Pulling water from the atmosphere

[Ctingle30]

Hello. I'm playing around with the concept of air wells. I recently came across some information on rock piles that were built in ancient Greece to pull water out of the air via condensation that occurs in the cool center of the rock pile (60 feet in diameter and 30 feet tall). Can anyone help me figure out how to calculate the amount of water that could potentially be captured in a system like this? If you search for "Zibold Condenser" you'll get an idea of what I'm talking about.

Mahalo,

Chris

[Sensei]

Quote

Pulling water from the atmosphere

It can be done using airplanes which are spreading silver iodide or dry ice etc.

https://en.wikipedia.org/wiki/Cloud_seeding

57 minutes ago, Ctingle30 said:

Can anyone help me figure out how to calculate the amount of water that could potentially be captured in a system like this?

I think it depends on humidity of air.

 

Edited November 21, 2019 by Sensei

[J.C.MacSwell]

If you assumed a temperature and relative humidity of the air that would give you the dew point. The rocks would need to stay below that temperature, so you would need to know their starting temperature, mass and specific heat. The humidity in the air would of course drop from the condensation. and that of the rocks increase. You could do a calculation based on the rocks getting to the dew point temperature to get the "potential" but the airflow and surface area of the rocks would affect how long things would take to get an amount less than that.

[Ctingle30]

Thanks.  If I built a chamber in the middle of the pile and placed evaporative coolers (large unglazed pot with smaller unglazed clay pot inside it and wet sand in between them) so that the core stayed around 60 degrees and ventilated the pile with PVC coming in from the sides and out the top...would the continuous moist airflow coming into the pile keep the condensation going or would it cycle from night (cold center) to day (not as cold)?

My thanks,

Chris 

[J.C.MacSwell]

21 hours ago, Ctingle30 said:

Thanks.  If I built a chamber in the middle of the pile and placed evaporative coolers (large unglazed pot with smaller unglazed clay pot inside it and wet sand in between them) so that the core stayed around 60 degrees and ventilated the pile with PVC coming in from the sides and out the top...would the continuous moist airflow coming into the pile keep the condensation going or would it cycle from night (cold center) to day (not as cold)?

My thanks,

Chris 

You want to use evaporative cooling to provide the heat sink for condensation?

To the degree you do that you won't break even.

[Ctingle30]

I was thinking the warm outside air would condense when it passed through the cool center of the pile. No?

[mistermack]

I have an engineer friend who used to work in Saudi Arabia. He says that at certain times over there, condensation would be streaming off the metal roofs of the modern industrial buildings and running down the downpipes from the gutters as if it was raining. I doubt if it would last for long though. The condensation would be bound to warm the metal up past the dew point very rapidly. 

You would need a combination of very clear skies, and high humidity, to maximise the yield. I'm sure it's been tried over there. If he noticed it, lots of other people would too. 

I prefer the transpiration bag idea. So long as there are some non-poisonous bushes within range, you can get a lot of water using a few plastic bags, and the local bushes. They suck up the water from below, and deliver it at no cost, other than the effort of collecting it and resetting the bag. 

 

[J.C.MacSwell]

46 minutes ago, Ctingle30 said:

I was thinking the warm outside air would condense when it passed through the cool center of the pile. No?

Sure. But any augmentation of the cooling by evaporative cooling, on its' own, will use at least as much water as it will increase the condensation unless you have some other source of drier and cooler air, some other heat sink below the temperature of the rocks, or some other refrigeration cycle, all of which could be done more directly unless I am missing something.

The main benefit of the rocks would be from nocturnal cooling and diurnal water harvesting by condensation...a concentrated version of dew on the grass in the morning.

 

6 minutes ago, mistermack said:

I have an engineer friend who used to work in Saudi Arabia. He says that at certain times over there, condensation would be streaming off the metal roofs of the modern industrial buildings and running down the downpipes from the gutters as if it was raining. I doubt if it would last for long though. The condensation would be bound to warm the metal up past the dew point very rapidly. 

I've seen this effect inside sea cans that have been opened up on foggy mornings after cooling overnight (or if snow on the roof)...literally raining inside the containers as the roof is flat. Only on (somewhat) rare conditions, but it can get pretty wet inside.

