Okay engineers, tell me what you think. (environmental magic, or more hype?)

Water seer ^ | unk/recent | website

[Garth Tater]

Please stop with your blanket statements. Where was it shown that this device doesn't work? Shown to not work everywhere? People have been using less efficient devices than this one to condense water from the air for thousands of years.

Does this device give you 37 liters per day of condensate every where and all the time? Unlikely. Does it condense water from the air in many places. Very likely. Blanket statements that include "show-stopper" don't really address the usefulness of this device to some people.

As shown, it just doesn't have it, even if all of the other factors you describe were ideal.
Surface area of the earth in contact with the device ...THIS is the show-stopper.

The conductivity of the surrounding earth can differ by an order of magnitude depending on its moisture content. Are you sure that you know there is insufficient surface area of the earth in contact with this device in all locations it may be used? Thanks for the conversation but I'm not interested in discussing your show-stopping facts anymore.

[kosciusko51]

I'm not trying to dismiss this system; I am saying it won't work "as advertised."

It will not meet it's advertised maximum rate of 37 liters per day given the shape factor shown. To meet that rate, the system would have to pull out one kilowatt of heat continuously. This is 3400 BTU/hr, or about a quarter ton of refrigeration.

Now, suppose the bulb at the bottom has a volume greater than twice the 37 liters. Let's be generous and call it 100 liters. This bulb would have an approximate area of about 1/3 of a square meters, and the resulting heat flux would be about 3000 W/m². For a temperature difference of 20 C, the heat transfer coefficient would be 150 W/m²/C, which would be difficult to generate in this configuration. Furthermore, if the soil is wet mud (best case), it has a specific heat of 2.5 kW-sec/kg/C. This means that in one day, the heat required is enough to raise the temperature of 34500 kg of soil one degree, which is approximately 22 cubic meters of soil. And it will have do this every day. Also, that heat is not uniformly distributed through the soil, so, to maintain the heat extraction rate, you would need a higher heat transfer rate, since the soil temperature will approach the inlet air temperature.

So while the system may produce small amounts of water, it is by no means any more efficient than solar water collectors.

[Read Write Repeat]

Desalinate the Pacific water source, you NIMBY liberals.

[Garth Tater]

You left out convective heat flow and only used conductive heat flow. Whoops. Plenty of subsurface water flowing in many places.

suppose the bulb at the bottom has a volume greater than twice the 37 liters. Let's be generous and call it 100 liters.

Suppose it has 1000 liters. Lets be generous. Do you actually know the surface area used to cool the air in this device? You appear to have used a spherical shape for the conductive interface. Why? If I were to have chosen you to design this device for me I think I would have expected you to MAXIMIZE the surface area of the conductive surface - not MINIMIZE it. Then again, I don't think I would have chosen you to be on the design team. I like real world results, not simplified mathematical analyses.

For a temperature difference of 20 C

No where near that temperature differential is needed. Just enough to lower the air's temperature down to the dew point. Do you know what that temperature differential actually is? How could you? It's a varying number that depends on location and time of day and day of the year, etc. Are you going to make assumptions about those varying numbers and then do the necessary mathematical summations and integrations? Did you notice the word "assumptions" in there? Without the assumptions your analysis is worthless and then with the assumptions your results are worthless without real, out in the dirt testing.

You do a lot of math that ends up being useless because it is not a complete analysis. Without TESTING the device in real-world situations you should not be making blanket statements as to whether or not it actually works. The only point you have that you can hang your hat on is that it is unlikely to meet its advertised 37 liters per day. Big whoop - did you read the fine print. It might be over advertised or it might not but you know what, my car didn't get the 32 mpg it advertised and I didn't expect it to. IT'S ADVERTISING FOR CRYING OUT LOUD. And as I've already told you, my original post and my follow up posts were not about the usefulness or effectiveness of this device it was about the incorrect statement made about it.

