Published on Nov 1, 2013
I really like the idea of aerating
the fish tank by venturi to save some coin & help make the system
quieter.. A mate shared an idea with me for a unit he had been working
on & was happy with...
I decided to have a crack at his idea along
with a few others to see which I thought would work the best for our set
up...
I was most pleased with the results & ended up going with the
"Bear Unit".. I have had one in the aquaponic fish tank for over 2 weeks
now with no issues & have plans to add another to a moving bed bio
filter that will be added to the system soon...
Was also very pleased with the off the shelf unit purchased from Earthan group.. That one will be going into the moving bed bio filter in the recirculating aquaculture system..
Below are a couple of pages I found helpful when looking into venturis,
http://www.youtube.com/watch?v=Wokswr...
http://en.wikipedia.org/wiki/Venturi_...
http://leisure.prior-it.co.uk/venturi...
Below is an explanation of "Fine bubble aeration" along with some useful links/references,
http://en.wikipedia.org/wiki/Water_ae...
Hope this is of help to some out there...
For more regular updates from the chooks, worms, aquaponic & wicking gardens come visit us at http://www.facebook.com/Bitsouttheback
Have a great one all...
The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe. The Venturi effect is named after Giovanni Battista Venturi (1746–1822), an Italian physicist.
Background
The Venturi effect is a jet effect; as with a funnel the velocity of
the fluid increases as the cross sectional area decreases, with the static pressure correspondingly decreasing.
According to the laws governing fluid dynamics, a fluid's velocity must increase as it passes through a constriction to satisfy the principle of continuity, while its pressure must decrease to satisfy the principle of conservation of mechanical energy.
Thus any gain in kinetic energy a fluid may accrue due to its increased velocity through a constriction is negated by a drop in pressure.
When a fluid such as water flows through a tube that narrows to a
smaller diameter, the partial restriction causes a higher pressure at
the inlet than that at the narrow end.
This pressure difference causes
the fluid to accelerate toward the low pressure narrow section, in which
it thus maintains a higher speed.
The Venturi meter uses the direct
relationship between pressure difference and fluid speeds to determine
the volumetric flow rate.
Relationship between pressure and flow speed
An equation for the drop in pressure due to the Venturi effect may be derived from a combination of Bernoulli's principle and the continuity equation.
Referring to the diagram to the right, using Bernoulli's equation in
the special case of incompressible flows (such as the flow of water or
other liquid, or low speed flow of gas), the theoretical pressure drop
at the constriction is given by:
is the density of the fluid, 
is the (slower) fluid velocity where the pipe is wider, 
is the (faster) fluid velocity where the pipe is narrower (as seen in
the figure). This assumes the flowing fluid (or other substance) is not
significantly compressible - even though pressure varies, the density is
assumed to remain approximately constant.Choked flow
The limiting case of the Venturi effect is when a fluid reaches the
state of choked flow, where the fluid velocity approaches the local
speed of sound.
In choked flow the mass flow rate will not increase
with a further decrease in the downstream pressure environment.
However,
mass flow rate for a compressible fluid can increase with increased
upstream pressure, which will increase the density of the fluid through
the constriction (though the velocity will remain constant).
This is
the principle of operation of a de Laval nozzle. Increasing source temperature will also increase the local sonic velocity, thus allowing for increased mass flow rate.
Source: Wikipedia.org
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