane techniques - I don't know this can be done.

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#45

### Re: Water From Air

04/21/2016 11:16 AM

Nice meeting you Mr. Horace and Mr. Stewart! I've been kinda too busy to post lately but I will post again later today. In the meantime if you could check out the work published by Xen Heng and Cheng Luo from UT Arlington "Bioinspired Plate-based Fog Collectors I'd like to discuss and lay plans for a field test on my property in the coastal desert of Southern California. There's also some more recent followup work published this year.

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#46

### Re: Water From Air

04/21/2016 11:35 AM

That is a fairly "sharp" approach. Even beaky!

I would have gone for a nano-topographic hydrophobic surface as collector, and something like a chamois cloth for a harvester surface, then simply wring it out to a container. After that, beauty is in the eye of the beholder.

This is to say that the small beads of condensate forming will not be large enough to roll off the surface at any particular angle of elevation. Beaks can transfer the water without "messing" with the specially prepared surface, so that is a plus, and may in fact require less energy than cloth wiping and wringing.

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#47

### Re: Water From Air

04/21/2016 6:05 PM

How do I upload a JPG from my desktop? Dragging and dropping just gives a text line below: /Users/bruceschwandt/Desktop/Condenser.JPG

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#48

### Re: Water From Air

04/21/2016 10:35 PM

Drag and drop generation unable to use tool bars?

Or wrong browser.

Try this.

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#49

### Re: Water From Air

04/22/2016 4:02 AM

Click the camera icon in the reply screen & then browse for the file.

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#50

### Re: Water From Air

04/22/2016 10:24 AM

Use the green camera in reply window (you need to be using something other than Safari for a browser, Pale Moon, perhaps, but certainly Firefox (I am using).

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#51

### Re: Water From Air

04/23/2016 12:59 AM

According to the United Nations Food and Agricultural Organization and the Centre for Development and Environment of the University of Bern, Fog Harvesting is considered a "promising option for adaptive water management" precisely because it is practical and reliable compared to other sources (such as digging a well) in regions where rainfall is scarce. Many of these arid regions are also in tall rocky mountainous regions where the water table is thousands of feet below the surface and digging a well would be impossible even with unlimited funds and resources.
Furthermore (again according to the UN), fully 54% of the world's population live in urban areas. Digging a well in a high-rise apartment or a crowded slum doesn't sound very practical in those locations either, regardless of funds and resources. But even in those difficult locations - there's still fog.
In my initial post I said I intend to develop a water harvesting prototype for irrigation purposes. The reason was simple - if efficiencies of fog harvesting can be pushed to levels economically viable for irrigation, the method would probably also be efficient for drinking, bathing, laundry, etc. when scaled down to smaller size. Condensation itself is basically a small scale event.
Current methods of fog harvesting are admittedly quite inefficient. But then so were photovoltaic cells when they were first introduced. Now we sell our electricity back to the grid and utility companies are scrambling to remain relevant. We didn't stick with the convenient status quo of burning fossil fuels and damming up our rivers.
I opened this thread in good faith expecting to hear honest, thoughtful and creative replies such as those by Mr. Horace (post 44) and Mr. Stewart (post 46). My intent was to gain specialized knowledge…as I am not an engineer myself, but I still get ideas and some of them have proven to be pretty good. At the time of my first post I also had the greatest respect for engineers and the value they add to society, and I would like to continue this discussion in that same spirit.
So here's my suggestion once again in different form: why not heat the intake air to increase the water-carrying capacity, then pressurize it to increase the partial pressure of the water vapor before it reaches the condensor? I called this idea "forcing" the dew point and "doping" the intake air. I simply expected that the experts who work with these physical laws every day would intuitively grasp the concept and advise me if the concept was viable and provide positive guidance. My mistake there - apparently more explanation is needed.

The sketch below should give a rough (and probably imprecise) idea of the concept, including temperature, pressure, humidity, and calculated dewpoint (no I didn't use a table - there's online calculators for dewpoint now). To simplify the collection side of the process, this particular embodiment uses a stone immersed in below grade water to provide constant surface temperature on the condensing element as well as moderate (100,000 gal) storage for the collected water.

I do not consider the energy requirement to be an issue now that solar electricity is cheap and getting dramatically cheaper every year. Moving parts are always an issue and minimizing that factor with passive supplies of heat, cold, and airflow (where possible) are desirable.

I'm also not particularly concerned with the method of collection. Could be a passive net, a nano-fiber towel, a bird beak, a cold stone, a cooling grid the size of a refrigerator, whatever. The recent research is more than convincing that this factor of production is being addressed by some pretty smart people backed by a lot of money and resources. My bet is that collection efficiencies will not be the issue very soon (remember when computer memory was a limiting factor?).

What I am concerned with is the available water in the incoming air. If there's no water in the intake air, the collection efficiency won't matter. I haven't see anyone even trying to look at this aspect of the process. This is NOT a dehumidifier designed to dry out air with water as the waste. It's a water collector with air as the carrier.

Lastly, let's be clear - I'm a confirmed smartass. My skin and my skull are both pretty thick and I really enjoy a good joke (the guys standing on their heads was nice). But please not at the expense of an idea that can potentially be a game changer for large segments of the planet's population in a time of uncertain sustainability and impending climate change.
I invite PWSlack, Mr. Stewart, Mr. Horace, Mr. IQ, and Mr. Mikerho to offer their comments on the validity of the underlying principles of physics in my proposal and my application (or mis-application) of those principles.

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#52

### Re: Water From Air

04/23/2016 7:51 AM

My experience is compressed air purification. In my case water was the main contaminant and we wanted to get rid of it and keep the dry air.

You can use the 'theory' behind the technology but instead keep the water and throw away the air. Except avoid compressors. That would introduce a severe power and mechanical maintenance penalty

There's a 5th way I forgot to mention. There are thermocouple cooling devices that exploit the Peltier effect. None of these devices were viable in my productive years for making purifiers - retired 16 years now. But progress in solar power and thermocouples in terms of availability and reliability - and no doubt price - might open up the potential for water collection in areas with plenty of sunshine and low grade 'undrinkable' water.

You need nothing more than a solar heated cover over the area of water (a black plastic tent). Then with a simple fan to get the moist air moving to blow it through a Peltier grid - and collect the condensate by gravity.

Apart from the fan, it is all achieved by passive elements.

It needs a few electronic experts to make a control method to match thermocouples to solar panels and ambient conditions.

On the other hand, the warm moist air might have a dewpoint high enough to condense in a collector grid (heat exchanger) cooled by nothing more than ambient air. Just another fan needed.