This device was designed by actual engineers and I wouldn't be surprised if there was an actual physicist or two involved. People and/or corporations invested money in the design, development and production of this device. Do you think they didn't do their due diligence before investing? This due diligence would have included hands-on inspection, in depth analyses (unlike your superficial analysis) and then testing - both for results and reliability. This would then have been followed up by independent third party reviews by experts in the field. Do you really want to put your half-baked analysis up against what this product went through before production on it started?

Nice analysis you did there - too bad is was just a superficial analysis and by no means worthy of further discussion.

[kosciusko51]

First, my analysis doesn’t directly address conduction/convection in the soil; it addresses what energy is required and heat flux is needed.

Second, my assumptions were based on the representative graphics from the video (”as advertised”). So, yes, if the design changes, that affects the analysis. The bulb in the video is roughly the size I described, and is roughly spherical in shape. As I have been saying previously, their design does not have enough area. If I was to design it, I WOULD use more area.

Third, I used 20 C, since the average soil temperature is about 10 C, and for a majority of the world, the average maximum temperature is about 30 C. That is just to compute the heat transfer rate required. If the temperature difference is lower, one needs higher a heat transfer coefficient.

Furthermore, the energy required is to just covert water vapor to liquid; additional cooling is less than 1% of the total energy. That is pure latent heat of 37 kg/day times 2265 kW-sec/kg. You don’t need to know anything about the relative humidity to get this answer, as it is independent of RH. RH only comes into play to compute the required air flow rate (which is another issue which would have to be addressed once the surface area issue is resolved).

As for your last comment, I’ve had to set straight more than one customer regarding thermal issues as part of peer review. Sometimes doing the most basic energy balance can spot errors.

[Zippo44]

http://www.dailymail.co.uk/news/article-2301226/Fog-catchers-attempt-harvest-moisture-huge-nets-Chilean-desert.html

[Baynative]

I used to live in Monterey, CA.. There is a small incorporated area on the bay called Sand City where there was once a big dredging operation to feed a concrete plant that was built right into the sand dunes.

In the mid 90's there was a continual water restriction put on in the dry months of the summer and some sound minded people came up with a proposal to use the old concrete plant with rusting conveyors and mixing equipment to build a tidal driven desalination plant. The whole idea and process was well thought out and could have provided the whole area with a clean renewal water resource and also a future electric generation potential, too.

As you might expect, liberals shot it down. The droughts and water shortages continue.

[Garth Tater]

First, my analysis doesn’t directly address conduction/convection in the soil; it addresses what energy is required and heat flux is needed.

The convection of heat away from the heat interface is directly related to your calculations and you ignored it.

I used 20 C, since the average soil temperature is about 10 C, and for a majority of the world, the average maximum temperature is about 30 C.

And I explicitly said that there are places on this planet where this device could be used but you said the area of the heat interface was a "show-stopper." Let's stick to what was actually said and not average temperatures.

Another problem - and one that you totally missed - is the difference between day time and night time temperatures. If the night time temperatures are below the average temperature of the affected soil then the device will be spending half of the time COOLING the soil and half of the time WARMING the soil and the net effect overall may be ZERO. Whoops. Didn't include that in your superficial analysis did you?

Why do you persist? This is a real product that went through real design, development and testing. You do not have the information necessary to declare this device unworkable.

That is pure latent heat of 37 kg/day times 2265 kW-sec/kg. You don’t need to know anything about the relative humidity to get this answer

Correct, the energy required to covert water vapor to liquid is not dependent on the humidity level but humidity level does affect the overall amount of air that will have to be pushed through the device to achieve a set amount of condensate and hence the amount of heat energy that will be transferred to the soil by the air (not including the heat absorped by the soil in converting the water vapor to liquid form.) How much of the heat transferred to the soil is released by the latent heat during the phase change and how much by the air flowing past the interface? It can't be calculated by the information we know, nor can it be calculated without knowing the specific parameters of the location this device is installed in. You can assume this energy is in addition the energy absorbed by the phase change of the water vapor but that would be ignoring the cooling effect of the colder night time air flowing through the system.

