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Author Topic: Aeration of Ponds  (Read 3723 times)

Offline AlanF

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Aeration of Ponds
« on: 31/12/2014 17:41:02 »
Hello, I wonder if someone can help me settle an argument
In koi ponds it is common to use air pumps and diffusers to pump air into the water for oxygenation purposes. The air leaving the pump is warm/hot after compression, my friend insists this then warms the water when it enters the pond, I think that when it expands there will be little or no difference.
Lets say its a 60litres a minute pump releasing air at 1.2m depth. What would be the effect if the air and pond temperatures were equal?


 

Offline chiralSPO

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Re: Aeration of Ponds
« Reply #1 on: 31/12/2014 19:56:03 »
It isn't just an issue of the heat of compression. One must also consider the waste heat produced by the pump. This will depend on the design and size of the pump, as well as how it is implemented. Also, depending on the humidity of the air being bubbled through the pond, increased rate of evaporation of the water will have a cooling effect, and may even ultimately cause a net cooling...
 

Offline AlanF

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Re: Aeration of Ponds
« Reply #2 on: 01/01/2015 12:33:47 »
It isn't just an issue of the heat of compression. One must also consider the waste heat produced by the pump. This will depend on the design and size of the pump, as well as how it is implemented. Also, depending on the humidity of the air being bubbled through the pond, increased rate of evaporation of the water will have a cooling effect, and may even ultimately cause a net cooling...

Interesting, I had not considered the humidity factor. As for the pump waste heat, lets assume it is lost to the atmosphere. It would not be difficult to utilize it but no one bothers atm.
What might the cooling effect be of someone running the air pump in winter with cold dry air at say, 0C through a pond at 8C?
My main question though is what happens to the warm compressed air when it expands into the water is there a gain or loss to the water temperature as it travels to the surface, everything else being equal?
 

Offline CliffordK

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Re: Aeration of Ponds
« Reply #3 on: 02/01/2015 08:37:56 »
I would assume most of your aeration is done with high volume, low pressure pumps, so the compression is minimal, although there is some compression required to get the air 3 or 4 feet deep. 

If one described an "ideal" system:
  • No friction heat gain from compressor
  • No heat loss to atmosphere from piping/tubing
  • Pump at same elevation as the water surface (1 ATM air pressure)
  • Atmosphere and water temperature are the same
  • No absorption of gasses by the water
  • No evaporation
  • Air bubbles become same temperature as the surrounding water

You can pressurize the air at high or low pressure.  By the time the bubbles reach the surface, they will be at 1 ATM pressure, and thus any heating from compression would be lost.

So, the net heating/cooling in the ideal system would be zero. 

The real system may experience a minimal effect, perhaps some evaporative cooling as  chiralSPO suggested.

You could also add something like an air cooled diesel intercooler to augment the cooling effect.
 

Offline AlanF

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Re: Aeration of Ponds
« Reply #4 on: 02/01/2015 12:57:51 »
Thank you both for the replies.
 If I understand you correctly then even though the air in the pipe leaving the compressor is hot this heat is not transfered to the water by the time the air has expanded into the water. The average pump is rated at 44W so if I assume some loss and 40W is entering the pond this generates quite a large movement in the water due to displacement (which is one of the main reasons for doing it) is that where most/all of the energy is going?
Also could anyone comment on the effect of dry air being pumped through the water- would the evaporation effect cause significant heat loss? The above pump will deliver around 50 lpm  at1.5m deep.
« Last Edit: 03/01/2015 16:13:25 by AlanF »
 

Offline Atomic-S

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Re: Aeration of Ponds
« Reply #5 on: 06/01/2015 04:03:33 »
Don't forget to allow for the conversion of work to heat as the bubbles ascend against the viscosity of the water, churning it.
 

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Re: Aeration of Ponds
« Reply #5 on: 06/01/2015 04:03:33 »

 

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