The basic concept seems to be incorporated in your drawing, but I can't make out the precise detail.

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#57

### Re: Water From Air

04/25/2016 10:26 AM

That is why brine ponds are so useful: (1) they hold heat at the bottom due to concentration gradient, (2) they can reach temperatures above the n.b.p. of water at sea level without any means of concentration of light input.

Use a brine pond to preheat the incoming seawater (hopefully without irreparably scaling up the heat exchanger), then spray that water into a chamber to produce saturated water vapor (and vapor only), the chamber will tend to develop a vacuum if the condensation temperature is low enough (and the seawater is degassed somehow prior to evaporation).

As to fog harvesting, one cannot rely upon evaporative cooling processes, since the outside air is already at or near the wet bulb temperature. Thus Peltier cooling or vapor compression cycle (think refrigeration) is necessary for extra yield. If fog already is present more than 50% of the time, then perhaps a mechanical extraction is sufficient to yield useful amounts of water.

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#53

### Re: Water From Air

04/23/2016 10:25 AM

Now this i find odd. You are wanting to utilise the environment to collect water, yet want to over utilise the process by making it power intensive. For the amount of water you will collect, it is far less than the power source you will need to use, so the cost per liter of water will be most expensive to gather and only available at certain times of the day, i.e. night time as the optimal collection times.

In reality, what small scale experiment have you set up to verify the data and your idea, to upscale to a larger system? And what countries are you limiting this too as your idea is sound but not feasible in Africa, unless you are on the Namibian coast line.

"Many of these arid regions are also in tall rocky mountainous regions where the water table is thousands of feet below the surface and digging a well would be impossible even with unlimited funds and resources."

It will still be expensive to locate your equipment to these regions, then to pump it to where you want the water is not cheap either. Great idea you have however, I have doubts about its viability on a larger scale and on its cost effectiveness. No, not convinced yet on your idea! Small scale household maybe.

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#54

### Re: Water From Air

04/24/2016 6:35 PM

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#58

### Re: Water From Air

04/25/2016 10:36 AM

hygroscopic charts - study them intensively.

There are tables that show (somewhere) the quantity of water in 1 scfm of moist, saturated air at various temperatures.

There is also this thing of adiabatic (without heat exchange) compression. If one does that, and it is typical to do, one cannot achieve a high pressure without also resulting in a high temperature. I suppose if you took already moisture laden air (fog), and compressed it, but allowed a slower compression to take place, such that the compression was isothermal (same temperature in and out), some extra moisture could be "milked", but the situation remains centered on how cold the original air is, as to whether this additional work is worth inputting.

Makes more sense to route the fog through some medium so that air temperature is maintained isothermal or slightly cooling, so that minimal losses of condensed water are encountered. I suppose further that engineering could introduce large scale duct work on a mountainside and channel the daily cyclic changes in air density, to help bring cooler air near this project.

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#59

### Re: Water From Air

04/25/2016 1:16 PM

I can only respond to a couple of points you raise. Any psychrometric chart or hygrometer chart will give you the water vapour saturation values. In my line of business I work with grams and cubic metres and degrees C or K, and ISO multiples. As a rule-of-thumb, at normal ambient conditions, it is fairly useful to consider a rise of 11C will double the water vapour holding capacity of air.

I say again, if you have a supply of low grade water and sunshine, you might be lucky enough to get enough potable water using a black plastic sheet stretched over a large area of open water.

The tent heats the air (and maybe the water as well, but it is the air that needs heating). The hot air (warm will do) picks up water vapour. You them move this moist air through a heat exchanger (which needs a means of cooling below the dewpoint of the moist air).

If still in luck, the ambient air might be cold enough to do this. The only power needed is solar panels to drive a couple of fan blowers. One for the moist air and one for the cooler. Or if wind is available then 'funnels' might work. Or if in areas of an excess of labour, then manual pedal or treadle driven fans.

If unlucky, then some form of additional forced cooling will be necessary. This could be Peltier thermocouples driven by solar panels.

I know I am repeating previous ideas - but you must avoid getting involved in unnecessary air compressing and refrigeration, pumping water and heating air and water with elements.

Exploit natural evapouration and ambient air conditions that need just a little bit of help - a nudge in the right direction.

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#60

### Re: Water From Air

04/25/2016 1:36 PM

Sure that works! Brine pond can reach higher efficiency, though. Pump energy becomes low enough to not worry about at some point. Not only that, if the layout is clever enough, who knows? Maybe a large scale thermal siphon could create a natural flow of brine out of and back into the pond, based on thermal density changes.

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#62

### Re: Water From Air

04/25/2016 6:16 PM

Thank You - this is good advice! It's really helpful to know that the effect of a rise in temperature increases the holding capacity that much! I fully agree that exploiting the natural processes passively is a much better way to go. My only difficulty has been knowing where to "nudge" to achieve maximum yield. Both you and Mr. Stewart have been most helpful and given me plenty of material to work on. Please allow a couple of weeks before I post again as I need to digest this new information. Can you point me to a good supplier of instruments? I will need to measure my working models and compare the measurements to performance (water yield) to optimize the system.

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#64

### Re: Water From Air

04/25/2016 6:39 PM

Hello Bruce.

It looks like our comments crossed in the post.

I wish you luck.

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#66

### Re: Water From Air

04/26/2016 9:06 AM

Here's a useful little dewpoint tool I use.

http://cosaxentaur.com/

go to heading 'Service & Support'

click on drop down 'Resource Library'

click on 'Software' under 'Resources' (heading - on right)

It needs a bit of practice.

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#70

### Re: Water From Air

04/26/2016 10:33 AM

"It needs a bit of practice".....I think that could well be said of all of us.

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#68

### Re: Water From Air

04/26/2016 10:29 AM

The instruments you need: a set of kitchen scales, a few gas bags, some tape, some string, and some pipes of various sizes and length. You can bury pipes you need to keep cooler, and expose the pipes (during the day) to add heat to them. If they are rusty brown on the outside or black is not much difference as to absorption of energy from sunlight.

Do not expose the hot pipes to cool breezes, too much condensate loss will take place, and it could interrupt the thermal siphon effect. The larger the duct, the larger air mass transported.

Pay attention to your surroundings, where does dew typically form? Why?

Remember that vapor pressure of water is a property of liquid water, not air. I cannot stress that point home enough.

