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Re: CO2 diffusion

To: Aquatic-Plants at actwin_com
Subject: Re: CO2 diffusion
From: Paul Sears <psears at nrn1_NRCan.gc.ca>
Date: Thu, 8 Apr 1999 09:27:19 -0400 (EDT)
In-Reply-To: <199904060748.DAA22986 at acme_actwin.com> from "Aquatic Plants Digest" at Apr 6, 99 03:48:02 am

> From: Wright Huntley <huntley1 at home_com>
> Subject: CO2 and agitation
> 
> For the life of me, I can't figure out why agitating the surface could cause
> *any* significant loss of CO2 under those fairly normal circumstances. The CO2
> in the trapped air and the CO2 in solution will still be at equilibrium, and
> there is no place for much CO2 to get away.

	If it is tightly covered, agreed.
> 
> Even in open-top tanks, the heavier CO2 concentrates on the surface and only
> slowly diffuses into the room. *If* you had an active fan blowing air across the
> surface, and *if* you did not have any cover, your evaporative losses and CO2
> depletion could be high. Otherwise, I'm having a problem understanding what the
> problem really is. ;-)

	I think you will find that gaseous diffusion is pretty quick.  You have
a big surface area (in an open tank) and a pretty low CO2 injection rate.  I 
doubt that the CO2 concentration above the water is much above ambient.  I
have done some rough calculations that support this, using actual diffusion
coefficients.
	Any air current at all will sweep it away as well.


-- 
Paul Sears        Ottawa, Canada

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