Re:Kevin Conlin's tank design
To: Aquatic-Plants at actwin_com
Subject: Re:Kevin Conlin's tank design
From: Charley Bay <charleyb at hpgrla_gr.hp.com>
Date: Fri, 13 Oct 95 9:00:10 MDT
In-Reply-To: <199510121939.PAA03430 at looney_actwin.com>; from "Aquatic-Plants-Owner at actwin_com" at Oct 12, 95 3:39 pm
Mailer: Elm [revision: 70.85]
>Way back when, Paul Krombholz wrote:
>> Kevin Conlin <kcconlin at cae_ca> described in Digest VI #55:
>>> Aeration chamber
>>> | |
>>> --------------- Nutrient ---------------
>>> | _____________ -> Water Flow -> _____________ |
>>> | | |____________________| | |
>>> | | | chamber water| | |
>>> | ------- level set here| | |
>>> |--- | | ------- Water Line --------------------- | | ----|
>>> | |______ | | |
>>> | | | Powerhead | | |
>>> |----- | | ------------2" Gravel -------------------- | | ----|
>>> |_ _ _ | |_ _ _ _ _ _ _ Fine Mesh _ _ _ _ _ _ _ _ _ _ | |_ _ _|
>>> | 2" Root Growth Area (no gravel) |
>> The pathway of the nutrient water flow above the tank water level will have
>> to be completely air tight. If air can get in, the weight of the water
>> column above the tank water line will force the nutrient solution up
>> through the fine mesh and through the gravel into the tank water.
> Am I missing something? My EE brain figures that because the water flow
> up the riser tube on the left is exactly matched by the flow down the
> tube at the right, there won't be any mixing between the plenum and
> the main tank water (to a first approximation). Water level in the
> aeration chamber (which must remain open for oxygenation) is set by
> the height of the outflow tube.
Oh. I see now. Your EE brain is right. :-) I thought it needed
to be air-tight also, but not so:
In a non-air-sealed system, the water level in the "down"
tube will *always* reach the same level as that in the main
body of the tank.
(x) You don't need an air-tight system if you have a never-broken
"siphon" pulling water up from from the plenum (like a
powerhead in a lift tube with the powerhead below tank level).
This appears to be your design. A pump in the aeration
chamber above water level would require an air-tight seal
for the substrate circulation system (which does not appear
to be your design).
(x) The water in the plenum on the LEFT side is under negative
pressure because of the powerhead, and thus water is pulled
up the tube. Water in the main tank may be drawn down
into the substrate by this localized vacuum, but encounters
resistence moving through the substrate.
(x) The water can flow across the aeration chamber under
relatively low net pressure and mix with air/nutrients,
with the only significant force being the slight differential
(slight drop caused by gravity) induced by a "high" water
level on the left side (caused by the powerhead), and a "low"
water level on the right side (caused by the hydraulic sink:
the right tube, where water "falls" into the tube to the water
level of the tank).
(x) In a non-air-sealed substrate circulation system (your design),
the water in the "down" tube will *always* reach equilibrium
at the main tank level. Thus, net gravitational force should
be zero, and you should (primarily, other then osmotic
gradients) circulate only through the substrate. Likewise,
net pressure will be zero for a sealed system where no air
is exchanged through your substrate circulation.
(x) Of course, if greater evaporation occurs in the main tank,
water will move from the substrate to compensate. Likewise,
if greater evaporation occurs in your aeration chamber,
water will move from the tank into your plenum. You will
never have a water level in your down tube different from
the water level in the tank, and you can add make-up water
to the tank or to the aeration chamber to force temporary
> [snip] the amount of mixing [between the tank and the plenum]
> should be negligible at low flow rates.
Ok, you're right.
--charley Fort Collins, Colorado USA
charleyb at gr_hp.com or charley at agrostis_nrel.colostate.edu