Catch your warm (or hot) air in a gas bag (try using laundry bags if no Royal Gas Bag is available). seal it with minimal amount of tape, tie if off with string. tape the other end of string to scale pan, and if the bag is lighter than air (have to hurry before it cools) measure the effect by difference from initial weight on the pan (nuts and bolts, whatever). Measure the size of the bad inflated, and get some idea of the volume. Think of it like a hot air balloon where moisture is helping provide lift, but as soon as condensation takes place, the balloon will once again sink (by taking in ordinary air or collapsing). Do some of these simple experiments to get an idea of what makes weather, and make your system become the weather. Find your zen.

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#55

### Re: Water From Air

04/24/2016 6:41 PM

Oh yeah - I'm surprised nobody called me out on the fact that the exhaust air had greater humidity than the intake air! I figured the exhaust air would be driven by the temperature of the big stone, so whatever humidity happened to fall out at 70 deg F was the reality. Maybe not. If so, it might make sense to enclose the system and have it operate at a humidity higher than the surrounding air. The goal is to extract the water. Everything else is variable. Electrical energy is basically free in this concept.

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#65

### Re: Water From Air

04/25/2016 10:18 PM

Oh careful, the "free energy" concept will get you in deep trouble.

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#69

### Re: Water From Air

04/26/2016 10:32 AM

They don't call it Gibbs Free Energy for nothing! Unfortunately, or fortunately depending on point of view, that is always the heat available for mechanical work after the entropy term is subtracted away.

I just want to see "the kid" levitate giant stone blocks using goat skins and steam....or something equally "primitive" but brilliant. I say good luck, let some one else burn castles for a change.

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#71

### Re: Water From Air

04/26/2016 11:23 AM

You're right of course Mr. IdeaSmith - everything requires exchange.

I overstepped there, thanks for bringing me back to being only partially delusional!

What are your thoughts on the basic concept of improving water harvesting yield by increasing the water available in the incoming air to be harvested?

Would leveraging off passive means as much as possible given the particular environment and giving a little "nudge" with the help of (relatively affordable) solar power deliver a theoretically higher yield at the collector end?

I'd like your opinion before I disappear into study for awhile.

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#76

### Re: Water From Air

04/27/2016 5:07 AM

Here is one comment on your idea of heating the air to have more water carrying capacity - it the same as having one litre of water in a 4 litre bucket and then you tip it into a 10 litre bucket. You still have only one litre.

But now you are handling 10 litre containers instead of 4 litre containers. Unless your hot air is allowed to pick up more moisture you are at a loss.

Oh energetically you are at a loss anyway. Trucking the water from somewhere might be more resourceful.

Where is the moisture in the air coming from??? You want to use the water for irrigation? So put it back to the same source where it rightfully came from? Hmm I'd go with the ancient methodology that seems to be field proven. All the machinery will just mean more effort. Sorry your initial question did not bode well and I still think this might as well be a pipe dream.

Given you have not even studied the existing solutions means a lot, don't you think?

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#77

### Re: Water From Air

04/27/2016 12:21 PM

Thanks - that's a good simile. TTFN!

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#72

### Re: Water From Air

04/26/2016 11:37 AM

Of course you are right Mr. Ideasmith - everything requires exchange.

Before I sign off to go study, what are your thoughts?

Will increasing the amount of water in the incoming air improve the yield of the collectors (of whatever type is most appropriate)?

Using passive means as much as possible, then providing a little "nudge" with solar power sounds like the best means to increase the water in the air.

What do you see as the limiting factors to making water extraction feasible on a scalable basis?

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#73

### Re: Water From Air

04/26/2016 11:40 AM

Money, time, energy.

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#56

### Re: Water From Air

04/25/2016 10:18 AM

Bruce: It would serve you very well if you learn one new concept from physical chemistry: "The equilibrium vapor pressure of vapor above a liquid is a property of that liquid and not of the vapor." When one peruses the contents of the Steam Tables, one sees that the temperature of the liquid is given, and the vapor (steam) pressure is a consequence of that temperature.

Rather than heat the air (to arrive at more water vapor content), why not simply intake some water (from the sea), heat that up (through a series of heat exchanges to conserve heat in the situation if that helps), then mist the water through air, or rain it down, but you will also need warm air as you stated, otherwise the condensate will form before you have a chance to effect separation. The air will cool down to an approach temperature to the wet bulb temperature (this is usually a degree or two above the dew point if the temperature is given in Fahrenheit degrees. If Celsius, then 0.5-1 degree. This will typically represent the limit of cooling that can be achieved and maximum conversion of the sensible heat of the water to latent heat of vapor. Elsewhere in your system, you must provide an additional heat exchange between the cold seawater and the warmer saturated or near saturated air, where condensate will be formed.

Your design would by heating the fog, simply take existing condensate micro-droplets, and convert them back to vapor (there is no good reason to do that). To harvest the maximum amount of water from fog, one would need to cool the intake even more, coalesce the micro-droplets by acoustic or other means (such as electrostatics), and then collect as much as will drain off before any subsequent step. A later step might involve chilling the air even further, then impinging this cold air at some velocity "X", on an even colder surface to induce droplets sufficiently large to drain away. This requires some sort of compression/expansion, or a fan (either of which basically imparts energy to the air mass that results in kinetic speed).

Maybe in lieu of all the above arrangement, one could opt for a simple centrifugal effect to separate fog/dew micro-droplets from air. This could be in the form of a giant intake horn facing whatever prevailing wind there is, to channel the flow, increase its speed, and induce g forces within the moving fluid (air/liquid) that will cause the droplets to the periphery. Surely volumes of treatises have already been written on these subjects. Look up such devices as "mist eliminators".

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#61

### Re: Water From Air

04/25/2016 3:50 PM

Thank you James - your advice and guidance is always very helpful and much appreciated and I now have some good direction to study - Steam Tables, Peltier Effect (and also Thompson and Seeburg effect seem to be related).

Just so I'm clear on what you're saying: Step 1 in my proposed process of heating the air to increase the amount of water will not work - rather, cooling the air is a better strategy to achieve that purpose. Is this correct?

Step 2 will work - pushing the air to a cooler surface will condense the water. And adding pressure to the air increases the yield of water condensed. Correct? My understanding was that the surface must be below the dew point of the surrounding air for condensation to occur - Is this also correct?

My main goal at this point is to increase the amount of water in the intake air available

I like your suggestion of taking water from the ocean. My concern would be that water would need to be transported rather than harvested onsite. Transportation is some areas could involve political barriers. Also, would the condensed water be salty?If you could provide some advice also on appropriate instruments to measure temperature, pressure, and humidity at various points of the process I would greatly appreciate it. IQ's suggestion to collect data sounds useful to make improvements and also to collaborate with others in the future.

