Re: [compost_tea] Flow rate for air pumps

From: David Anderson <squtch_at_gmail.com>
Date: Thu, 17 Feb 2005 22:14:28 -0800
It seems to me that the size of the pump would depend on the design of
the brewer, and what you are attempting to do with the pump.

The air inside the bubbles are responsible for only a fraction of the
gas exchange in your container.

Their primary job is to move the low O2, high CO2 water to the surface
where there is a lot more surface area and a larger volume of gas to
exchange. The more air and the more water gets moved.

The bubbles breaking at the surface also create turbulance, which
helps with the gas exchange.

And finally, I expect that the bubbles themselves produce the least ,
though still considerable gas exchange.

Just dropping an airstone into a bucket can get some incredible water
currents going. By directing that current, you could greatly increase
the gas exchange area.

That design posted the other day using a water cooler bottle is an
example of engineering airlift pumps to drive a large vortex,  which
drastically increases the surface area, and the turnover of water
contacting that surface. Personally, I suspect that the 100 l/min pump
that was used is far more than should be required, but I have not
tried it yet.

When it comes to larger brewers, I would think that a much more
important criteria in the pumps is the volume produced at the pressure
at the bottom of the tank, instead of looking at tthe no restriction
volume. With a 500 gallon tank design that allows good water movement,
you could probably get away with a pump able to put the same volume of
air in at the bottom, as you would use in a 100 gallon tank. It would
take a stronger pump, to get the air deeper, but the same volume of
air would get the water moving faster from the greater depth.

Of course, this is all theory, with no hard experience to back it up.
So just use it as something to consider when looking at the actual
experiences that others have.

Dave


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Received on Fri Feb 18 2005 - 12:20:36 EST

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