[mistermack]

One thing I dreamed up, a few years ago, was a possible way to green some of the world's deserts. I don't know if it would work, it would take some serious political will to embark on. 

The idea is that you start with a desert or semi desert close to the coast. It has to have a history of regular onshore winds. What you do is to install some serious seawater pumps, a few hundred metres from the shore. When there is any significant onshore wind, you pump seawater upwards, in an extremely fine spray, so that the water evaporates, and the salt falls back into the ocean.

The humid air travels inland, where it is forced upwards, forming clouds and giving rain. The combination of clouds and rain transform the barren land into rich agricultural land, taxes on which pays for the pumping operation. In time you might even get rivers to flow, enabling secondary irrigation using the same water. 

If the economics don't add up now, they might in the future, if there is cheap electricity from fusion reactors. 

Somewhere like the Nullarbor Plain in Australia could be transformed into a real bread basket, with regular rainfall. And all you need is an onshore wind, and the money to operate the pumps.

[Sensei]

10 hours ago, mistermack said:

One thing I dreamed up, a few years ago, was a possible way to green some of the world's deserts. I don't know if it would work, it would take some serious political will to embark on. 

The idea is that you start with a desert or semi desert close to the coast. It has to have a history of regular onshore winds. What you do is to install some serious seawater pumps, a few hundred metres from the shore. When there is any significant onshore wind, you pump seawater upwards, in an extremely fine spray, so that the water evaporates, and the salt falls back into the ocean.

The humid air travels inland, where it is forced upwards, forming clouds and giving rain. The combination of clouds and rain transform the barren land into rich agricultural land, taxes on which pays for the pumping operation. In time you might even get rivers to flow, enabling secondary irrigation using the same water. 

If the economics don't add up now, they might in the future, if there is cheap electricity from fusion reactors. 

Somewhere like the Nullarbor Plain in Australia could be transformed into a real bread basket, with regular rainfall. And all you need is an onshore wind, and the money to operate the pumps.

The problem with desert is that it has no significant amount of soil which is basically centuries and millennia of dead plants (natural compost). New plants to grow need nutrients. Where are these nutrients? In soil. Gathered from rain, and produced by other living organisms like bacteria and fungi. Water from rain quickly passes through sand, but it last longer in soil. During stormy weather there are thunders. They make NOx compounds, which fall with rain to soil. Plants need Nitrogen to grow. Without Nitrogen they won't be able to grow. It's often the case in plants growing in human apartment. They don't have access to rain, so after months and years soil is exhausted from Nitrogen compounds. I am catching rain on balcony and giving it to my plants. Alternative is to use artificial fertilizers.

[mistermack]

30 minutes ago, Sensei said:

The problem with desert is that it has no significant amount of soil which is basically centuries and millennia of dead plants (natural compost). New plants to grow need nutrients. Where are these nutrients? In soil. Gathered from rain, and produced by other living organisms like bacteria and fungi. Water from rain quickly passes through sand, but it last longer in soil. During stormy weather there are thunders. They make NOx compounds, which fall with rain to soil. Plants need Nitrogen to grow. Without Nitrogen they won't be able to grow. It's often the case in plants growing in human apartment. They don't have access to rain, so after months and years soil is exhausted from Nitrogen compounds. I am catching rain on balcony and giving it to my plants. Alternative is to use artificial fertilizers.

That's all true, but deserts can be farmed very profitably if the water is available. Israel is one of the world leaders, they have huge areas of desert growing stuff like Jojoba. If you have a water supply that isn't going to run out, you can build up a soil over the years, growing crops initially that are suited to more sparse conditions. Some crops, like Clover, fix nitrogen from the air in their roots, and improve the soil as they grow.

There's loads of stuff on youtube about growing crops on desert soils. 

Edit : More directly relevant to the OP, this youtube video shows Israelis extracting dew from the air, using plastic around the roots of each plant. It starts at 3:10 

 

 

Edited November 23, 2019 by mistermack

[J.C.MacSwell]

Nice video Mistermack.