Thanks again for your patience and all your helpful thoughts! I look forward to continuing this dialog once I have done some more homework and built a few models.

It has never bothered me to launch into a project that I know little about. I have found that if I simply start where I am with the tools I have available, I pick up better tools as I go along and eventually the goal is reached. The only failure is in quitting.

My limiting factors have always been time and energy. I only get so much of these and need to allocate them to the highest and best use (according to my own priority structure). This project seems to have a payback sufficient to warrant the investment.

"In this path of action there is no loss of effort. Nor is there any fear of contrary result." - Bhagavad Gita

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#63

### Re: Water From Air

04/25/2016 6:36 PM

"...Just so I'm clear on what you're saying: Step 1 in my proposed process of heating the air to increase the amount of water will not work -rather, cooling the air is a better strategy to achieve that purpose. Is this correct?....."

Taken at face value, yes! your system might not work, James will have to answer that one - if that is what he said, but I am not commenting on your system.

I am Just making a statement of fact that it is a matter of proven physics that that warm air can hold more water vapour than cold air. You need a means to raise and lower the temperature of the air.

You need a supply of water that can evapourate into the warm air - and that raises the dewpoint..

You then cool the moist air to temperature below the dewpoint and the excess water vapour condenses and drops out. You need a means to collect it.

You will appreciate what is being said when you study the psychometric charts to grasp the basic principles of what you are trying to do.

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#67

### Re: Water From Air

04/26/2016 10:19 AM

I need to clarify a key point: (1) warmer air does have a greater capacity to carry moisture (simply because the vapor pressure of water in contact with that air is higher). Thus one could expose water (by spraying) into warm air, separate any mist droplets that might contain harmful organisms (bacteria, etc.) and solutes (like salt), then the not as warm air (evaporation of some water will lower the actual temperature of said air slightly, or largely depending on how much moisture was already in the air), will be laden with moisture near the saturation point (wet bulb temperature). This air, upon being cooled below the dew point will yield clean, pure condensate (contains very little if any sodium chloride salt or other), that will be suitable for the same use as rain water.

Since highly humid warm air is less dense than dry warm air, and both are less dense than any form of cold air, it should be possible to induce flow inland (if that is what you want), and take off drip condensate if the air loses any heat in transit. At some point inland and at some elevation where the water is needed, apply chilling power and collect a high yield of condensate. The cold air may be conducted back downhill (also in an insulated tube) to assist in setting up thermal siphon flow, thus no fan power is required. It is as a chimney.

Yes you can heat the air (as hot as you wish), and bubble it through water if you wish to load up with moisture. Compression does nothing for you, simply makes the air hotter and a higher pressure, but will not condense out moisture until the air cools slightly. You have to add something to the air, and that something is water that will evaporate in unsaturated hot air. Certainly heating by using a solar field, a brine pond heat source or burning fuel or a nuclear heat source (who wants that much trouble) will allow one to load more water into the air, but it is not going to load itself with something not present at the start, you have to load it.

Several things you probably already know, but don't really think about: (1) steam plumes generally tend to rise in air, (even though you only see the steam when micro-droplets of liquid water are condensing in the cool air around the steam. This has about the same composition as clouds in the sky, and they can reach high altitudes, depending on the energy (heat) input from insolation, etc. (2) Condensate is not particularly salty, but one cannot immediately state that NO salt is present, since instruments exist to test (conductivity) the water condensate down to some extremely low trace levels. A good condensing system should be able to effectively match the qualities of rain water very well, except for the missing nitrogen compounds that result from lightning in the storms.

The only really unique thing about your light bulb moment idea is this: You want to artificially transport water as vapor to some point above sea level and inland some distance. To be successful at all in this, you will need to learn about Dewar flasks.

Basically a Dewar flask is a Thermos bottle, i.e. a container having double walls, a gap between that is evacuated down to very low pressure, and no leaks. If that is not an engineering possibility in nested tubes (for various technical reasons about leakage), then you can mimic this by substituting a high R factor insulation in a thick blanket. The idea is to move the warm air with vapor reasonably quickly, lose the least amount of condensate in transit, and have it arrive where it can be cooled to collect the water. We have already discussed means of cooling, so I should leave it there, but I suspect the most economical will be an ammonia-water cycle that is solar heated to the high upper temperature (generates high pressure ammonia gas), and cooled by ambient air (just like a vapor compression cycle, but you will not use electricity as the driving force)....that is unless electricity is cheaper and highly available at the destination....which I doubt.

Now go forth and prosper, and do this for me: Make a hanging garden palace in the Outback of Australia.

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#74

### Re: Water From Air

04/26/2016 1:16 PM

Thanks James - All I need is a little direction and some honest encouragement and you have given me both! What's your favorite flower? I'll hang it at the entrance to the palace. Gotta go study and experiment - thanks again everyone, TTFN (Ta Ta For Now)

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#75

### Re: Water From Air

04/26/2016 2:19 PM

That is easy! The Yellow Rose of Texas! Favorite all-time song too! That or "Under the Bower" - it was the song the Army of the Republic of Texas played while marching on Santa Ana at the Battle of San Jacinto.

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#78

### Re: Water From Air

04/27/2016 1:07 PM

Well, I have been lured out of the shadows! I am a sorta retired environmental (degreed as chemical) engineer with many years experience in the power industry. I was often tagged to review ideas that came from the general public regarding ways to improve one aspect or other of our operations. Part of my assignment was water resource management, since our steam/electric generation facilities are all in "semi-arid" locations, often utilizing either city effluent (treated sewage) or well water in mind boggling (to those not acquainted with water usage) volumes. Additionally, I grew up on and manage operations now of several "semi-irrigated" farm operations in the same semi-arid locations.

One of the problems I so often dealt with in suggestions of how to solve one or other problem at our facilities was the willingness of "idea persons" to either ignore, or fail to understand the basic laws of physics: to wit, the thermodynamics in this case of transforming water vapor (a gas) to liquid water, and the enormous volumes of water required in irrigation.

The heat demand, regardless of novel approach, to convert a pound of water vapor to liquid water without a change in temperature is about 1000 Btu's / lb. Compressing air, cooling air, or any other magic approach will still add energy demands. You just can't get around it. You might be able to use wind or solar to accomplish this, but the installation, operation, and maintenance of even these "free" sources of energy are going to be real.

The volume of water for irrigation in an arid climate will, of course, vary with the available rainfall (or dew, which is that same once it gets into the soil, as rain), the evapo-transpiration demand of crops, and the efficiency of the irrigation system (can the water be deliverd directly to the roots of the crops without percolating past the roots, etc.