And finally, you do realize that people have been using earth cooled air to accumulate appreciable quantities of water for thousands of years don't you? And you do realize this device is likely much more efficient than anything people back then could build, right? So with the evidence that earth cooled water condensation systems have been built and used for thousands of years WHY do you persist in saying this device can't work?

[kosciusko51]

You persist in mischaracterizing what I am saying, which is simply this: given the form factor shown in the video, they will not produce 37 kg water/day.

And the form factor they are using highlights the ease in which it can be installed. A design that meets their advertised rate will need to be larger and, most likely, more complex.

[Garth Tater]

And you completely missed and are now ignoring the fact that the heating/cooling cycle is reversed during the night time in many places on the globe. Thanks for playing.

[kosciusko51]

Okay, when the air temperature is lower than the soil temperature, yes, it will extract heat from the soil, but at the same time, it will also not produce any additional condensation. So, now you need even higher heat transfer rates during the heat of the day to meet the 37 kg/day.

Also, when I said what the heat transfer rate should be, this is the requirements based on surface area, temperature differential, and heat rate. How this is met is based on conduction and convection, but the average heat rate is based on the latent heat of condensation and the average water production rate.

Why do you have faith that the form factor shown will produce 37 kg/hr?

[Garth Tater]

Okay, when the air temperature is lower than the soil temperature, yes, it will extract heat from the soil, but at the same time, it will also not produce any additional condensation.

So your "show-stopper" is now not a show-stopper, or am I mischaracterizing what you are saying? And yes, it may not be producing any additional condensate during the night but it certainly could be blowing some nice, warm air through your hut during those cold, frosty nights. And you do realize that the heat saturation of the soil that you have so carefully analyzed is now only happening for part of the day and is possibly being reversed at night and that due to this counter cycle the surrounding soil may never even approach the degree of saturation that you calculated, right? I hope you didn't spend too much time on those calculations.

How this is met is based on conduction and convection

And who was ignoring convection until I brought it up?

How this is met is based on conduction and convection, but the average heat rate is based on the latent heat of condensation and the average water production rate.

No. Those are factors in the calculations, but the humidity level is also a factor due to its relationship to the quantity of air that must be pushed through the system. This air flow, when it is warmer than the soil, also transfers heat to the soil and you can't ignore it in your analysis.

Why do you have faith that the form factor shown will produce 37 kg/hr?

I don't and I've told you twice that I was not expressing an opinion on the effectiveness of this device just that it could be useful in some, even many locations on this planet. My original post and my following posts, except for the ones where I was critiquing and correcting your analysis, was to point out an error another Freeper made early on in this thread.

[kosciusko51]

And I have agreed that this will produce water, just not in the quantities described with the shape factor shown.

[kosciusko51]

Those are factors in the calculations, but the humidity level is also a factor due to its relationship to the quantity of air that must be pushed through the system. This air flow, when it is warmer than the soil, also transfers heat to the soil and you can't ignore it in your analysis.

You do realize that including this effect makes it less likely to work?

[Garth Tater]

You do realize that including this effect makes it less likely to work?

Of course, if you read what I said I said that it adds to the heat being absorbed by the soil. Do you realize that it makes what you said concerning the humidity level not being a factor incorrect?

And do you realize that ignoring convection made your analysis incomplete?

And do you realize that ignoring the counter cyclical effect of cooler night time air made your ENTIRE analysis worthless?

You really need to stop digging.

[BwanaNdege]

Thanks!

It has been a lot of fun - very satisfying.

:-)

[Scythian_Reborn]

If everyone had one of these it would tap the atmosphere of water so heavily it would never rain again. I am warning you all, this represents an extinction level event, I repeat, I don’t know what I’m talking about ...