I have been doing a lot of research on the Internet lately about desalination processes and desalination plants and this led me to studying mountain weather and the orographic effect or orographic lifting.

The thought then occurred to me about whether a lot of fresh water could be produced by creating an artificially-produced orographic effect by pumping warm, humid coastal air through a pipeline that would lead to the top of a coastal mountain.

Orographic Effect:

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I then made a conceptual drawing in MS Paint on how this could be done:

enter image description here

The temperature of the metal pipe will decrease as it ascends up the coastal mountain and this colder metal should cause the water vapor within the pumped air to condense on the inner wall of the pipeline forming water droplets. These water droplets will then be pulled down by gravity and should fall into a pipe leading to a water storage tank.

In the case that one air pumping plant cannot produce enough air pressure to push the air all the way up a mountain, then perhaps another air pumping plant would need to be stationed at the top of the mountain to assist with transporting the air upwards through the pipeline.

These air pumping plants would need to have a large volume industrial centrifugal blower fan like the ones built by Elektror Airsystems pictured here:

enter image description here

Reference: https://www.elektror.com/en/products/industrial-blowers/large-volume-fans/

I am neither a climatologist nor a physicist so I really don't how much fresh water could be produced this way. I am looking for someone in Physics.SE to give me just a ballpark figure of how much water would be produced by this process on any given day.

Say that the pipeline is 8 feet in diameter, the top of the mountain is 8,000 ft high, the air temperature at the top of the mountain is 45 degrees, the coastal air temperature is 84 degrees, and the coastal air humidity is 70%.

Would pumping warm humid air through a pipeline up to the top of a mountain produce a lot of fresh water?

  • 1
    $\begingroup$ Skip the pipe and the pump: use "fog harvesting youtu.be/h8vlzZ25vtg $\endgroup$
    – DJohnM
    Jan 13, 2023 at 21:53
  • $\begingroup$ @DJohnM, I actually saw that video a few days ago and I really like that idea. The only downside I see to that process is that it is rather slow and the weather is unpredictable on a day-to-day basis. $\endgroup$
    – user57467
    Jan 13, 2023 at 21:56
  • 1
    $\begingroup$ how about unidirectional valves at the pumping station sites, instead of actives pumps? rely on passive natural process rather than powered. yield would be lower, but could run in parallel along appropriate coastline & operating costs would be a fraction. $\endgroup$
    – antimony
    Jan 14, 2023 at 3:22
  • $\begingroup$ One has to count with dry (1 K/100 m) + wet (0.6-0.7 K / 100 m) adiabatical cooling that may lead to air both warmer and cooler than ambient air at the top station. // Another factor is kinetics of condensation, as air may get supersaturated and water may not condense fast enough to be caught. Capacity of fog separation is another matter. // By principle, I refuse to use imperial units, it has already caused too many costly misunderstandings. $\endgroup$
    – Poutnik
    Jan 15, 2023 at 12:09

1 Answer 1


That's going to depend on the amount of air that you push through the pipe. And that's going to depend on how much power you put in the fans. Unfortunately, such a long pipe is going to have significant frictional loss.

Also, just because the ambient temperature at the top is 45F doesn't mean that you can chill the interior that much. The faster the air moves, the less time it has to equilibrate. Fins would help it equilibrate, but would increase the power required.

Since you're cooling the air, you basically have the same process as any other air conditioner or dehumidifier. So your device isn't going do any better than those devices with similar air flow. If you can determine your flow rate, you can use a condensate calculator to estimate the max you could collect.

I used one and with 84F dry bulb, 76F web bulb (70%RH), 45F target and 1000 CFM airflow (that's about the size of a smaller residential whole-house attic fan). Assuming you could get that flow through the pipe, and it actually chills the interior to the target temperature, max possible is a bit less than 5 gallons an hour.

  • $\begingroup$ perhaps slow moving air inside the pipeline would be better than a fast airflow rate because this should mean that the rising air mass has more time to equilibrate. $\endgroup$
    – user57467
    Jan 14, 2023 at 12:12
  • $\begingroup$ That would take less power. But if you're interested in quantities, then it will produce less water. $\endgroup$
    – BowlOfRed
    Jan 14, 2023 at 20:53

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