Assume that you have a crop that will need about 20 inches of rain for a growing season (that is for cotton grown in my area). Assume again that you get half of it from rain, or 10 inches, so you need 10 inches of water. The volume of water, with very efficient irrigation delivery (if you let it run down a ditch to the crops, it will be lost to the soil), that will amount to about 27,000 gallons per inch per acre (about 206 feet by 2006 feet), or 270,000 gallons of water. That will weigh about 1.8 million pounds, and demand 1,800,000,000 Btu's to convert vapor to liquid.

Of course, you will have to find some form of storage in order to manage the water. Assume a small third world type farming operation, you would likely need several acres per person per year, and so many people per village, and you begin to see the enormity of "terra-forming" a third world village. So to store just a couple of weeks water for demand storage, and you will need a sealed (don't forget the evaporation rate from a water surface that can easily exceed an inch a day in high heat and windy conditions, when the humidity is low!) containment.

But, we never let physics slow us down, now, do we?

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#79

### Re: Water From Air

04/27/2016 2:30 PM

Appraising others people's ideas to see if they would work! - nice one - old habits die hard!

Now you have popped in to go through the suggestions offered you end on a negative note to suggest we shouldn't bother.

The OP wanted to know if water can be made from air - not how to transport it.

Whilst your helpful input introduces some factors to assess the scale of the operation he still has to 'make' the water in the first place - so what is your answer to his problem - on the scale you envisage.

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#80

### Re: Water From Air

04/27/2016 2:36 PM

Nature does it all the time, many places, just not where we would like it to appear.

Yes, they either have to have a huge impoundment for water requirements that large, or be ready to use the water on a continuous basis.

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#82

### Re: Water From Air

04/27/2016 6:53 PM

Wow - Nicely said Mr. Huntsman10! This morning I was prepared to exit to my own devices but you brought me back to this conversation as well.

And you're right, I simply refuse to allow the existing understanding of physics to deter me from accomplishing a goal I believe is important. It's just that our current understanding of physics keeps changing. Things we were absolutely sure were impossible 15 years ago are now commonplace (I won't bore you with a list - you all work with advances in technology every day). And yet we still remain sure that what's impossible today will remain impossible tomorrow.

It's called the Black Swan effect - for centuries people were certain that it was genetically impossible for such a creature as a Black Swan...Until somebody found one. Then the body of wisdom was quickly re-written to teach that "Of course, we knew that all along. "Ex Ante Impossibile, Ex Post Patet! Every major scientific advance across the course of history has followed this pattern. I see no reason to believe this case is an exception.

I'm sorry some on this post seem offended by my apparent lack of "research". I'm doing research right now by asking questions!! Those of you who were there may remember Tim Berners-Lee's comments on his intent behind developing the first web protocol - to allow free collaboration and exchange of ideas in order to speed up discovery and progress. Sadly you won't find that comment anywhere in the official history of the internet. My previous searches on harvesting water from air reached a dead end and I needed new directions to search. Now I have them. Besides it's very entertaining to hear some of the comments.

I grew up in a scientific community with 4 Journals on our coffee table - Science, Nature, JAMA and Architectural Digest. Starting at age 11, I read every issue from 1970 through 1990. I often didn't understand the exact language but the progression of ideas was stunning! I currently hold a Doctorate Degree as well as an MBA in finance, I've spent several years training new grads to high levels of success in my field of expertise and I'm now again a full-time practicing clinician in the #1 Job in America (according to US News and World Report, 2015). I am definitely not a member of the "drag and drop" generation but I do consider it a compliment that some consider my questions to be so naive that they think I am of tender years.

The region where I live - Inland North San Diego County - is mostly avocado groves and "waterwise" California Natives. It's considered a Coastal Desert climate with a wide range of subclimates. I'm fortunate to have at least 4 of those subclimates on my property as well as a fog that marches 20 miles up a river valley from the coast . I'm very familiar the watering requirements of agriculture and in fact many old groves are being cut down because the price of water has been artificially inflated. Water shortages and drought in Southern California are common. I don't have any real yet answers but I do see a pressing need locally and one that appears to be growing globally. It doesn't seem intelligent to wait for a crisis before we act.

You may think I'm a quack or a fool and that's OK. But please keep telling me - as precisely and as specifically as possible - why this can't be done. What are the obstacles - exactly? You may not realize it but you are defining a "roadmap to the moon". It may not happen in the next 100 days or even in our lifetimes, but it seems like a thing well worth applying time, energy, and those most important ingredients - attention, imagination, and persistence. I intend to contribute whatever resources I can and hopefully collaborate with others of similar mind.

Thanks again everyone - I've received much more good information and solid advice than I expected at the original post.

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#83

### Re: Water From Air

04/27/2016 7:56 PM

I never said it cannot be done. Read my comment below. It is done every day. I only state that your approach is focused on using thermal and/or compressive energy. Results can be predicted using those means. And, let's face it, your question was about that!

I would love a list of basic thermodynamic principles which have been debunked in the last 15 years (which would really affect me since I haven't been in a basic undergraduate physics class since Nixon was in office! I do, however keep up with my engineering journals.) So bore me! Most of the change in physics understanding are deeply in the quantum mechanics field. I would not consider things like the confirmation of gravitational waves or the existence of Lagrangian partials in orbital perturbations the same as upsetting the laws of thermodynamics.

However, I well remember as a child seeing the lovely volumes on "Natural Science" (a term that does date me (carbon date me?)) full of speculation on current understanding that became laughable in short order.

Many things in "scientific understanding" are fluid. As a result, I suspect that biology is more religion than science (considering a denial of the existence of a spiritual or mystic influence is by definition a held belief, but I digress, once again).

To your example, predicting the breeding probability for black swans, in an era long before Watson and Crick explained and identified the complexity of the spiral helix of basic genetics is hardly analogous to a process that is so easily and frequently observed and defined. I would have to say that, as long as we are dealing with a system not noticeably affected by the extremes in Einstain's relativistic principles, we are usually able to clearly predict physical probability using only Newton's principles and a Cartesian set of measurements.

But, to date, and staying on top of the topic of basic physics, I see little change in the observed and documented principles of thermodynamics, which is pertinent to your initial postulate. As I said, it often is accomplished in so many ways. I am saying that scale and energy requirements are prohibitive with current technology and resources, given the parameters of your conundrum.

Progress using a process of simple condensation, is likely to be limited to incremental improvements in efficiency (even with a 100% efficient refrigeration system which is so impossible under the accepted engineering principles of a heat cycle, which you are willing to ignore for progress) or some form "free power" (again, a leap of faith for the practicalist). Your initial postulation is for a purely thermodynamic conversion of gas to liquid.

