Tuesday, February 18, 2014

DIY Venturi~ " A Few Easy Builds for Aquaponics, Aquaculture, or Hydroponics"


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.



The pressure in the first measuring tube (1) is higher than at the second (2), and the fluid speed at "1" is lower than at "2", because the cross-sectional area at "1" is greater than at "2".

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.



A flow of air through a venturi meter, showing the columns connected in a U-shape (a manometer) and partially filled with water. The meter is "read" as a differential pressure head in cm or inches of water.

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:
p_1 - p_2 = \frac{\rho}{2}\left(v_2^2 - v_1^2\right)
where \scriptstyle \rho\, is the density of the fluid, \scriptstyle v_1 is the (slower) fluid velocity where the pipe is wider, \scriptstyle v_2 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.



Flow in a Venturi tube

 

 

Source: Wikipedia.org


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