My suggestion, if you are looking for a positive spin, is for you to seek to sidestep the thermodynamic hurdles with hygroscopic (or call it hydrophillic) systems that absorb water from the air rather than "forcing dewpoint" and then can be convinced efficiently to release the water as needed. Presently, most such materials will need to be heated, and the water condensed as it is released, leaving you with another thermodynamic hurdle. Unless you can fix that one. There is your challenge!

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#87

### Re: Water From Air

04/28/2016 10:18 AM

Once again, spot on. Not only does thermodynamics tell us it is either possible or impossible (to occur in a spontaneous, energy releasing way), but it can never state how slow or fast that process might take place (unless we get off into attempting to tie an "activation energy" on every physical process as well as the chemical ones.).

Generally speaking - more area is conducive to a kinetic process than less area. More heat will enhance a process better (rate wise) than less heat. Higher thermal coefficient of performance is always better than lower when it comes to chilling a process.

Nature has examples of what seems to work for her, and what does not. (cactus needles are just one example).

I could imagine a condensing chamber where instead of a "spherical" or tubular heat exchanger surface, one might find a few "arms of cactus" with "needles" made of a highly conductive metal (aluminum, maybe copper or silver if money were no object). Even if it did work better than a more traditional heat exchanger (which it might not), can anyone afford to make it or own it?

Heck, a Lithium bromide absorbing system from Siemens Energy might be just his ticket.

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#97

### Re: Water From Air

05/16/2016 5:40 AM

My two cents.

You will find a lot of people with similar mind, but you will not get around the laws of thermo-physics.

What unit is used for the dew point should be a dead give-away for the forcing.

Everything else has been said. Good luck in your research.

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#81

### Re: Water From Air

04/27/2016 3:51 PM

RE: Horace40. Of course the short answer is, as Mr. Stewart observed, of course you can do it. Nature does it all the time. And as he also observed, not where we would like to see it.

My own personal first principle of engineering is, "If you wanna pay for it, we can do it!" So how much do you want to pay? Is it worth the trip? Does it waste resources?

Anyone who has sat in a restaurant, with a humid enough atmosphere, with a glass of iced water on his table, whether that person was aware of it or not, "harvested water" from air. I do it all the time with my trumpet, as well (we call 'em "spit valves", but it SHOULD mostly be condensate) except the time I played an outdoor concert in Lubbock, TX when it was over 105 degrees and the relative humidity was in the single digits! That was one dry concert, no spit, no drip. Too high an energy cost in that case, to be practical!

Another of my power plant duties was to check compressed air lines for condensate (not the same as the steam condensers, as discussed above) to protect the equipment which depended on available high pressure air, so compressing air can make the dew point rise while the air is under compression (it goes right back when you release the pressure), but the thermodynamic cost remains, but the means is less efficient than simple refrigeration. I digress.

I apologize if stating the obvious is such a downer. If you want to spend a couple thousand Btus for a glass of water, it is for you to decide the acceptable rate of return.

The OP asks, "Is there any way to force dew point?" The entire thread, from my view, dances around the point that dewpoint is a multi-variant number, predictably dependent on temperature, pressure, and (perhaps, but not likely pertinent to this discussion) variable chemistry of the gas. That is the price of thermodynamic change. No magic, no shortcuts. In order to bring water from a gaseous state to a liquid state, or reverse, there is a thermodynamic cost, which is NOT path dependent.

Certainly the possibility exists that a better way, perhaps a more efficient heat transfer method, can be found, certainly, but the basic cost remains. Efficiency of operation will come with harnessing more efficient ways of generating the energy or transfer of energy from one type (for example, solar energy photons to electric current) to another (creating a heat "sink", such as refrigeration, or bimetallic heat change). The same with pressure change, it takes horsepower.

As to the volumes required for a reasonable irrigation project, I see it as the same. I can keep my flower pot growing with a glass of ice dripping condensate into the soil. Would it be more expedient to melt the ice and put it on the flowers? Is it a matter of just scaling up for practical reasons? That is reality.

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#85

### Re: Water From Air

04/27/2016 9:31 PM

That is a very interesting reply. I appreciate your efforts in this. There is a 'cost' of course - but not necessarily equated to money. And does it matter if there is an endless supply of the means to pay. It comes down to the resources available that you have to make it work.

I know I am being silly if I said the cost could be a cup of sand in return for a cup of water. Someone in the parched desert might not worry about the 'cost' of an inefficient system. Whereas someone in the Antarctic might not be too keen on doing business with you.

To move forward, I think the water extraction system needs to be based on what energy resources are readily available. To my mind, that means solar power for heating passive devices, and making electricity to drive Peltier devices or fans.

A temperature-swing in fact.

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#89

### Re: Water From Air

04/30/2016 8:25 PM

Well, believe it or not, here is a shot of an old homestead where I was trying to replace a vegetative cover 4 years ago, in the height of the Texas drought. We had about 2 inches of rain spread out over 16 months before this.

That might have sounded like a good deal back then, an equal volume of sand for water.... And if you're just thirsty, it is. But irrigation comes at a cost most people just can't fathom. We would have needed 20 inches of rain to make a full crop that year. 20 inches of topsoil traded for that rain would have left the farm unable to grow anything after that, there would only be unusable clay and caliche' left!

Strangely enough, though, the noxious weeds (mostly tumbleweeds, more properly, Russian thistle, the cost of having planted Hard Red Winter wheat from Siberian stock) thrived just beyond where this shot was taken.

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#90

### Re: Water From Air

05/01/2016 6:52 AM

Thanks for the insight to farming in drought times in arid lands. I have no idea of how much water is needed for growing things outdoors but I do know about looking after an indoor cactus in a flower pot. I suppose it is not surprising the cactus can go a long time without regular water but it gradually shrinks. I have another flower (a wildflower - I don't know it's name - but I think it might be sorrel) that acts an an indicator. It shows distress after only a few days of dryness.

I have to accept your comment about trading your topsoil for water being a non-runner -but in defence of my logic that you barter with something in endless supply - my 'sand' example does not apply in your case. What do you have to trade with???

But on a technical point - would your drought problem be solved (partly) by methods to conserve the little water you do have - to use it more efficiently. And even if there was a 'magic' system to make water from air to irrigate your crops - you would need an equal area of 20" of water elsewhere as a source.

Personally, I cannot hope to suggest a real solution because I do not know anything about the logistics and costs of survival in an area like yours.

My initial guess is you would need to rely on solar power (or windmills?) to devise a means of cooling what air you do have to below dewpoint and collecting the condensate - and then distributing it to your plants. The air will cool naturally at night so the dewpoint rises meaning less demand on you chilling device - but probably needs batteries to store power during the day from solar panels.

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#94

### Re: Water From Air

05/02/2016 8:24 AM

I am saying this can be done in a completely passive way, but it does require the moisture carrying air mass to be as hot as possible up to the normal boiling point at sea level. In that way, ambient air will be sufficient for cooling, and also if passive still not good enough, thermally driven refrigeration such as ammonia cycle is far more energy efficient than any reported Peltier effect cooler.

No pressure swing is needed on the air mass, although it would allow even higher temperatures and obviously more moisture carrying capacity.

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#86

### Re: Water From Air

04/28/2016 9:23 AM

Well put in both posts, kudos. I guess you were glad to have Lubbock in your rear view mirror, as am I at times (mainly when the sky is red with sand), but I live here, so I keep coming back for another dose.

Pointing out that the result of thermodynamics is clearly not path dependent was a master stroke, and something that always needs to be pointed out, or brought in as a reminder. That should be instructive to those wishing to "cheat Mother Nature".

IF "we" could engineer a power plant (and make it work) with mud fence left-overs, that well we would do, since it would be dirt cheap. Unfortunately, the idea just won't hold water, so we upgrade to various other metals, concrete, ceramics, polymer insulation, and a host of other materials.

Never mind that it mostly started out as rock, mud, and petroleum out back there somewhere. That is not ignoring physics, just transforming nature around us into a format most useful and expedient -- at a cost.

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#88

### Re: Water From Air

04/28/2016 10:33 AM

Mr. Stewart:

Lubbock is, in fact, in my windshield this evening, and only in my rear view mirror for a short drive thereafter! I am not far from there, just 28 miles to the SW! Yes, it is a harsh place to live, but that keeps out the insincere pretenders!

Being reared in the arts of putting trash into service, I would probably be the first to jump in line to help scotch together a power plant from whatever was lying around, but with a clear eye to the costs and likely results! I spent enough time on tractors gleaned from the last pile of junk at the farm auctions in my early years!

Good to know I'm not alone here in the high plains!

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#91

### Re: Water From Air

05/01/2016 1:30 PM

I'm sorry to hear about your land in Texas - losing everything is never fun. If you can clarify please because I'm confused by your statement: "In order to bring water from a gaseous state to a liquid state, or reverse, there is a thermodynamic cost, which is NOT path dependent." Mu understanding is that condensation is an exothermic event - wouldn't energy be thrown off by the process? BTW - Watson and Crick announced the double helix in 1953. The first Black Swan was identified and reported in 1697 by Dutch explorer Willem Vlamingh in Western Australia, over 250 years earlier. The Black Swan myth was debunked long before Watson and Crick, who did not identify Basic Genetics. That description was originally by Austrian Monk Gregor Mendel in the late 1800s. And the "Laws" of thermodynamics themselves didn't even begin to exist as a formal theory until Thompson and Carnot in the early 1800s. The point is that we always think it's unreasonable before the fact (Ex Ante Impossible!). We always think it's obvious after the fact (Ex Post Patet!). As humans, we are "Always Right". Even when we learn we are wrong, we are right that we were wrong! It's a difficult reality to accept. Avocados require approximately 800,000 gallons of water per acre per year. My area averages about 14 inches of annual rainfall. Not nearly enough, even in an El Nino year. But soil conditions and mild climate make for an ideal situation if water can be delivered, and the market is very close. Ripe avocados don't transport well. I agree that sidestepping the thermodynamics is the way to gather the water. Maybe nanotubes or a catalyst or bird beaks or most likely some method that has not yet been suggested. Who knows when, but it's coming. My concern (to Mr. Ideasmith's point) is that once we learn how to harvest the water at a high rate, the surrounding air will be relatively water barren. Maybe only for an instant, but new air-rich water can only move in at a limited rate. Take that idea far enough and fast enough and you will run out of incoming water. There must be a way to "push" the system. Solar looks like the most promising source of energy for that push. Or maybe the conditions today aren't favorable to passively harvest. On your property in Texas during those days without rain, there was probably a lot of energy from the sun hitting the surface. Probably more energy than you wanted. There may have also been times when RH was high. Possibly even uncomfortable humid. Wouldn't it have been handy to convert that excess energy (via a means) to available water? Maybe only in small amounts gathered consistently over long periods of time and stored until needed. When the rain did come, was it harvested and stored?

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#92

### Re: Water From Air

05/01/2016 6:24 PM

Land has healed somewhat. Normal drought/rain cycles take care of these things. We are still back in a little drought, not nearly as bad as it was. Several hundred miles to the southeast (actually, about 700 miles southeast), still in Texas, they are receiving more water than they can handle. Micro climates!

You are correct, condensation is exothermic, so the Btus from condensation must be removed, or the condensation stops. Natural convection takes care of that on a climatic scale. But you have asked for come kind of powered cycle requiring the forced removal by energy exchange (refrigeration cycle for example). In nature, as air is heated up, it expands (thermal expansion), becoming lighter per cubic foot, and rises. As it rises, it goes higher, and as it gets higher, the ambient pressure drops, since there is less of the atmosphere pressing down on it. Expanding gases cool (and compressing gases heat, which is why it is cooler at the top of the mountain, usually). Then, the air expands more (PV=nRT), eventually, potentially, dropping below the dew point (which is a function of weight of water per weight of gas). When it drops below the dew point, droplets form, making what we call clouds, and MIGHT begin to gather up to make rain. If the air cools to the same temperature as the surrounding air, but remains below the dew point for those conditions, it stops rising, and eventually cools and circulates down. This is adiabatic turndown; the natural rain cycle.

Normally, during the day, if it happens to be in an area in which the vegetation is lush enough to transpire sufficient moisture, or there is available surface water, (or, you have a neighbor who is burning hydrocarbon fuel in his boiler), the dew point of the air near the surface (troposphere) will actually be elevated. Then, when the earth cools at night, perhaps the air near the surface may reach the dew point, and get dew, or perhaps fog. For this reason, the exothermic release of energy as water condenses to fog or dew will keep the air temperature at or above the dew point.

You have just told us that the water demand for your trees is 800,000 gallons per year. 800,000 gallons divided by (7.4805 gallons per cubic foot times 43,560 square feet per acre divided by 12 inches per foot) means you need 29.46 inches of irrigation plus precipitated water. Since your rainfall (assuming it falls when the trees need it!) is 14 inches, your deficit irrigation demand is 15.5 inches per year, or 420,890 gallons per year. I assume trees do most of their growth in the later spring and summer months, at least due (not dew) to the longer daylight and one must assume warmer temperatures. (Yes, I have designed and permitted several wastewater irrigation disposal systems in my time!)

Dusting off my 35 year old psychrometeric charts (these haven't change in the last few years, I assume), I see that at a dry bulb temperature of 65 degree F and a relative humidity of, say 70%, there are 0.0095 pounds of water per pound of air. Since air has a density of 0.0074 lb/ft^3 at 65 degrees, the available moisture is 0.0000703 pounds of water per cubic foot. The enthalpy of air under these conditions is 23 Btu/lb air at saturation (dew point) and the dew point is 56 degrees.

So, in order to remove some of the moisture (getting it all would be VERY inefficient, as heat transfer gets really difficult at temperatures well below ambient) we will need to subcool it below the 55 degree dew point. If we were to be able to subcool the air to, say 25 degrees F, the water content would be 0.003 pounds per pound of air, and we would have harvested .0065 pounds of water per pound of dry air. The enthaply at that temperature is 9 Btu/lb. air. So we subcooled (1/.0074= 135) cubic feet of air 40 degrees F to harvest 0.0065 pounds of water at a cost of rejecting (23-9) 14 Btu's. Since water weighs 8.31 pounds per gallon, we will need to process (8.31/0.0065 x 135) about 172,000 cubic feet of air! At relatively high humidity. And we had to reject about 18,000 Btu's.

Assuming your irrigation season is about 4 months long, that comes out to about 3,500 gallons a day. If you can run the system about 6 hours, you will need to produce 584 gallons per hour, or 9.7 gallons a minute. You will need a throughput of (hold on to your socks) 1,800,000 cfm......... I don't know anything short of a set of power plant induction draft fans, which use in the 5000 horsepower range that can do it. For one acre. The cooling surfaces alone will be enormous.

Well, you dragged it out of me. There's the science and engineering principles.

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#93

### Re: Water From Air

05/01/2016 9:41 PM

Thank You Mr. Huntman10 - this is the solid answer I was hoping for in my original post - you are truly an engineer! It never occurred to me that the Btus from the condensation must be removed or the process stops - again thank you for pointing out that failure path. Now I can see how big the obstacles are that must be overcome and can begin to identify solutions. I can't say that I fully understand all you said, but I will study your words and learn. This method always works. I would hope to consider you my friend moving forward. I certainly owe you one (or two) for your analysis and this education. Please let's stay in touch and if you ever happen to find yourself in South Cally please look me up - I'm not hard to find. And also to you Mr. Stewart - Your leadership has been much appreciated in this conversation! I hope to meet you both in person someday. You sound like decent people.

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#95

### Re: Water From Air

05/02/2016 8:57 AM

We used to have this thing here at the local University (Texas Tech University) called ICASALS

which is the International Center for Arid and Semiarid Land Studies. Maybe we could get them to host a conference on this very topic, and we can chew and eschew it, until at least a drop of dew forms on our iced tea (or adult beverage) glasses.

I think what everyone seems to be missing is: Artificially drive (although still passively so it could be done on a "massive" scale.) the process of saturating warmed to quite hot air by undesirable irrigation water (seawater, some nasty wastewater, etc. too saline, too brackish) some distance away from where the irrigation project will be.

Since the area to be irrigated is be definition semi-arid to arid, consider using some form of concentrated solar energy (\$\$\$), or a solar chimney (\$\$\$\$), to produce any needed electric power (nuclear power is also fine by me). With sufficient nuclear power plants lined up, it is possible to lift the excess water from flooded areas of Texas, or the upper Mississippi River basin to West Texas. OR we could fire the EPA, and tell Denver to start shipping waste water downhill to West Texas, or else be invaded. (We sent a wave of Texans to Colorado before, don't you folks remember that disaster? LOL) Now one has all this large air mass in a large duct flowing uphill (the source has to be downhill in this example, but it is possible to irrigate the lowest point on earth the same way as long as the condensation takes place up high somewhere on a mountain), since you used a brine pond to heat up the system (incoming water and air) to a point where you effectively have 2 bara pressure simply by heating air and water and intimately mixing (yes you must provide some pumping energy Mildred), it will take less to "wring out the cloth" at the end of pipe where harvesting will take place. In fact, if the air can be kept hot enough, one could even drive an Organic Rankine Cycle plant to (1) generate needed electricity, and (2)provide a cold outlet temperature from the turbine, depending on choice of working fluid.

Do not overlook the positive effects of skirted solar chimneys. These can actually make the skirted (tented) area which is large operate with far less evaporation losses than the land around it, effectively can make its own weather inside, and who knows what mankind will develop in the future (stabilized atmospheric vortex cooling towers actually enhance local rainfall). There is always an excellent answer, always more than one good answer, and always a common denominator \$\$\$ for both. Mankind needs to be finding more reasons to stop killing each other in the name of religion, and get on with loving each other in the name of religion, and finding ways to help each other survive, let the planet take care of the killing, she is expert at it.

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Location: Wales, UK
Posts: 348
#98

### Re: Water From Air

05/18/2016 11:48 AM

Re your personal first principle of engineering "If you wanna pay for it, we can do it!"

A customer of mine, (special purpose design), had a saying, when asked if it could be done, would say, "If we can put men on the moon we can do anything but have you got NASA's budget".

Best regards,

John.

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Best advice I can give as you get older "Never miss an opportunity to relieve yourself"
Guru

Join Date: May 2009
Location: Richland, WA, USA
Posts: 20033
#84

### Re: Water From Air

04/27/2016 8:09 PM

Whatever system you build, or even just conceive, is strictly limited by the flow of air and its moisture content that can be made to transit the system.

Heating the air makes it capable of absorbing more moisture, but if there is no more ambient moisture to be absorbed in the first place, the air won't actually absorb any more.

Think turnip and blood.

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Guru

Join Date: Jan 2006
Location: Tamworth, UK.
Posts: 1551
#96

### Re: Water From Air

05/02/2016 9:16 AM

You have had some useful advice by James and having dismissed a workable Peltier method, offers an alternative, but efficiency is not the issue at the moment, you want something that actually works on any scale.

Then you can tune to efficiency when you scale it up.

But whatever method you use, where do you expect to get all the energy/power from to drive these alternation devices. Efficiency is not just the chiller, but the overall power generation, air movement, condensate collection, water distribution and on-going maintenance.

I wish you all success.

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